gecko/mozglue/build/Nuwa.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

#include <map>
#include <memory>

#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <setjmp.h>
#include <signal.h>
#include <poll.h>
#include <pthread.h>
#include <alloca.h>
#include <sys/epoll.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <vector>

#include "mozilla/LinkedList.h"
#include "Nuwa.h"

using namespace mozilla;

/**
 * Provides the wrappers to a selected set of pthread and system-level functions
 * as the basis for implementing Zygote-like preforking mechanism.
 */

/**
 * Real functions for the wrappers.
 */
extern "C" {
int __real_pthread_create(pthread_t *thread,
                          const pthread_attr_t *attr,
                          void *(*start_routine) (void *),
                          void *arg);
int __real_pthread_key_create(pthread_key_t *key, void (*destructor)(void*));
int __real_pthread_key_delete(pthread_key_t key);
pthread_t __real_pthread_self();
int __real_pthread_join(pthread_t thread, void **retval);
int __real_epoll_wait(int epfd,
                      struct epoll_event *events,
                      int maxevents,
                      int timeout);
int __real_pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mtx);
int __real_pthread_cond_timedwait(pthread_cond_t *cond,
                                  pthread_mutex_t *mtx,
                                  const struct timespec *abstime);
int __real___pthread_cond_timedwait(pthread_cond_t *cond,
                                    pthread_mutex_t *mtx,
                                    const struct timespec *abstime,
                                    clockid_t clock);
int __real_pthread_mutex_lock(pthread_mutex_t *mtx);
int __real_poll(struct pollfd *fds, nfds_t nfds, int timeout);
int __real_epoll_create(int size);
int __real_socketpair(int domain, int type, int protocol, int sv[2]);
int __real_pipe2(int __pipedes[2], int flags);
int __real_pipe(int __pipedes[2]);
int __real_epoll_ctl(int aEpollFd, int aOp, int aFd, struct epoll_event *aEvent);
int __real_close(int aFd);

}

#define REAL(s) __real_##s

/**
 * A Nuwa process is started by preparing.  After preparing, it waits
 * for all threads becoming frozen. Then, it is ready while all
 * threads are frozen.
 */
static bool sIsNuwaProcess = false; // This process is a Nuwa process.
static bool sIsFreezing = false; // Waiting for all threads getting frozen.
static bool sNuwaReady = false;  // Nuwa process is ready.
static bool sNuwaPendingSpawn = false; // Are there any pending spawn requests?
static bool sNuwaForking = false;

// Fds of transports of top level protocols.
static NuwaProtoFdInfo sProtoFdInfos[NUWA_TOPLEVEL_MAX];
static int sProtoFdInfosSize = 0;

template <typename T>
struct LibcAllocator: public std::allocator<T>
{
  LibcAllocator()
  {
    void* libcHandle = dlopen("libc.so", RTLD_LAZY);
    mMallocImpl = reinterpret_cast<void*(*)(size_t)>(dlsym(libcHandle, "malloc"));
    mFreeImpl = reinterpret_cast<void(*)(void*)>(dlsym(libcHandle, "free"));

    if (!(mMallocImpl && mFreeImpl)) {
      // libc should be available, or we'll deadlock in using TLSInfoList.
      abort();
    }
  }

  inline typename std::allocator<T>::pointer
  allocate(typename std::allocator<T>::size_type n,
           const void * = 0)
  {
    return reinterpret_cast<T *>(mMallocImpl(n));
  }

  inline void
  deallocate(typename std::allocator<T>::pointer p,
             typename std::allocator<T>::size_type n)
  {
    mFreeImpl(p);
  }

  template<typename U>
  struct rebind
  {
    typedef LibcAllocator<U> other;
  };
private:
  void* (*mMallocImpl)(size_t);
  void (*mFreeImpl)(void*);
};

/**
 * TLSInfoList should use malloc() and free() in libc to avoid the deadlock that
 * jemalloc calls into __wrap_pthread_mutex_lock() and then deadlocks while
 * the same thread already acquired sThreadCountLock.
 */
typedef std::vector<std::pair<pthread_key_t, void *>,
                    LibcAllocator<std::pair<pthread_key_t, void *> > >
TLSInfoList;

/**
 * The stack size is chosen carefully so the frozen threads doesn't consume too
 * much memory in the Nuwa process. The threads shouldn't run deep recursive
 * methods or do large allocations on the stack to avoid stack overflow.
 */
#ifndef NUWA_STACK_SIZE
#define NUWA_STACK_SIZE (1024 * 32)
#endif

struct thread_info : public mozilla::LinkedListElement<thread_info> {
  pthread_t origThreadID;
  pthread_t recreatedThreadID;
  pthread_attr_t threadAttr;
  jmp_buf jmpEnv;
  jmp_buf retEnv;

  int flags;

  void *(*startupFunc)(void *arg);
  void *startupArg;

  // The thread specific function to recreate the new thread. It's executed
  // after the thread is recreated.
  void (*recrFunc)(void *arg);
  void *recrArg;

  TLSInfoList tlsInfo;

  pthread_mutex_t *reacquireMutex;
  void *stk;
};

typedef struct thread_info thread_info_t;

static thread_info_t *sCurrentRecreatingThread = NULL;

/**
 * This function runs the custom recreation function registered when calling
 * NuwaMarkCurrentThread() after thread stack is restored.
 */
static void
RunCustomRecreation() {
  thread_info_t *tinfo = sCurrentRecreatingThread;
  if (tinfo->recrFunc != NULL) {
    tinfo->recrFunc(tinfo->recrArg);
  }
}

/**
 * Every thread should be marked as either TINFO_FLAG_NUWA_SUPPORT or
 * TINFO_FLAG_NUWA_SKIP, or it means a potential error.  We force
 * Gecko code to mark every single thread to make sure there are no accidents
 * when recreating threads with Nuwa.
 *
 * Threads marked as TINFO_FLAG_NUWA_SUPPORT can be checkpointed explicitly, by
 * calling NuwaCheckpointCurrentThread(), or implicitly when they call into wrapped
 * functions like pthread_mutex_lock(), epoll_wait(), etc.
 * TINFO_FLAG_NUWA_EXPLICIT_CHECKPOINT denotes the explicitly checkpointed thread.
 */
#define TINFO_FLAG_NUWA_SUPPORT 0x1
#define TINFO_FLAG_NUWA_SKIP 0x2
#define TINFO_FLAG_NUWA_EXPLICIT_CHECKPOINT 0x4

typedef struct nuwa_construct {
  void (*construct)(void *);
  void *arg;
} nuwa_construct_t;

static std::vector<nuwa_construct_t> sConstructors;
static std::vector<nuwa_construct_t> sFinalConstructors;

typedef std::map<pthread_key_t, void (*)(void *)> TLSKeySet;
static TLSKeySet sTLSKeys;

