Bug 856331 - Make breakpad unwinding runtime switchable. r=jseward

--HG--
extra : rebase_source : 1094beb17115a0d0e4d27eeb848c3932dfe0b2b0

tools/profiler/BreakpadSampler.cpp

@@ -156,7 +156,7 @@ void genPseudoBacktraceEntries(/*MODIFIED*/UnwinderThreadBuffer* utb,
 }
 
 // RUNS IN SIGHANDLER CONTEXT
-void BreakpadSampler::Tick(TickSample* sample)
+void TableTicker::UnwinderTick(TickSample* sample)
 {
   if (!sample->threadProfile) {
     // Platform doesn't support multithread, so use the main thread profile we created

tools/profiler/TableTicker.cpp

@@ -392,6 +392,15 @@ void doSampleStackTrace(PseudoStack *aStack, ThreadProfile &aProfile, TickSample
 }
 
 void TableTicker::Tick(TickSample* sample)
+{
+  if (HasUnwinderThread()) {
+    UnwinderTick(sample);
+  } else {
+    InplaceTick(sample);
+  }
+}
+
+void TableTicker::InplaceTick(TickSample* sample)
 {
   ThreadProfile& currThreadProfile = *sample->threadProfile;
 

tools/profiler/TableTicker.h

@@ -32,6 +32,7 @@ class TableTicker: public Sampler {
     , mPrimaryThreadProfile(nullptr)
     , mStartTime(TimeStamp::Now())
     , mSaveRequested(false)
+    , mUnwinderThread(false)
   {
     mUseStackWalk = hasFeature(aFeatures, aFeatureCount, "stackwalk");
 
@@ -39,6 +40,7 @@ class TableTicker: public Sampler {
     mJankOnly = hasFeature(aFeatures, aFeatureCount, "jank");
     mProfileJS = hasFeature(aFeatures, aFeatureCount, "js");
     mProfileThreads = true || hasFeature(aFeatures, aFeatureCount, "threads");
+    mUnwinderThread = hasFeature(aFeatures, aFeatureCount, "unwinder") || sps_version2();
     mAddLeafAddresses = hasFeature(aFeatures, aFeatureCount, "leaf");
 
     {
@@ -119,12 +121,17 @@ class TableTicker: public Sampler {
   virtual JSObject *ToJSObject(JSContext *aCx);
   JSCustomObject *GetMetaJSCustomObject(JSAObjectBuilder& b);
 
+  bool HasUnwinderThread() const { return mUnwinderThread; }
   bool ProfileJS() const { return mProfileJS; }
   bool ProfileThreads() const { return mProfileThreads; }
 
-  virtual BreakpadSampler* AsBreakpadSampler() { return nullptr; }
-
 protected:
+  // Called within a signal. This function must be reentrant
+  virtual void UnwinderTick(TickSample* sample);
+
+  // Called within a signal. This function must be reentrant
+  virtual void InplaceTick(TickSample* sample);
+
   // Not implemented on platforms which do not support backtracing
   void doNativeBacktrace(ThreadProfile &aProfile, TickSample* aSample);
 
@@ -139,18 +146,6 @@ protected:
   bool mJankOnly;
   bool mProfileJS;
   bool mProfileThreads;
-};
-
-class BreakpadSampler: public TableTicker {
- public:
-  BreakpadSampler(int aInterval, int aEntrySize,
-              const char** aFeatures, uint32_t aFeatureCount)
-    : TableTicker(aInterval, aEntrySize, aFeatures, aFeatureCount)
-  {}
-
-  // Called within a signal. This function must be reentrant
-  virtual void Tick(TickSample* sample);
-
-  virtual BreakpadSampler* AsBreakpadSampler() { return this; }
+  bool mUnwinderThread;
 };
 

tools/profiler/UnwinderThread2.cpp

@@ -71,6 +71,10 @@ void uwt__init()
 {
 }
 
+void uwt__stop()
+{
+}
+
 void uwt__deinit()
 {
 }
@@ -153,13 +157,17 @@ void uwt__init()
   MOZ_ALWAYS_TRUE(r==0);
 }
 
