gecko/xpcom/threads/nsThread.cpp

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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla code.
*
* The Initial Developer of the Original Code is Google Inc.
* Portions created by the Initial Developer are Copyright (C) 2006
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Darin Fisher <darin@meer.net>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#include "mozilla/Monitor.h"
#include "nsThread.h"
#include "nsThreadManager.h"
#include "nsIClassInfoImpl.h"
#include "nsIProgrammingLanguage.h"
#include "nsAutoPtr.h"
#include "nsCOMPtr.h"
#include "prlog.h"
#include "nsThreadUtilsInternal.h"
#define HAVE_UALARM _BSD_SOURCE || (_XOPEN_SOURCE >= 500 || \
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) && \
!(_POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 700)
#if defined(XP_UNIX) && !defined(ANDROID) && !defined(DEBUG) && HAVE_UALARM \
&& defined(_GNU_SOURCE)
# define MOZ_CANARY
# include <unistd.h>
# include <execinfo.h>
# include <signal.h>
# include <fcntl.h>
# include "nsXULAppAPI.h"
#endif
#include "mozilla/FunctionTimer.h"
#if defined(NS_FUNCTION_TIMER) && defined(_MSC_VER)
#include "nsTimerImpl.h"
#include "nsStackWalk.h"
#endif
#ifdef NS_FUNCTION_TIMER
#include "nsCRT.h"
#endif
using namespace mozilla;
#ifdef PR_LOGGING
static PRLogModuleInfo *sLog = PR_NewLogModule("nsThread");
#endif
#define LOG(args) PR_LOG(sLog, PR_LOG_DEBUG, args)
NS_DECL_CI_INTERFACE_GETTER(nsThread)
nsIThreadObserver* nsThread::sGlobalObserver;
//-----------------------------------------------------------------------------
// Because we do not have our own nsIFactory, we have to implement nsIClassInfo
// somewhat manually.
class nsThreadClassInfo : public nsIClassInfo {
public:
NS_DECL_ISUPPORTS_INHERITED // no mRefCnt
NS_DECL_NSICLASSINFO
nsThreadClassInfo() {}
};
static nsThreadClassInfo sThreadClassInfo;
NS_IMETHODIMP_(nsrefcnt) nsThreadClassInfo::AddRef() { return 2; }
NS_IMETHODIMP_(nsrefcnt) nsThreadClassInfo::Release() { return 1; }
NS_IMPL_QUERY_INTERFACE1(nsThreadClassInfo, nsIClassInfo)
NS_IMETHODIMP
nsThreadClassInfo::GetInterfaces(PRUint32 *count, nsIID ***array)
{
return NS_CI_INTERFACE_GETTER_NAME(nsThread)(count, array);
}
NS_IMETHODIMP
nsThreadClassInfo::GetHelperForLanguage(PRUint32 lang, nsISupports **result)
{
*result = nsnull;
return NS_OK;
}
NS_IMETHODIMP
nsThreadClassInfo::GetContractID(char **result)
{
*result = nsnull;
return NS_OK;
}
NS_IMETHODIMP
nsThreadClassInfo::GetClassDescription(char **result)
{
*result = nsnull;
return NS_OK;
}
NS_IMETHODIMP
nsThreadClassInfo::GetClassID(nsCID **result)
{
*result = nsnull;
return NS_OK;
}
NS_IMETHODIMP
nsThreadClassInfo::GetImplementationLanguage(PRUint32 *result)
{
*result = nsIProgrammingLanguage::CPLUSPLUS;
return NS_OK;
}
NS_IMETHODIMP
nsThreadClassInfo::GetFlags(PRUint32 *result)
{
*result = THREADSAFE;
return NS_OK;
}
NS_IMETHODIMP
nsThreadClassInfo::GetClassIDNoAlloc(nsCID *result)
{
return NS_ERROR_NOT_AVAILABLE;
}
//-----------------------------------------------------------------------------
NS_IMPL_THREADSAFE_ADDREF(nsThread)
NS_IMPL_THREADSAFE_RELEASE(nsThread)
NS_INTERFACE_MAP_BEGIN(nsThread)
NS_INTERFACE_MAP_ENTRY(nsIThread)
NS_INTERFACE_MAP_ENTRY(nsIThreadInternal)
NS_INTERFACE_MAP_ENTRY(nsIThreadInternal2)
NS_INTERFACE_MAP_ENTRY(nsIEventTarget)
NS_INTERFACE_MAP_ENTRY(nsISupportsPriority)
NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIThread)
if (aIID.Equals(NS_GET_IID(nsIClassInfo))) {
foundInterface = static_cast<nsIClassInfo*>(&sThreadClassInfo);
} else
NS_INTERFACE_MAP_END
NS_IMPL_CI_INTERFACE_GETTER4(nsThread, nsIThread, nsIThreadInternal,
nsIEventTarget, nsISupportsPriority)
//-----------------------------------------------------------------------------
class nsThreadStartupEvent : public nsRunnable {
public:
// Create a new thread startup object.