/**
 * This mutex is used to block the running threads and freeze their contexts.
 * PrepareNuwaProcess() is the first one to acquire the lock. Further attempts
 * to acquire this mutex (in the freeze point macros) will block and freeze the
 * calling thread.
 */
static pthread_mutex_t sThreadFreezeLock = PTHREAD_MUTEX_INITIALIZER;

static LinkedList<thread_info_t> sAllThreads;
static int sThreadCount = 0;
static int sThreadFreezeCount = 0;
/**
 * This mutex protects the access to thread info:
 * sAllThreads, sThreadCount, sThreadFreezeCount, sRecreateVIPCount.
 */
static pthread_mutex_t sThreadCountLock = PTHREAD_MUTEX_INITIALIZER;
/**
 * This condition variable lets MakeNuwaProcess() wait until all recreated
 * threads are frozen.
 */
static pthread_cond_t sThreadChangeCond = PTHREAD_COND_INITIALIZER;

/**
 * This mutex and condition variable is used to serialize the fork requests
 * from the parent process.
 */
static pthread_mutex_t sForkLock = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t sForkWaitCond = PTHREAD_COND_INITIALIZER;

/**
 * sForkWaitCondChanged will be reset to false on the IPC thread before
 * and will be changed to true on the main thread to indicate that the condition
 * that the IPC thread is waiting for has already changed.
 */
static bool sForkWaitCondChanged = false;

/**
 * This mutex protects the access to sTLSKeys, which keeps track of existing
 * TLS Keys.
 */
static pthread_mutex_t sTLSKeyLock = PTHREAD_MUTEX_INITIALIZER;
static int sThreadSkipCount = 0;

static thread_info_t *
GetThreadInfoInner(pthread_t threadID) {
  for (thread_info_t *tinfo = sAllThreads.getFirst();
       tinfo;
       tinfo = tinfo->getNext()) {
    if (pthread_equal(tinfo->origThreadID, threadID)) {
      return tinfo;
    }
  }

  return NULL;
}

/**
 * Get thread info using the specified thread ID.
 *
 * @return thread_info_t which has threadID == specified threadID
 */
static thread_info_t *
GetThreadInfo(pthread_t threadID) {
  if (sIsNuwaProcess) {
    REAL(pthread_mutex_lock)(&sThreadCountLock);
  }
  thread_info_t *tinfo = GetThreadInfoInner(threadID);
  if (sIsNuwaProcess) {
    pthread_mutex_unlock(&sThreadCountLock);
  }
  return tinfo;
}

#if !defined(HAVE_THREAD_TLS_KEYWORD)
/**
 * Get thread info of the current thread.
 *
 * @return thread_info_t for the current thread.
 */
static thread_info_t *
GetCurThreadInfo() {
  pthread_t threadID = REAL(pthread_self)();
  pthread_t thread_info_t::*threadIDptr =
      (sIsNuwaProcess ?
         &thread_info_t::origThreadID :
         &thread_info_t::recreatedThreadID);

  REAL(pthread_mutex_lock)(&sThreadCountLock);
  thread_info_t *tinfo;
  for (tinfo = sAllThreads.getFirst();
       tinfo;
       tinfo = tinfo->getNext()) {
    if (pthread_equal(tinfo->*threadIDptr, threadID)) {
      break;
    }
  }
  pthread_mutex_unlock(&sThreadCountLock);
  return tinfo;
}
#define CUR_THREAD_INFO GetCurThreadInfo()
#define SET_THREAD_INFO(x) /* Nothing to do. */
#else
// Is not NULL only for threads created by pthread_create() in an Nuwa process.
// It is always NULL for the main thread.
static __thread thread_info_t *sCurThreadInfo = NULL;
#define CUR_THREAD_INFO sCurThreadInfo
#define SET_THREAD_INFO(x) do { sCurThreadInfo = (x); } while(0)
#endif  // HAVE_THREAD_TLS_KEYWORD

/*
 * Track all epoll fds and handling events.
 */
class EpollManager {
public:
  class EpollInfo {
  public:
    typedef struct epoll_event Events;
    typedef std::map<int, Events> EpollEventsMap;
    typedef EpollEventsMap::iterator iterator;
    typedef EpollEventsMap::const_iterator const_iterator;

    EpollInfo(): mBackSize(0) {}
    EpollInfo(int aBackSize): mBackSize(aBackSize) {}
    EpollInfo(const EpollInfo &aOther): mEvents(aOther.mEvents)
                                      , mBackSize(aOther.mBackSize) {
    }
    ~EpollInfo() {
      mEvents.clear();
    }

    void AddEvents(int aFd, Events &aEvents) {
      std::pair<iterator, bool> pair =
        mEvents.insert(std::make_pair(aFd, aEvents));
      if (!pair.second) {
        abort();
      }
    }

    void RemoveEvents(int aFd) {
      if (!mEvents.erase(aFd)) {
        abort();
      }
    }

    void ModifyEvents(int aFd, Events &aEvents) {
      iterator it = mEvents.find(aFd);
      if (it == mEvents.end()) {
        abort();
      }
      it->second = aEvents;
    }

    const Events &FindEvents(int aFd) const {
      const_iterator it = mEvents.find(aFd);
      if (it == mEvents.end()) {
        abort();
      }
      return it->second;
    }

    int Size() const { return mEvents.size(); }

    // Iterator with values of <fd, Events> pairs.
    const_iterator begin() const { return mEvents.begin(); }
    const_iterator end() const { return mEvents.end(); }

    int BackSize() const { return mBackSize; }

  private:
    EpollEventsMap mEvents;
    int mBackSize;

    friend class EpollManager;
  };

  typedef std::map<int, EpollInfo> EpollInfoMap;
  typedef EpollInfoMap::iterator iterator;
  typedef EpollInfoMap::const_iterator const_iterator;

public:
  void AddEpollInfo(int aEpollFd, int aBackSize) {
    EpollInfo *oldinfo = FindEpollInfo(aEpollFd);
    if (oldinfo != NULL) {
      abort();
    }
    mEpollFdsInfo[aEpollFd] = EpollInfo(aBackSize);
  }

  EpollInfo *FindEpollInfo(int aEpollFd) {
    iterator it = mEpollFdsInfo.find(aEpollFd);
    if (it == mEpollFdsInfo.end()) {
      return NULL;
    }
    return &it->second;
  }

  void RemoveEpollInfo(int aEpollFd) {
    if (!mEpollFdsInfo.erase(aEpollFd)) {
      abort();
    }
  }

  int Size() const { return mEpollFdsInfo.size(); }

  // Iterator of <epollfd, EpollInfo> pairs.
  const_iterator begin() const { return mEpollFdsInfo.begin(); }
  const_iterator end() const { return mEpollFdsInfo.end(); }

  static EpollManager *Singleton() {
    if (!sInstance) {
      sInstance = new EpollManager();
    }
    return sInstance;
  }

  static void Shutdown() {
    if (!sInstance) {
      abort();
    }

    delete sInstance;
    sInstance = NULL;
  }

private:
  static EpollManager *sInstance;
  ~EpollManager() {
    mEpollFdsInfo.clear();
  }

  EpollInfoMap mEpollFdsInfo;

  EpollManager() {}
};

EpollManager* EpollManager::sInstance;

static thread_info_t *
thread_info_new(void) {
  /* link tinfo to sAllThreads */
  thread_info_t *tinfo = new thread_info_t();
  tinfo->flags = 0;
  tinfo->recrFunc = NULL;
  tinfo->recrArg = NULL;
  tinfo->recreatedThreadID = 0;
  tinfo->reacquireMutex = NULL;
  tinfo->stk = malloc(NUWA_STACK_SIZE);
  pthread_attr_init(&tinfo->threadAttr);