-void uwt__deinit()
+void uwt__stop()
 {
   // Shut down the unwinder thread.
   MOZ_ASSERT(unwind_thr_exit_now == 0);
   unwind_thr_exit_now = 1;
   do_MBAR();
   int r = pthread_join(unwind_thr, NULL); MOZ_ALWAYS_TRUE(r==0);
+}
+
+void uwt__deinit()
+{
   do_breakpad_unwind_Buffer_free_singletons();
 }
 
@@ -817,14 +825,9 @@ static void* unwind_thr_fn(void* exit_nowV)
     MOZ_ASSERT(buffers);
     int i;
     for (i = 0; i < N_UNW_THR_BUFFERS; i++) {
-      /* These calloc-ations are never freed, even when the unwinder
-         thread is shut down.  The reason is that sampler threads
-         might still be filling them up even after this thread is shut
-         down.  The buffers themselves are not protected by the
-         spinlock, so we have no way to stop them being accessed
-         whilst we free them.  It doesn't matter much since they will
-         not be reallocated if a new unwinder thread is restarted
-         later. */
+      /* These calloc-ations are shared between the sampler and the unwinder.
+       * They must be free after both threads have terminated.
+       */
       buffers[i] = (UnwinderThreadBuffer*)
                    calloc(sizeof(UnwinderThreadBuffer), 1);
       MOZ_ASSERT(buffers[i]);
@@ -872,7 +875,10 @@ static void* unwind_thr_fn(void* exit_nowV)
 
   while (1) {
 
-    if (*exit_now != 0) break;
+    if (*exit_now != 0) {
+      *exit_now = 0;
+      break;
+    }
 
     spinLock_acquire(&g_spinLock);
 
@@ -1528,6 +1534,11 @@ void do_breakpad_unwind_Buffer_free_singletons()
     delete sModules;
     sModules = NULL;
   }
+
+  g_stackLimitsUsed = 0;
+  g_seqNo = 0;
+  free(g_buffers);
+  g_buffers = NULL;
 }
 
 static

tools/profiler/UnwinderThread2.h

@@ -28,6 +28,13 @@ void utb__addEntry(/*MOD*/UnwinderThreadBuffer* utb,
 void uwt__init();
 
 // Request the unwinder thread to exit, and wait until it has done so.
+// This must be called before stopping the profiler because we hold a
+// reference to the profile which is owned by the profiler.
+void uwt__stop();
+
+// Release the unwinder resources. This must be called after profiling
+// has stop. At this point we know the profiler doesn't hold any buffer
+// and can safely release any resources.
 void uwt__deinit();
 
 // Registers a sampler thread for profiling.  Threads must be registered

tools/profiler/platform-macos.cc

@@ -121,18 +121,6 @@ static void SetThreadName(const char* name) {
 
 static void* ThreadEntry(void* arg) {
   Thread* thread = reinterpret_cast<Thread*>(arg);
-  // This is also initialized by the first argument to pthread_create() but we
-  // don't know which thread will run first (the original thread or the new
-  // one) so we initialize it here too.
-
-  // BEGIN temp hack for SPS v1-vs-v2
-  extern bool sps_version2();
-  if (sps_version2()) {
-    // Register this thread for profiling.
-    int aLocal;
-    uwt__register_thread_for_profiling( &aLocal );
-  }
-  // END temp hack for SPS v1-vs-v2
 
   thread->thread_ = pthread_self();
   SetThreadName(thread->name());

tools/profiler/platform.cpp

@@ -268,27 +268,10 @@ void mozilla_sampler_init()
 
   Sampler::RegisterCurrentThread("Gecko", stack, true);
 
-  if (sps_version2()) {
-    // Read mode settings from MOZ_PROFILER_MODE and interval
-    // settings from MOZ_PROFILER_INTERVAL and stack-scan threshhold
-    // from MOZ_PROFILER_STACK_SCAN.
-    read_profiler_env_vars();
-
-    // Create the unwinder thread.  ATM there is only one.
-    uwt__init();
-
-# if defined(SPS_PLAT_amd64_linux) || defined(SPS_PLAT_arm_android) \
-     || defined(SPS_PLAT_x86_linux) || defined(SPS_PLAT_x86_android) \
-     || defined(SPS_PLAT_x86_windows) || defined(SPS_PLAT_amd64_windows) /* no idea if windows is correct */
-    // On Linuxes, register this thread (temporarily) for profiling
-    int aLocal;
-    uwt__register_thread_for_profiling( &aLocal );
-# elif defined(SPS_PLAT_amd64_darwin) || defined(SPS_PLAT_x86_darwin)
-    // Registration is done in platform-macos.cc
-# else
-#   error "Unknown plat"
-# endif
-  }
+  // Read mode settings from MOZ_PROFILER_MODE and interval
+  // settings from MOZ_PROFILER_INTERVAL and stack-scan threshhold
+  // from MOZ_PROFILER_STACK_SCAN.
+  read_profiler_env_vars();
 