static nsThreadStartupEvent *Create() {
return new nsThreadStartupEvent();
}
// This method does not return until the thread startup object is in the
// completion state.
void Wait() {
if (mInitialized) // Maybe avoid locking...
return;
MonitorAutoEnter mon(mMon);
while (!mInitialized)
mon.Wait();
}
// This method needs to be public to support older compilers (xlC_r on AIX).
// It should be called directly as this class type is reference counted.
virtual ~nsThreadStartupEvent() {
}
private:
NS_IMETHOD Run() {
MonitorAutoEnter mon(mMon);
mInitialized = PR_TRUE;
mon.Notify();
return NS_OK;
}
nsThreadStartupEvent()
: mMon("nsThreadStartupEvent.mMon")
, mInitialized(PR_FALSE) {
}
Monitor mMon;
PRBool mInitialized;
};
//-----------------------------------------------------------------------------
struct nsThreadShutdownContext {
nsThread *joiningThread;
PRBool shutdownAck;
};
// This event is responsible for notifying nsThread::Shutdown that it is time
// to call PR_JoinThread.
class nsThreadShutdownAckEvent : public nsRunnable {
public:
nsThreadShutdownAckEvent(nsThreadShutdownContext *ctx)
: mShutdownContext(ctx) {
}
NS_IMETHOD Run() {
mShutdownContext->shutdownAck = PR_TRUE;
return NS_OK;
}
private:
nsThreadShutdownContext *mShutdownContext;
};
// This event is responsible for setting mShutdownContext
class nsThreadShutdownEvent : public nsRunnable {
public:
nsThreadShutdownEvent(nsThread *thr, nsThreadShutdownContext *ctx)
: mThread(thr), mShutdownContext(ctx) {
}
NS_IMETHOD Run() {
mThread->mShutdownContext = mShutdownContext;
return NS_OK;
}
private:
nsRefPtr<nsThread> mThread;
nsThreadShutdownContext *mShutdownContext;
};
//-----------------------------------------------------------------------------
/*static*/ void
nsThread::ThreadFunc(void *arg)
{
nsThread *self = static_cast<nsThread *>(arg); // strong reference
self->mThread = PR_GetCurrentThread();
// Inform the ThreadManager
nsThreadManager::get()->RegisterCurrentThread(self);
// Wait for and process startup event
nsCOMPtr<nsIRunnable> event;
if (!self->GetEvent(PR_TRUE, getter_AddRefs(event))) {
NS_WARNING("failed waiting for thread startup event");
return;
}
event->Run(); // unblocks nsThread::Init
event = nsnull;
// Now, process incoming events...
while (!self->ShuttingDown())
NS_ProcessNextEvent(self);
// Do NS_ProcessPendingEvents but with special handling to set
// mEventsAreDoomed atomically with the removal of the last event. The key
// invariant here is that we will never permit PutEvent to succeed if the
// event would be left in the queue after our final call to
// NS_ProcessPendingEvents.