  REAL(pthread_mutex_lock)(&sThreadCountLock);
  // Insert to the tail.
  sAllThreads.insertBack(tinfo);

  sThreadCount++;
  pthread_cond_signal(&sThreadChangeCond);
  pthread_mutex_unlock(&sThreadCountLock);

  return tinfo;
}

static void
thread_info_cleanup(void *arg) {
  if (sNuwaForking) {
    // We shouldn't have any thread exiting when we are forking a new process.
    abort();
  }

  thread_info_t *tinfo = (thread_info_t *)arg;
  pthread_attr_destroy(&tinfo->threadAttr);

  REAL(pthread_mutex_lock)(&sThreadCountLock);
  /* unlink tinfo from sAllThreads */
  tinfo->remove();

  sThreadCount--;
  pthread_cond_signal(&sThreadChangeCond);
  pthread_mutex_unlock(&sThreadCountLock);

  free(tinfo->stk);
  delete tinfo;
}

static void *
_thread_create_startup(void *arg) {
  thread_info_t *tinfo = (thread_info_t *)arg;
  void *r;

  // Save thread info; especially, stackaddr & stacksize.
  // Reuse the stack in the new thread.
  pthread_getattr_np(REAL(pthread_self)(), &tinfo->threadAttr);

  SET_THREAD_INFO(tinfo);
  tinfo->origThreadID = REAL(pthread_self)();

  pthread_cleanup_push(thread_info_cleanup, tinfo);

  r = tinfo->startupFunc(tinfo->startupArg);

  if (!sIsNuwaProcess) {
    return r;
  }

  pthread_cleanup_pop(1);

  return r;
}

// reserve STACK_RESERVED_SZ * 4 bytes for thread_recreate_startup().
#define STACK_RESERVED_SZ 64
#define STACK_SENTINEL(v) ((v)[0])
#define STACK_SENTINEL_VALUE(v) ((uint32_t)(v) ^ 0xdeadbeef)

static void *
thread_create_startup(void *arg) {
  /*
   * Dark Art!! Never try to do the same unless you are ABSOLUTELY sure of
   * what you are doing!
   *
   * This function is here for reserving stack space before calling
   * _thread_create_startup().  see also thread_create_startup();
   */
  void *r;
  volatile uint32_t reserved[STACK_RESERVED_SZ];

  // Reserve stack space.
  STACK_SENTINEL(reserved) = STACK_SENTINEL_VALUE(reserved);

  r = _thread_create_startup(arg);

  // Check if the reservation is enough.
  if (STACK_SENTINEL(reserved) != STACK_SENTINEL_VALUE(reserved)) {
    abort();                    // Did not reserve enough stack space.
  }

  thread_info_t *tinfo = CUR_THREAD_INFO;
  if (!sIsNuwaProcess) {
    longjmp(tinfo->retEnv, 1);

    // Never go here!
    abort();
  }

  return r;
}

extern "C" MFBT_API int
__wrap_pthread_create(pthread_t *thread,
                      const pthread_attr_t *attr,
                      void *(*start_routine) (void *),
                      void *arg) {
  if (!sIsNuwaProcess) {
    return REAL(pthread_create)(thread, attr, start_routine, arg);
  }

  thread_info_t *tinfo = thread_info_new();
  tinfo->startupFunc = start_routine;
  tinfo->startupArg = arg;
  pthread_attr_setstack(&tinfo->threadAttr, tinfo->stk, NUWA_STACK_SIZE);

  int rv = REAL(pthread_create)(thread,
                                &tinfo->threadAttr,
                                thread_create_startup,
                                tinfo);
  if (rv) {
    thread_info_cleanup(tinfo);
  } else {
    tinfo->origThreadID = *thread;
  }

  return rv;
}

// TLS related

/**
 * Iterates over the existing TLS keys and store the TLS data for the current
 * thread in tinfo.
 */
static void
SaveTLSInfo(thread_info_t *tinfo) {
  REAL(pthread_mutex_lock)(&sTLSKeyLock);
  tinfo->tlsInfo.clear();
  for (TLSKeySet::const_iterator it = sTLSKeys.begin();
       it != sTLSKeys.end();
       it++) {
    void *value = pthread_getspecific(it->first);
    if (value == NULL) {
      continue;
    }

    pthread_key_t key = it->first;
    tinfo->tlsInfo.push_back(TLSInfoList::value_type(key, value));
  }
  pthread_mutex_unlock(&sTLSKeyLock);
}

/**
 * Restores the TLS data for the current thread from tinfo.
 */
static void
RestoreTLSInfo(thread_info_t *tinfo) {
  int rv;

  for (TLSInfoList::const_iterator it = tinfo->tlsInfo.begin();
       it != tinfo->tlsInfo.end();
       it++) {
    pthread_key_t key = it->first;
    const void *value = it->second;
    if (pthread_setspecific(key, value)) {
      abort();
    }
  }

  SET_THREAD_INFO(tinfo);
  tinfo->recreatedThreadID = REAL(pthread_self)();
}

extern "C" MFBT_API int
__wrap_pthread_key_create(pthread_key_t *key, void (*destructor)(void*)) {
  int rv = REAL(pthread_key_create)(key, destructor);
  if (rv != 0) {
    return rv;
  }
  REAL(pthread_mutex_lock)(&sTLSKeyLock);
  sTLSKeys.insert(TLSKeySet::value_type(*key, destructor));
  pthread_mutex_unlock(&sTLSKeyLock);
  return 0;
}

extern "C" MFBT_API int
__wrap_pthread_key_delete(pthread_key_t key) {
  if (!sIsNuwaProcess) {
    return REAL(pthread_key_delete)(key);
  }
  int rv = REAL(pthread_key_delete)(key);
  if (rv != 0) {
    return rv;
  }
  REAL(pthread_mutex_lock)(&sTLSKeyLock);
  sTLSKeys.erase(key);
  pthread_mutex_unlock(&sTLSKeyLock);
  return 0;
}

extern "C" MFBT_API pthread_t
__wrap_pthread_self() {
  thread_info_t *tinfo = CUR_THREAD_INFO;
  if (tinfo) {
    // For recreated thread, masquerade as the original thread in the Nuwa
    // process.
    return tinfo->origThreadID;
  }
  return REAL(pthread_self)();
}

extern "C" MFBT_API int
__wrap_pthread_join(pthread_t thread, void **retval) {
  thread_info_t *tinfo = GetThreadInfo(thread);
  if (tinfo == NULL) {
    return REAL(pthread_join)(thread, retval);
  }
  // pthread_join() need to use the real thread ID in the spawned process.
  return REAL(pthread_join)(tinfo->recreatedThreadID, retval);
}

/**
 * The following are used to synchronize between the main thread and the
 * thread being recreated. The main thread will wait until the thread is woken
 * up from the freeze points or the blocking intercepted functions and then
 * proceed to recreate the next frozen thread.
 *
 * In thread recreation, the main thread recreates the frozen threads one by
 * one. The recreated threads will be "gated" until the main thread "opens the
 * gate" to let them run freely as if they were created from scratch. The VIP
 * threads gets the chance to run first after their thread stacks are recreated
 * (using longjmp()) so they can adjust their contexts to a valid, consistent
 * state. The threads frozen waiting for pthread condition variables are VIP
 * threads. After woken up they need to run first to make the associated mutex
 * in a valid state to maintain the semantics of the intercepted function calls
 * (like pthread_cond_wait()).
 */