   // Allow the profiler to be started using signals
   OS::RegisterStartHandler();
@@ -333,14 +316,6 @@ void mozilla_sampler_shutdown()
     }
   }
 
-  // Shut down and reap the unwinder thread.  We have to do this
-  // before stopping the sampler, so as to guarantee that the unwinder
-  // thread doesn't try to access memory that the subsequent call to
-  // mozilla_sampler_stop causes to be freed.
-  if (sps_version2()) {
-    uwt__deinit();
-  }
-
   profiler_stop();
 
   Sampler::Shutdown();
@@ -396,13 +371,24 @@ const char** mozilla_sampler_get_features()
 {
   static const char* features[] = {
 #if defined(MOZ_PROFILING) && defined(HAVE_NATIVE_UNWIND)
+    // Walk the C++ stack.
     "stackwalk",
 #endif
 #if defined(ENABLE_SPS_LEAF_DATA)
+    // Include the C++ leaf node if not stackwalking. DevTools
+    // profiler doesn't want the native addresses.
     "leaf",
 #endif
+#if !defined(SPS_OS_windows)
+    // Use a seperate thread of walking the stack.
+    "unwinder",
+#endif
+    // Only record samples during periods of bad responsiveness
     "jank",
+    // Tell the JS engine to emmit pseudostack entries in the
+    // pro/epilogue.
     "js",
+    // Profile the registered secondary threads.
     "threads",
     NULL
   };
@@ -432,15 +418,17 @@ void mozilla_sampler_start(int aProfileEntries, int aInterval,
   profiler_stop();
 
   TableTicker* t;
-  if (sps_version2()) {
-    t = new BreakpadSampler(aInterval ? aInterval : PROFILE_DEFAULT_INTERVAL,
-                           aProfileEntries ? aProfileEntries : PROFILE_DEFAULT_ENTRY,
-                           aFeatures, aFeatureCount);
-  } else {
-    t = new TableTicker(aInterval ? aInterval : PROFILE_DEFAULT_INTERVAL,
-                        aProfileEntries ? aProfileEntries : PROFILE_DEFAULT_ENTRY,
-                        aFeatures, aFeatureCount);
+  t = new TableTicker(aInterval ? aInterval : PROFILE_DEFAULT_INTERVAL,
+                      aProfileEntries ? aProfileEntries : PROFILE_DEFAULT_ENTRY,
+                      aFeatures, aFeatureCount);
+  if (t->HasUnwinderThread()) {
+    int aLocal;
+    uwt__register_thread_for_profiling( &aLocal );
+
+    // Create the unwinder thread.  ATM there is only one.
+    uwt__init();
   }
+
   tlsTicker.set(t);
   t->Start();
   if (t->ProfileJS()) {
@@ -475,6 +463,15 @@ void mozilla_sampler_stop()
   }
 
   bool disableJS = t->ProfileJS();
+  bool unwinderThreader = t->HasUnwinderThread();
+
+  // Shut down and reap the unwinder thread.  We have to do this
+  // before stopping the sampler, so as to guarantee that the unwinder
+  // thread doesn't try to access memory that the subsequent call to
+  // mozilla_sampler_stop causes to be freed.
+  if (unwinderThreader) {
+    uwt__stop();
+  }
 
   t->Stop();
   delete t;
@@ -485,6 +482,10 @@ void mozilla_sampler_stop()
   if (disableJS)
     stack->disableJSSampling();
 
+  if (unwinderThreader) {
+    uwt__deinit();
+  }
+
   sIsProfiling = false;
 
   nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();