while (PR_TRUE) {
{
MutexAutoLock lock(self->mLock);
if (!self->mEvents->HasPendingEvent()) {
// No events in the queue, so we will stop now. Don't let any more
// events be added, since they won't be processed. It is critical
// that no PutEvent can occur between testing that the event queue is
// empty and setting mEventsAreDoomed!
self->mEventsAreDoomed = PR_TRUE;
break;
}
}
NS_ProcessPendingEvents(self);
}
// Inform the threadmanager that this thread is going away
nsThreadManager::get()->UnregisterCurrentThread(self);
// Dispatch shutdown ACK
event = new nsThreadShutdownAckEvent(self->mShutdownContext);
self->mShutdownContext->joiningThread->Dispatch(event, NS_DISPATCH_NORMAL);
// Release any observer of the thread here.
self->SetObserver(nsnull);
NS_RELEASE(self);
}
//-----------------------------------------------------------------------------
nsThread::nsThread()
: mLock("nsThread.mLock")
, mEvents(&mEventsRoot)
, mPriority(PRIORITY_NORMAL)
, mThread(nsnull)
, mRunningEvent(0)
, mShutdownContext(nsnull)
, mShutdownRequired(PR_FALSE)
, mEventsAreDoomed(PR_FALSE)
{
}
nsThread::~nsThread()
{
}
nsresult
nsThread::Init()
{
// spawn thread and wait until it is fully setup
nsRefPtr<nsThreadStartupEvent> startup = nsThreadStartupEvent::Create();
NS_ENSURE_TRUE(startup, NS_ERROR_OUT_OF_MEMORY);
NS_ADDREF_THIS();
mShutdownRequired = PR_TRUE;
// ThreadFunc is responsible for setting mThread
PRThread *thr = PR_CreateThread(PR_USER_THREAD, ThreadFunc, this,
PR_PRIORITY_NORMAL, PR_GLOBAL_THREAD,
PR_JOINABLE_THREAD, 0);
if (!thr) {
NS_RELEASE_THIS();
return NS_ERROR_OUT_OF_MEMORY;
}
// ThreadFunc will wait for this event to be run before it tries to access
// mThread. By delaying insertion of this event into the queue, we ensure
// that mThread is set properly.
{
MutexAutoLock lock(mLock);
mEvents->PutEvent(startup);
}
// Wait for thread to call ThreadManager::SetupCurrentThread, which completes
// initialization of ThreadFunc.
startup->Wait();
return NS_OK;
}
nsresult
nsThread::InitCurrentThread()
{
mThread = PR_GetCurrentThread();
nsThreadManager::get()->RegisterCurrentThread(this);
return NS_OK;
}
nsresult
nsThread::PutEvent(nsIRunnable *event)
{
{
MutexAutoLock lock(mLock);
if (mEventsAreDoomed) {
NS_WARNING("An event was posted to a thread that will never run it (rejected)");
return NS_ERROR_UNEXPECTED;
}
if (!mEvents->PutEvent(event))
return NS_ERROR_OUT_OF_MEMORY;
}
nsCOMPtr<nsIThreadObserver> obs = GetObserver();
if (obs)
obs->OnDispatchedEvent(this);
return NS_OK;
}
//-----------------------------------------------------------------------------
// nsIEventTarget
NS_IMETHODIMP
nsThread::Dispatch(nsIRunnable *event, PRUint32 flags)
{
LOG(("THRD(%p) Dispatch [%p %x]\n", this, event, flags));
NS_ENSURE_ARG_POINTER(event);
if (flags & DISPATCH_SYNC) {
nsThread *thread = nsThreadManager::get()->GetCurrentThread();
NS_ENSURE_STATE(thread);
// XXX we should be able to do something better here... we should
// be able to monitor the slot occupied by this event and use
// that to tell us when the event has been processed.
nsRefPtr<nsThreadSyncDispatch> wrapper =
new nsThreadSyncDispatch(thread, event);
if (!wrapper)
return NS_ERROR_OUT_OF_MEMORY;
nsresult rv = PutEvent(wrapper);
// Don't wait for the event to finish if we didn't dispatch it...