// Used to synchronize the main thread and the thread being recreated so that
// only one thread is allowed to be recreated at a time.
static pthread_mutex_t sRecreateWaitLock = PTHREAD_MUTEX_INITIALIZER;
// Used to block recreated threads until the main thread "opens the gate".
static pthread_mutex_t sRecreateGateLock = PTHREAD_MUTEX_INITIALIZER;
// Used to block the main thread from "opening the gate" until all VIP threads
// have been recreated.
static pthread_mutex_t sRecreateVIPGateLock = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t sRecreateVIPCond = PTHREAD_COND_INITIALIZER;
static int sRecreateVIPCount = 0;
static int sRecreateGatePassed = 0;

/**
 * Thread recreation macros.
 *
 * The following macros are used in the forked process to synchronize and
 * control the progress of thread recreation.
 *
 * 1. RECREATE_START() is first called in the beginning of thread
 *    recreation to set sRecreateWaitLock and sRecreateGateLock in locked
 *    state.
 * 2. For each frozen thread:
 *    2.1. RECREATE_BEFORE() to set the thread being recreated.
 *    2.2. thread_recreate() to recreate the frozen thread.
 *    2.3. Main thread calls RECREATE_WAIT() to wait on sRecreateWaitLock until
 *         the thread is recreated from the freeze point and calls
 *         RECREATE_CONTINUE() to release sRecreateWaitLock.
 *    2.3. Non-VIP threads are blocked on RECREATE_GATE(). VIP threads calls
 *         RECREATE_PASS_VIP() to mark that a VIP thread is successfully
 *         recreated and then is blocked by calling RECREATE_GATE_VIP().
 * 3. RECREATE_WAIT_ALL_VIP() to wait until all VIP threads passed, that is,
 *    VIP threads already has their contexts (mainly pthread mutex) in a valid
 *    state.
 * 4. RECREATE_OPEN_GATE() to unblock threads blocked by sRecreateGateLock.
 * 5. RECREATE_FINISH() to complete thread recreation.
 */
#define RECREATE_START()                          \
  do {                                            \
    REAL(pthread_mutex_lock)(&sRecreateWaitLock); \
    REAL(pthread_mutex_lock)(&sRecreateGateLock); \
  } while(0)
#define RECREATE_BEFORE(info) do { sCurrentRecreatingThread = info; } while(0)
#define RECREATE_WAIT() REAL(pthread_mutex_lock)(&sRecreateWaitLock)
#define RECREATE_CONTINUE() do {                \
    RunCustomRecreation();                      \
    pthread_mutex_unlock(&sRecreateWaitLock);   \
  } while(0)
#define RECREATE_FINISH() pthread_mutex_unlock(&sRecreateWaitLock)
#define RECREATE_GATE()                           \
  do {                                            \
    REAL(pthread_mutex_lock)(&sRecreateGateLock); \
    sRecreateGatePassed++;                        \
    pthread_mutex_unlock(&sRecreateGateLock);     \
  } while(0)
#define RECREATE_OPEN_GATE() pthread_mutex_unlock(&sRecreateGateLock)
#define RECREATE_GATE_VIP()                       \
  do {                                            \
    REAL(pthread_mutex_lock)(&sRecreateGateLock); \
    pthread_mutex_unlock(&sRecreateGateLock);     \
  } while(0)
#define RECREATE_PASS_VIP()                          \
  do {                                               \
    REAL(pthread_mutex_lock)(&sRecreateVIPGateLock); \
    sRecreateGatePassed++;                           \
    pthread_cond_signal(&sRecreateVIPCond);          \
    pthread_mutex_unlock(&sRecreateVIPGateLock);     \
  } while(0)
#define RECREATE_WAIT_ALL_VIP()                        \
  do {                                                 \
    REAL(pthread_mutex_lock)(&sRecreateVIPGateLock);   \
    while(sRecreateGatePassed < sRecreateVIPCount) {   \
      REAL(pthread_cond_wait)(&sRecreateVIPCond,       \
                        &sRecreateVIPGateLock);        \
    }                                                  \
    pthread_mutex_unlock(&sRecreateVIPGateLock);       \
  } while(0)

/**
 * Thread freeze points. Note that the freeze points are implemented as macros
 * so as not to garble the content of the stack after setjmp().
 *
 * In the nuwa process, when a thread supporting nuwa calls a wrapper
 * function, freeze point 1 setjmp()s to save the state. We only allow the
 * thread to be frozen in the wrapper functions. If thread freezing is not
 * enabled yet, the wrapper functions act like their wrapped counterparts,
 * except for the extra actions in the freeze points. If thread freezing is
 * enabled, the thread will be frozen by calling one of the wrapper functions.
 * The threads can be frozen in any of the following points:
 *
 * 1) Freeze point 1: this is the point where we setjmp() in the nuwa process
 *    and longjmp() in the spawned process. If freezing is enabled, then the
 *    current thread blocks by acquiring an already locked mutex,
 *    sThreadFreezeLock.
 * 2) The wrapped function: the function that might block waiting for some
 *    resource or condition.
 * 3) Freeze point 2: blocks the current thread by acquiring sThreadFreezeLock.
 *    If freezing is not enabled then revert the counter change in freeze
 *    point 1.
 */
#define THREAD_FREEZE_POINT1()                                 \
  bool freezeCountChg = false;                                 \
  bool recreated = false;                                      \
  volatile bool freezePoint2 = false;                          \
  thread_info_t *tinfo;                                        \
  if (sIsNuwaProcess &&                                        \
      (tinfo = CUR_THREAD_INFO) &&                             \
      (tinfo->flags & TINFO_FLAG_NUWA_SUPPORT) &&              \
      !(tinfo->flags & TINFO_FLAG_NUWA_EXPLICIT_CHECKPOINT)) { \
    if (!setjmp(tinfo->jmpEnv)) {                              \
      REAL(pthread_mutex_lock)(&sThreadCountLock);             \
      SaveTLSInfo(tinfo);                                      \
      sThreadFreezeCount++;                                    \
      freezeCountChg = true;                                   \
      pthread_cond_signal(&sThreadChangeCond);                 \
      pthread_mutex_unlock(&sThreadCountLock);                 \
                                                               \
      if (sIsFreezing) {                                       \
        REAL(pthread_mutex_lock)(&sThreadFreezeLock);          \
        /* Never return from the pthread_mutex_lock() call. */ \
        abort();                                               \
      }                                                        \
    } else {                                                   \
      RECREATE_CONTINUE();                                     \
      RECREATE_GATE();                                         \
      freezeCountChg = false;                                  \
      recreated = true;                                        \
    }                                                          \
  }

#define THREAD_FREEZE_POINT1_VIP()                             \
  bool freezeCountChg = false;                                 \
  bool recreated = false;                                      \
  volatile bool freezePoint1 = false;                          \
  volatile bool freezePoint2 = false;                          \
  thread_info_t *tinfo;                                        \
  if (sIsNuwaProcess &&                                        \
      (tinfo = CUR_THREAD_INFO) &&                             \
      (tinfo->flags & TINFO_FLAG_NUWA_SUPPORT) &&              \
      !(tinfo->flags & TINFO_FLAG_NUWA_EXPLICIT_CHECKPOINT)) { \
    if (!setjmp(tinfo->jmpEnv)) {                              \
      REAL(pthread_mutex_lock)(&sThreadCountLock);             \
      SaveTLSInfo(tinfo);                                      \
      sThreadFreezeCount++;                                    \
      sRecreateVIPCount++;                                     \
      freezeCountChg = true;                                   \
      pthread_cond_signal(&sThreadChangeCond);                 \
      pthread_mutex_unlock(&sThreadCountLock);                 \
                                                               \
      if (sIsFreezing) {                                       \
        freezePoint1 = true;                                   \
        REAL(pthread_mutex_lock)(&sThreadFreezeLock);          \
        /* Never return from the pthread_mutex_lock() call. */ \
        abort();                                               \
      }                                                        \
    } else {                                                   \
      freezeCountChg = false;                                  \
      recreated = true;                                        \
    }                                                          \
  }

#define THREAD_FREEZE_POINT2()                               \
  if (freezeCountChg) {                                      \
    REAL(pthread_mutex_lock)(&sThreadCountLock);             \
    if (sNuwaReady && sIsNuwaProcess) {                      \
      pthread_mutex_unlock(&sThreadCountLock);               \
      freezePoint2 = true;                                   \
      REAL(pthread_mutex_lock)(&sThreadFreezeLock);          \
      /* Never return from the pthread_mutex_lock() call. */ \
      abort();                                               \
    }                                                        \
    sThreadFreezeCount--;                                    \
    pthread_cond_signal(&sThreadChangeCond);                 \
    pthread_mutex_unlock(&sThreadCountLock);                 \
  }

#define THREAD_FREEZE_POINT2_VIP()                           \
  if (freezeCountChg) {                                      \
    REAL(pthread_mutex_lock)(&sThreadCountLock);             \
    if (sNuwaReady && sIsNuwaProcess) {                      \
      pthread_mutex_unlock(&sThreadCountLock);               \
      freezePoint2 = true;                                   \
      REAL(pthread_mutex_lock)(&sThreadFreezeLock);          \
      /* Never return from the pthread_mutex_lock() call. */ \
      abort();                                               \
    }                                                        \
    sThreadFreezeCount--;                                    \
    sRecreateVIPCount--;                                     \
    pthread_cond_signal(&sThreadChangeCond);                 \
    pthread_mutex_unlock(&sThreadCountLock);                 \
  }

/**
 * Wrapping the blocking functions: epoll_wait(), poll(), pthread_mutex_lock(),
 * pthread_cond_wait() and pthread_cond_timedwait():
 *
 * These functions are wrapped by the above freeze point macros. Once a new
 * process is forked, the recreated thread will be blocked in one of the wrapper
 * functions. When recreating the thread, we longjmp() to
 * THREAD_FREEZE_POINT1() to recover the thread stack. Care must be taken to
 * maintain the semantics of the wrapped function:
 *
 * - epoll_wait() and poll(): just retry the function.
 * - pthread_mutex_lock(): don't lock if frozen at freeze point 2 (lock is
 *   already acquired).
 * - pthread_cond_wait() and pthread_cond_timedwait(): if the thread is frozen
 *   waiting the condition variable, the mutex is already released, we need to
 *   reacquire the mutex before calling the wrapped function again so the mutex
 *   will be in a valid state.
 */

extern "C" MFBT_API int
__wrap_epoll_wait(int epfd,
                  struct epoll_event *events,
                  int maxevents,
                  int timeout) {
  int rv;

  THREAD_FREEZE_POINT1();
  rv = REAL(epoll_wait)(epfd, events, maxevents, timeout);
  THREAD_FREEZE_POINT2();

  return rv;
}

extern "C" MFBT_API int
__wrap_pthread_cond_wait(pthread_cond_t *cond,
                         pthread_mutex_t *mtx) {
  int rv = 0;

  THREAD_FREEZE_POINT1_VIP();
  if (freezePoint2) {
    RECREATE_CONTINUE();
    RECREATE_PASS_VIP();
    RECREATE_GATE_VIP();
    return rv;
  }
  if (recreated && mtx) {
    if (!freezePoint1 && pthread_mutex_trylock(mtx)) {
      // The thread was frozen in pthread_cond_wait() after releasing mtx in the
      // Nuwa process. In recreating this thread, We failed to reacquire mtx
      // with the pthread_mutex_trylock() call, that is, mtx was acquired by
      // another thread. Because of this, we need the main thread's help to
      // reacquire mtx so that it will be in a valid state.
      tinfo->reacquireMutex = mtx;
    }
    RECREATE_CONTINUE();
    RECREATE_PASS_VIP();
  }
  rv = REAL(pthread_cond_wait)(cond, mtx);
  if (recreated && mtx) {
    // We still need to be gated as not to acquire another mutex associated with
    // another VIP thread and interfere with it.
    RECREATE_GATE_VIP();
  }
  THREAD_FREEZE_POINT2_VIP();

  return rv;
}

extern "C" MFBT_API int
__wrap_pthread_cond_timedwait(pthread_cond_t *cond,
                              pthread_mutex_t *mtx,
                              const struct timespec *abstime) {
  int rv = 0;

  THREAD_FREEZE_POINT1_VIP();
  if (freezePoint2) {
    RECREATE_CONTINUE();
    RECREATE_PASS_VIP();
    RECREATE_GATE_VIP();
    return rv;
  }
  if (recreated && mtx) {
    if (!freezePoint1 && pthread_mutex_trylock(mtx)) {
      tinfo->reacquireMutex = mtx;
    }
    RECREATE_CONTINUE();
    RECREATE_PASS_VIP();
  }
  rv = REAL(pthread_cond_timedwait)(cond, mtx, abstime);
  if (recreated && mtx) {
    RECREATE_GATE_VIP();
  }
  THREAD_FREEZE_POINT2_VIP();

  return rv;
}

extern "C" int __pthread_cond_timedwait(pthread_cond_t *cond,
                                        pthread_mutex_t *mtx,
                                        const struct timespec *abstime,
                                        clockid_t clock);

extern "C" MFBT_API int
__wrap___pthread_cond_timedwait(pthread_cond_t *cond,
                                pthread_mutex_t *mtx,
                                const struct timespec *abstime,
                                clockid_t clock) {
  int rv = 0;

  THREAD_FREEZE_POINT1_VIP();
  if (freezePoint2) {
    RECREATE_CONTINUE();
    RECREATE_PASS_VIP();
    RECREATE_GATE_VIP();
    return rv;
  }
  if (recreated && mtx) {
    if (!freezePoint1 && pthread_mutex_trylock(mtx)) {
      tinfo->reacquireMutex = mtx;
    }
    RECREATE_CONTINUE();
    RECREATE_PASS_VIP();
  }
  rv = REAL(__pthread_cond_timedwait)(cond, mtx, abstime, clock);
  if (recreated && mtx) {
    RECREATE_GATE_VIP();
  }
  THREAD_FREEZE_POINT2_VIP();

  return rv;
}

extern "C" MFBT_API int
__wrap_pthread_mutex_lock(pthread_mutex_t *mtx) {
  int rv = 0;