if (NS_FAILED(rv))
return rv;
while (wrapper->IsPending())
NS_ProcessNextEvent(thread);
return wrapper->Result();
}
NS_ASSERTION(flags == NS_DISPATCH_NORMAL, "unexpected dispatch flags");
return PutEvent(event);
}
NS_IMETHODIMP
nsThread::IsOnCurrentThread(PRBool *result)
{
*result = (PR_GetCurrentThread() == mThread);
return NS_OK;
}
//-----------------------------------------------------------------------------
// nsIThread
NS_IMETHODIMP
nsThread::GetPRThread(PRThread **result)
{
*result = mThread;
return NS_OK;
}
NS_IMETHODIMP
nsThread::Shutdown()
{
LOG(("THRD(%p) shutdown\n", this));
// XXX If we make this warn, then we hit that warning at xpcom shutdown while
// shutting down a thread in a thread pool. That happens b/c the thread
// in the thread pool is already shutdown by the thread manager.
if (!mThread)
return NS_OK;
NS_ENSURE_STATE(mThread != PR_GetCurrentThread());
// Prevent multiple calls to this method
{
MutexAutoLock lock(mLock);
if (!mShutdownRequired)
return NS_ERROR_UNEXPECTED;
mShutdownRequired = PR_FALSE;
}
nsThreadShutdownContext context;
context.joiningThread = nsThreadManager::get()->GetCurrentThread();
context.shutdownAck = PR_FALSE;
// Set mShutdownContext and wake up the thread in case it is waiting for
// events to process.
nsCOMPtr<nsIRunnable> event = new nsThreadShutdownEvent(this, &context);
if (!event)
return NS_ERROR_OUT_OF_MEMORY;
// XXXroc What if posting the event fails due to OOM?
PutEvent(event);
// We could still end up with other events being added after the shutdown
// task, but that's okay because we process pending events in ThreadFunc
// after setting mShutdownContext just before exiting.
// Process events on the current thread until we receive a shutdown ACK.
while (!context.shutdownAck)
NS_ProcessNextEvent(context.joiningThread);
// Now, it should be safe to join without fear of dead-locking.
PR_JoinThread(mThread);
mThread = nsnull;
#ifdef DEBUG
{
MutexAutoLock lock(mLock);
NS_ASSERTION(!mObserver, "Should have been cleared at shutdown!");
}
#endif
return NS_OK;
}
NS_IMETHODIMP
nsThread::HasPendingEvents(PRBool *result)
{
NS_ENSURE_STATE(PR_GetCurrentThread() == mThread);
*result = mEvents->GetEvent(PR_FALSE, nsnull);
return NS_OK;
}
#ifdef MOZ_CANARY
void canary_alarm_handler (int signum);
class Canary {
//XXX ToDo: support nested loops
public:
Canary() {
if (sOutputFD != 0 && EventLatencyIsImportant()) {
if (sOutputFD == -1) {
const int flags = O_WRONLY | O_APPEND | O_CREAT | O_NONBLOCK;
const mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
char* env_var_flag = getenv("MOZ_KILL_CANARIES");
sOutputFD = env_var_flag ? (env_var_flag[0] ?
open(env_var_flag, flags, mode) :
STDERR_FILENO) : 0;
if (sOutputFD == 0)
return;
}
signal(SIGALRM, canary_alarm_handler);
ualarm(15000, 0);
}
}
~Canary() {
if (sOutputFD != 0 && EventLatencyIsImportant())
ualarm(0, 0);
}
static bool EventLatencyIsImportant() {
return NS_IsMainThread() && XRE_GetProcessType() == GeckoProcessType_Default;
}
static int sOutputFD;
};
int Canary::sOutputFD = -1;
void canary_alarm_handler (int signum)
{
void *array[30];
const char msg[29] = "event took too long to run:\n";
// use write to be safe in the signal handler
write(Canary::sOutputFD, msg, sizeof(msg));
backtrace_symbols_fd(array, backtrace(array, 30), Canary::sOutputFD);
}
#endif
#define NOTIFY_EVENT_OBSERVERS(func_, params_) \
PR_BEGIN_MACRO \
if (!mEventObservers.IsEmpty()) { \
nsAutoTObserverArray<nsCOMPtr<nsIThreadObserver>, 2>::ForwardIterator \
iter_(mEventObservers); \
nsCOMPtr<nsIThreadObserver> obs_; \
while (iter_.HasMore()) { \
obs_ = iter_.GetNext(); \
obs_ -> func_ params_ ; \
} \
} \
PR_END_MACRO
NS_IMETHODIMP
nsThread::ProcessNextEvent(PRBool mayWait, PRBool *result)
{
LOG(("THRD(%p) ProcessNextEvent [%u %u]\n", this, mayWait, mRunningEvent));
NS_ENSURE_STATE(PR_GetCurrentThread() == mThread);
PRBool notifyGlobalObserver = (sGlobalObserver != nsnull);
if (notifyGlobalObserver)
sGlobalObserver->OnProcessNextEvent(this, mayWait && !ShuttingDown(),
mRunningEvent);
nsCOMPtr<nsIThreadObserver> obs = mObserver;
if (obs)
obs->OnProcessNextEvent(this, mayWait && !ShuttingDown(), mRunningEvent);
NOTIFY_EVENT_OBSERVERS(OnProcessNextEvent,
(this, mayWait && !ShuttingDown(), mRunningEvent));
++mRunningEvent;
#ifdef MOZ_CANARY
Canary canary;
#endif
nsresult rv = NS_OK;
{
// Scope for |event| to make sure that its destructor fires while
// mRunningEvent has been incremented, since that destructor can
// also do work.
// If we are shutting down, then do not wait for new events.
nsCOMPtr<nsIRunnable> event;
mEvents->GetEvent(mayWait && !ShuttingDown(), getter_AddRefs(event));
#ifdef NS_FUNCTION_TIMER
char message[1024] = {'\0'};
if (NS_IsMainThread()) {
mozilla::FunctionTimer::ft_snprintf(message, sizeof(message),
"@ Main Thread Event %p", (void*)event.get());
}
// If message is empty, it means that we're not on the main thread, and
// FunctionTimer won't time this function.
NS_TIME_FUNCTION_MIN_FMT(5.0, message);
#endif
*result = (event.get() != nsnull);
if (event) {
LOG(("THRD(%p) running [%p]\n", this, event.get()));
event->Run();
} else if (mayWait) {
NS_ASSERTION(ShuttingDown(),
"This should only happen when shutting down");
rv = NS_ERROR_UNEXPECTED;
}
}
--mRunningEvent;
NOTIFY_EVENT_OBSERVERS(AfterProcessNextEvent, (this, mRunningEvent));
if (obs)
obs->AfterProcessNextEvent(this, mRunningEvent);
if (notifyGlobalObserver && sGlobalObserver)
sGlobalObserver->AfterProcessNextEvent(this, mRunningEvent);
return rv;
}
//-----------------------------------------------------------------------------
// nsISupportsPriority
NS_IMETHODIMP
nsThread::GetPriority(PRInt32 *priority)
{
*priority = mPriority;
return NS_OK;
}
NS_IMETHODIMP
nsThread::SetPriority(PRInt32 priority)
{
NS_ENSURE_STATE(mThread);
// NSPR defines the following four thread priorities:
// PR_PRIORITY_LOW
// PR_PRIORITY_NORMAL
// PR_PRIORITY_HIGH
// PR_PRIORITY_URGENT
// We map the priority values defined on nsISupportsPriority to these values.