  THREAD_FREEZE_POINT1();
  if (freezePoint2) {
    return rv;
  }
  rv = REAL(pthread_mutex_lock)(mtx);
  THREAD_FREEZE_POINT2();

  return rv;
}

extern "C" MFBT_API int
__wrap_poll(struct pollfd *fds, nfds_t nfds, int timeout) {
  int rv;

  THREAD_FREEZE_POINT1();
  rv = REAL(poll)(fds, nfds, timeout);
  THREAD_FREEZE_POINT2();

  return rv;
}

extern "C" MFBT_API int
__wrap_epoll_create(int size) {
  int epollfd = REAL(epoll_create)(size);

  if (!sIsNuwaProcess) {
    return epollfd;
  }

  if (epollfd >= 0) {
    EpollManager::Singleton()->AddEpollInfo(epollfd, size);
  }

  return epollfd;
}

/**
 * Wrapping the functions to create file descriptor pairs. In the child process
 * FD pairs are created for intra-process signaling. The generation of FD pairs
 * need to be tracked in the nuwa process so they can be recreated in the
 * spawned process.
 */
struct FdPairInfo {
  enum {
    kPipe,
    kSocketpair
  } call;

  int FDs[2];
  int flags;
  int domain;
  int type;
  int protocol;
};

/**
 * Protects the access to sSingalFds.
 */
static pthread_mutex_t  sSignalFdLock = PTHREAD_MUTEX_INITIALIZER;
static std::vector<FdPairInfo> sSignalFds;

extern "C" MFBT_API int
__wrap_socketpair(int domain, int type, int protocol, int sv[2])
{
  int rv = REAL(socketpair)(domain, type, protocol, sv);

  if (!sIsNuwaProcess || rv < 0) {
    return rv;
  }

  REAL(pthread_mutex_lock)(&sSignalFdLock);
  FdPairInfo signalFd;
  signalFd.call = FdPairInfo::kSocketpair;
  signalFd.FDs[0] = sv[0];
  signalFd.FDs[1] = sv[1];
  signalFd.domain = domain;
  signalFd.type = type;
  signalFd.protocol = protocol;

  sSignalFds.push_back(signalFd);
  pthread_mutex_unlock(&sSignalFdLock);

  return rv;
}

extern "C" MFBT_API int
__wrap_pipe2(int __pipedes[2], int flags)
{
  int rv = REAL(pipe2)(__pipedes, flags);
  if (!sIsNuwaProcess || rv < 0) {
    return rv;
  }

  REAL(pthread_mutex_lock)(&sSignalFdLock);
  FdPairInfo signalFd;
  signalFd.call = FdPairInfo::kPipe;
  signalFd.FDs[0] = __pipedes[0];
  signalFd.FDs[1] = __pipedes[1];
  signalFd.flags = flags;
  sSignalFds.push_back(signalFd);
  pthread_mutex_unlock(&sSignalFdLock);
  return rv;
}

extern "C" MFBT_API int
__wrap_pipe(int __pipedes[2])
{
  return __wrap_pipe2(__pipedes, 0);
}

static void
DupeSingleFd(int newFd, int origFd)
{
  struct stat sb;
  if (fstat(origFd, &sb)) {
    // Maybe the original FD is closed.
    return;
  }
  int fd = fcntl(origFd, F_GETFD);
  int fl = fcntl(origFd, F_GETFL);
  dup2(newFd, origFd);
  fcntl(origFd, F_SETFD, fd);
  fcntl(origFd, F_SETFL, fl);
  REAL(close)(newFd);
}

extern "C" MFBT_API void
ReplaceSignalFds()
{
  for (std::vector<FdPairInfo>::iterator it = sSignalFds.begin();
       it < sSignalFds.end(); ++it) {
    int fds[2];
    int rc = 0;
    switch (it->call) {
    case FdPairInfo::kPipe:
      rc = REAL(pipe2)(fds, it->flags);
      break;
    case FdPairInfo::kSocketpair:
      rc = REAL(socketpair)(it->domain, it->type, it->protocol, fds);
      break;
    default:
      continue;
    }

    if (rc == 0) {
      DupeSingleFd(fds[0], it->FDs[0]);
      DupeSingleFd(fds[1], it->FDs[1]);
    }
  }
}

extern "C" MFBT_API int
__wrap_epoll_ctl(int aEpollFd, int aOp, int aFd, struct epoll_event *aEvent) {
  int rv = REAL(epoll_ctl)(aEpollFd, aOp, aFd, aEvent);

  if (!sIsNuwaProcess || rv == -1) {
    return rv;
  }

  EpollManager::EpollInfo *info =
    EpollManager::Singleton()->FindEpollInfo(aEpollFd);
  if (info == NULL) {
    abort();
  }

  switch(aOp) {
  case EPOLL_CTL_ADD:
    info->AddEvents(aFd, *aEvent);
    break;

  case EPOLL_CTL_MOD:
    info->ModifyEvents(aFd, *aEvent);
    break;

  case EPOLL_CTL_DEL:
    info->RemoveEvents(aFd);
    break;

  default:
    abort();
  }

  return rv;
}

// XXX: thinker: Maybe, we should also track dup, dup2, and other functions.
extern "C" MFBT_API int
__wrap_close(int aFd) {
  int rv = REAL(close)(aFd);
  if (!sIsNuwaProcess || rv == -1) {
    return rv;
  }

  EpollManager::EpollInfo *info =
    EpollManager::Singleton()->FindEpollInfo(aFd);
  if (info) {
    EpollManager::Singleton()->RemoveEpollInfo(aFd);
  }

  return rv;
}

static void *
thread_recreate_startup(void *arg) {
  /*
   * Dark Art!! Never do the same unless you are ABSOLUTELY sure what you are
   * doing!
   *
   * The stack space collapsed by this frame had been reserved by
   * thread_create_startup().  And thread_create_startup() will
   * return immediately after returning from real start routine, so
   * all collapsed values does not affect the result.
   *
   * All outer frames of thread_create_startup() and
   * thread_recreate_startup() are equivalent, so
   * thread_create_startup() will return successfully.
   */
  thread_info_t *tinfo = (thread_info_t *)arg;

  RestoreTLSInfo(tinfo);

  if (setjmp(tinfo->retEnv) != 0) {
    return NULL;
  }

  // longjump() to recreate the stack on the new thread.
  longjmp(tinfo->jmpEnv, 1);

  // Never go here!
  abort();

  return NULL;
}

/**
 * Recreate the context given by tinfo at a new thread.
 */
static void
thread_recreate(thread_info_t *tinfo) {
  pthread_t thread;

  // Note that the thread_recreate_startup() runs on the stack specified by
  // tinfo.
  pthread_create(&thread, &tinfo->threadAttr, thread_recreate_startup, tinfo);
}

/**
 * Recreate all threads in a process forked from an Nuwa process.
 */
static void
RecreateThreads() {
  sIsNuwaProcess = false;
  sIsFreezing = false;

  // Run registered constructors.
  for (std::vector<nuwa_construct_t>::iterator ctr = sConstructors.begin();
       ctr != sConstructors.end();
       ctr++) {
    (*ctr).construct((*ctr).arg);
  }
  sConstructors.clear();

  REAL(pthread_mutex_lock)(&sThreadCountLock);
  thread_info_t *tinfo = sAllThreads.getFirst();
  pthread_mutex_unlock(&sThreadCountLock);

  RECREATE_START();
  while (tinfo != NULL) {
    if (tinfo->flags & TINFO_FLAG_NUWA_SUPPORT) {
      RECREATE_BEFORE(tinfo);
      thread_recreate(tinfo);
      RECREATE_WAIT();
      if (tinfo->reacquireMutex) {
        REAL(pthread_mutex_lock)(tinfo->reacquireMutex);
      }
    } else if(!(tinfo->flags & TINFO_FLAG_NUWA_SKIP)) {
      // An unmarked thread is found other than the main thread.

      // All threads should be marked as one of SUPPORT or SKIP, or
      // abort the process to make sure all threads in the Nuwa
      // process are Nuwa-aware.
      abort();
    }

    tinfo = tinfo->getNext();
  }
  RECREATE_WAIT_ALL_VIP();
  RECREATE_OPEN_GATE();

  RECREATE_FINISH();

  // Run registered final constructors.
  for (std::vector<nuwa_construct_t>::iterator ctr = sFinalConstructors.begin();
       ctr != sFinalConstructors.end();
       ctr++) {
    (*ctr).construct((*ctr).arg);
  }
  sFinalConstructors.clear();
}

extern "C" {

/**
 * Recreate all epoll fds and restore status; include all events.
 */
static void
RecreateEpollFds() {
  EpollManager *man = EpollManager::Singleton();

  for (EpollManager::const_iterator info_it = man->begin();
       info_it != man->end();
       info_it++) {
    int epollfd = info_it->first;
    const EpollManager::EpollInfo *info = &info_it->second;

    int fdflags = fcntl(epollfd, F_GETFD);
    if (fdflags == -1) {
      abort();
    }
    int fl = fcntl(epollfd, F_GETFL);
    if (fl == -1) {
      abort();
    }

    int newepollfd = REAL(epoll_create)(info->BackSize());
    if (newepollfd == -1) {
      abort();
    }
    int rv = REAL(close)(epollfd);
    if (rv == -1) {
      abort();
    }
    rv = dup2(newepollfd, epollfd);
    if (rv == -1) {
      abort();
    }
    rv = REAL(close)(newepollfd);
    if (rv == -1) {
      abort();
    }

    rv = fcntl(epollfd, F_SETFD, fdflags);
    if (rv == -1) {
      abort();
    }
    rv = fcntl(epollfd, F_SETFL, fl);
    if (rv == -1) {
      abort();
    }

    for (EpollManager::EpollInfo::const_iterator events_it = info->begin();
         events_it != info->end();
         events_it++) {
      int fd = events_it->first;
      epoll_event events;
      events = events_it->second;
      rv = REAL(epoll_ctl)(epollfd, EPOLL_CTL_ADD, fd, &events);
      if (rv == -1) {
        abort();
      }
    }
  }

  // Shutdown EpollManager. It won't be needed in the spawned process.
  EpollManager::Shutdown();
}

/**
 * Fix IPC to make it ready.
 *
 * Especially, fix ContentChild.
 */
static void
ReplaceIPC(NuwaProtoFdInfo *aInfoList, int aInfoSize) {
  int i;
  int rv;

  for (i = 0; i < aInfoSize; i++) {
    int fd = fcntl(aInfoList[i].originFd, F_GETFD);
    if (fd == -1) {
      abort();
    }

    int fl = fcntl(aInfoList[i].originFd, F_GETFL);
    if (fl == -1) {
      abort();
    }

    rv = dup2(aInfoList[i].newFds[NUWA_NEWFD_CHILD], aInfoList[i].originFd);
    if (rv == -1) {
      abort();
    }

    rv = fcntl(aInfoList[i].originFd, F_SETFD, fd);
    if (rv == -1) {
      abort();
    }

    rv = fcntl(aInfoList[i].originFd, F_SETFL, fl);
    if (rv == -1) {
      abort();
    }
  }
}

/**
 * Add a new content process at the chrome process.
 */
static void
AddNewProcess(pid_t pid, NuwaProtoFdInfo *aInfoList, int aInfoSize) {
  static bool (*AddNewIPCProcess)(pid_t, NuwaProtoFdInfo *, int) = NULL;

  if (AddNewIPCProcess == NULL) {
    AddNewIPCProcess = (bool (*)(pid_t, NuwaProtoFdInfo *, int))
      dlsym(RTLD_DEFAULT, "AddNewIPCProcess");
  }
  AddNewIPCProcess(pid, aInfoList, aInfoSize);
}

static void
PrepareProtoSockets(NuwaProtoFdInfo *aInfoList, int aInfoSize) {
  int i;
  int rv;

  for (i = 0; i < aInfoSize; i++) {
    rv = REAL(socketpair)(PF_UNIX, SOCK_STREAM, 0, aInfoList[i].newFds);
    if (rv == -1) {
      abort();
    }
  }
}

static void
CloseAllProtoSockets(NuwaProtoFdInfo *aInfoList, int aInfoSize) {
  int i;

  for (i = 0; i < aInfoSize; i++) {
    REAL(close)(aInfoList[i].newFds[0]);
    REAL(close)(aInfoList[i].newFds[1]);
  }
}

/**
 * Fork a new process that is ready for running IPC.
 *
 * @return the PID of the new process.
 */
static int
ForkIPCProcess() {
  int pid;

  REAL(pthread_mutex_lock)(&sForkLock);

  PrepareProtoSockets(sProtoFdInfos, sProtoFdInfosSize);

  sNuwaForking = true;
  pid = fork();
  sNuwaForking = false;
  if (pid == -1) {
    abort();
  }

  if (pid > 0) {
    // in the parent
    AddNewProcess(pid, sProtoFdInfos, sProtoFdInfosSize);
    CloseAllProtoSockets(sProtoFdInfos, sProtoFdInfosSize);
  } else {
    // in the child
#ifdef NUWA_DEBUG_CHILD_PROCESS
    fprintf(stderr, "\n\n DEBUG ME @%d\n\n", getpid());
    sleep(15);
#endif
    ReplaceSignalFds();
    ReplaceIPC(sProtoFdInfos, sProtoFdInfosSize);
    RecreateEpollFds();
    RecreateThreads();
    CloseAllProtoSockets(sProtoFdInfos, sProtoFdInfosSize);
  }

  sForkWaitCondChanged = true;
  pthread_cond_signal(&sForkWaitCond);
  pthread_mutex_unlock(&sForkLock);

  return pid;
}

/**
 * Prepare for spawning a new process. Called on the IPC thread.
 */
MFBT_API void
NuwaSpawnPrepare() {
  REAL(pthread_mutex_lock)(&sForkLock);

  sForkWaitCondChanged = false; // Will be modified on the main thread.
}

/**
 * Let IPC thread wait until fork action on the main thread has completed.
 */
MFBT_API void
NuwaSpawnWait() {
  while (!sForkWaitCondChanged) {
    REAL(pthread_cond_wait)(&sForkWaitCond, &sForkLock);
  }
  pthread_mutex_unlock(&sForkLock);
}