mPriority = priority;
PRThreadPriority pri;
if (mPriority <= PRIORITY_HIGHEST) {
pri = PR_PRIORITY_URGENT;
} else if (mPriority < PRIORITY_NORMAL) {
pri = PR_PRIORITY_HIGH;
} else if (mPriority > PRIORITY_NORMAL) {
pri = PR_PRIORITY_LOW;
} else {
pri = PR_PRIORITY_NORMAL;
}
PR_SetThreadPriority(mThread, pri);
return NS_OK;
}
NS_IMETHODIMP
nsThread::AdjustPriority(PRInt32 delta)
{
return SetPriority(mPriority + delta);
}
//-----------------------------------------------------------------------------
// nsIThreadInternal
NS_IMETHODIMP
nsThread::GetObserver(nsIThreadObserver **obs)
{
MutexAutoLock lock(mLock);
NS_IF_ADDREF(*obs = mObserver);
return NS_OK;
}
NS_IMETHODIMP
nsThread::SetObserver(nsIThreadObserver *obs)
{
NS_ENSURE_STATE(PR_GetCurrentThread() == mThread);
MutexAutoLock lock(mLock);
mObserver = obs;
return NS_OK;
}
NS_IMETHODIMP
nsThread::PushEventQueue(nsIThreadEventFilter *filter)
{
nsChainedEventQueue *queue = new nsChainedEventQueue(filter);
MutexAutoLock lock(mLock);
queue->mNext = mEvents;
mEvents = queue;
return NS_OK;
}
NS_IMETHODIMP
nsThread::PopEventQueue()
{
MutexAutoLock lock(mLock);
// Make sure we do not pop too many!
NS_ENSURE_STATE(mEvents != &mEventsRoot);
nsChainedEventQueue *queue = mEvents;
mEvents = mEvents->mNext;
nsCOMPtr<nsIRunnable> event;
while (queue->GetEvent(PR_FALSE, getter_AddRefs(event)))
mEvents->PutEvent(event);
delete queue;
return NS_OK;
}
PRBool
nsThread::nsChainedEventQueue::PutEvent(nsIRunnable *event)
{
PRBool val;
if (!mFilter || mFilter->AcceptEvent(event)) {
val = mQueue.PutEvent(event);
} else {
val = mNext->PutEvent(event);
}
return val;
}
//-----------------------------------------------------------------------------
// nsIThreadInternal2
NS_IMETHODIMP
nsThread::GetRecursionDepth(PRUint32 *depth)
{
NS_ENSURE_ARG_POINTER(depth);
NS_ENSURE_STATE(PR_GetCurrentThread() == mThread);
*depth = mRunningEvent;
return NS_OK;
}
NS_IMETHODIMP
nsThread::AddObserver(nsIThreadObserver *observer)
{
NS_ENSURE_ARG_POINTER(observer);
NS_ENSURE_STATE(PR_GetCurrentThread() == mThread);
NS_WARN_IF_FALSE(!mEventObservers.Contains(observer),
"Adding an observer twice!");
if (!mEventObservers.AppendElement(observer)) {
NS_WARNING("Out of memory!");
return NS_ERROR_OUT_OF_MEMORY;
}
return NS_OK;
}
NS_IMETHODIMP
nsThread::RemoveObserver(nsIThreadObserver *observer)
{
NS_ENSURE_STATE(PR_GetCurrentThread() == mThread);
if (observer && !mEventObservers.RemoveElement(observer)) {
NS_WARNING("Removing an observer that was never added!");
}
return NS_OK;
}
//-----------------------------------------------------------------------------
NS_IMETHODIMP
nsThreadSyncDispatch::Run()
{
if (mSyncTask) {
mResult = mSyncTask->Run();
mSyncTask = nsnull;
// unblock the origin thread
mOrigin->Dispatch(this, NS_DISPATCH_NORMAL);
}
return NS_OK;
}
nsresult
NS_SetGlobalThreadObserver(nsIThreadObserver* aObserver)
{
if (aObserver && nsThread::sGlobalObserver) {
return NS_ERROR_NOT_AVAILABLE;
}
if (!NS_IsMainThread()) {
return NS_ERROR_UNEXPECTED;
}
nsThread::sGlobalObserver = aObserver;
return NS_OK;
}