/**
 * Spawn a new process. If not ready for spawn (still waiting for some threads
 * to freeze), postpone the spawn request until ready.
 *
 * @return the pid of the new process, or 0 if not ready.
 */
MFBT_API pid_t
NuwaSpawn() {
  if (gettid() != getpid()) {
    // Not the main thread.
    abort();
  }

  pid_t pid = 0;

  if (sNuwaReady) {
    pid = ForkIPCProcess();
  } else {
    sNuwaPendingSpawn = true;
  }

  return pid;
}

/**
 * Prepare to freeze the Nuwa-supporting threads.
 */
MFBT_API void
PrepareNuwaProcess() {
  sIsNuwaProcess = true;
  // Explicitly ignore SIGCHLD so we don't have to call watpid() to reap
  // dead child processes.
  signal(SIGCHLD, SIG_IGN);

  // Make marked threads block in one freeze point.
  REAL(pthread_mutex_lock)(&sThreadFreezeLock);
}

// Make current process as a Nuwa process.
MFBT_API void
MakeNuwaProcess() {
  void (*GetProtoFdInfos)(NuwaProtoFdInfo *, int, int *) = NULL;
  void (*OnNuwaProcessReady)() = NULL;
  sIsFreezing = true;

  REAL(pthread_mutex_lock)(&sThreadCountLock);

  // wait until all threads are frozen.
  while ((sThreadFreezeCount + sThreadSkipCount) != sThreadCount) {
    REAL(pthread_cond_wait)(&sThreadChangeCond, &sThreadCountLock);
  }

  GetProtoFdInfos = (void (*)(NuwaProtoFdInfo *, int, int *))
    dlsym(RTLD_DEFAULT, "GetProtoFdInfos");
  GetProtoFdInfos(sProtoFdInfos, NUWA_TOPLEVEL_MAX, &sProtoFdInfosSize);

  sNuwaReady = true;

  pthread_mutex_unlock(&sThreadCountLock);

  OnNuwaProcessReady = (void (*)())dlsym(RTLD_DEFAULT, "OnNuwaProcessReady");
  OnNuwaProcessReady();

  if (sNuwaPendingSpawn) {
    sNuwaPendingSpawn = false;
    NuwaSpawn();
  }
}

/**
 * Mark the current thread as supporting Nuwa. The thread will be recreated in
 * the spawned process.
 */
MFBT_API void
NuwaMarkCurrentThread(void (*recreate)(void *), void *arg) {
  if (!sIsNuwaProcess) {
    return;
  }

  thread_info_t *tinfo = CUR_THREAD_INFO;
  if (tinfo == NULL) {
    abort();
  }

  tinfo->flags |= TINFO_FLAG_NUWA_SUPPORT;
  tinfo->recrFunc = recreate;
  tinfo->recrArg = arg;
}

/**
 * Mark the current thread as not supporting Nuwa. Don't recreate this thread in
 * the spawned process.
 */
MFBT_API void
NuwaSkipCurrentThread() {
  if (!sIsNuwaProcess) return;

  thread_info_t *tinfo = CUR_THREAD_INFO;
  if (tinfo == NULL) {
    abort();
  }

  if (!(tinfo->flags & TINFO_FLAG_NUWA_SKIP)) {
    sThreadSkipCount++;
  }
  tinfo->flags |= TINFO_FLAG_NUWA_SKIP;
}

/**
 * Force to freeze the current thread.
 *
 * This method does not return in Nuwa process.  It returns for the
 * recreated thread.
 */
MFBT_API void
NuwaFreezeCurrentThread() {
  thread_info_t *tinfo = CUR_THREAD_INFO;
  if (sIsNuwaProcess &&
      (tinfo = CUR_THREAD_INFO) &&
      (tinfo->flags & TINFO_FLAG_NUWA_SUPPORT)) {
    if (!setjmp(tinfo->jmpEnv)) {
      REAL(pthread_mutex_lock)(&sThreadCountLock);
      SaveTLSInfo(tinfo);
      sThreadFreezeCount++;
      pthread_cond_signal(&sThreadChangeCond);
      pthread_mutex_unlock(&sThreadCountLock);

      REAL(pthread_mutex_lock)(&sThreadFreezeLock);
    } else {
      RECREATE_CONTINUE();
      RECREATE_GATE();
    }
  }
}

/**
 * The caller of NuwaCheckpointCurrentThread() is at the line it wishes to
 * return after the thread is recreated.
 *
 * The checkpointed thread will restart at the calling line of
 * NuwaCheckpointCurrentThread(). This macro returns true in the Nuwa process
 * and false on the recreated thread in the forked process.
 *
 * NuwaCheckpointCurrentThread() is implemented as a macro so we can place the
 * setjmp() call in the calling method without changing its stack pointer. This
 * is essential for not corrupting the stack when the calling thread continues
 * to request the main thread for forking a new process. The caller of
 * NuwaCheckpointCurrentThread() should not return before the process forking
 * finishes.
 *
 * @return true for Nuwa process, and false in the forked process.
 */
MFBT_API jmp_buf*
NuwaCheckpointCurrentThread1() {
  thread_info_t *tinfo = CUR_THREAD_INFO;
  if (sIsNuwaProcess &&
      (tinfo = CUR_THREAD_INFO) &&
      (tinfo->flags & TINFO_FLAG_NUWA_SUPPORT)) {
    return &tinfo->jmpEnv;
  }
  abort();
  return nullptr;
}

MFBT_API bool
NuwaCheckpointCurrentThread2(int setjmpCond) {
  thread_info_t *tinfo = CUR_THREAD_INFO;
  if (setjmpCond == 0) {
    REAL(pthread_mutex_lock)(&sThreadCountLock);
    if (!(tinfo->flags & TINFO_FLAG_NUWA_EXPLICIT_CHECKPOINT)) {
      tinfo->flags |= TINFO_FLAG_NUWA_EXPLICIT_CHECKPOINT;
      SaveTLSInfo(tinfo);
      sThreadFreezeCount++;
    }
    pthread_cond_signal(&sThreadChangeCond);
    pthread_mutex_unlock(&sThreadCountLock);
    return true;
  }
  RECREATE_CONTINUE();
  RECREATE_GATE();
  return false;               // Recreated thread.
}

/**
 * Register methods to be invoked before recreating threads in the spawned
 * process.
 */
MFBT_API void
NuwaAddConstructor(void (*construct)(void *), void *arg) {
  nuwa_construct_t ctr;
  ctr.construct = construct;
  ctr.arg = arg;
  sConstructors.push_back(ctr);
}

/**
 * Register methods to be invoked after recreating threads in the spawned
 * process.
 */
MFBT_API void
NuwaAddFinalConstructor(void (*construct)(void *), void *arg) {
  nuwa_construct_t ctr;
  ctr.construct = construct;
  ctr.arg = arg;
  sFinalConstructors.push_back(ctr);
}

/**
 * @return if the current process is the nuwa process.
 */
MFBT_API bool
IsNuwaProcess() {
  return sIsNuwaProcess;
}

/**
 * @return if the nuwa process is ready for spawning new processes.
 */
MFBT_API bool
IsNuwaReady() {
  return sNuwaReady;
}

}      // extern "C"