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Try to fix design flaw where a timer's destructor races with TimerThread::Run -- really want a better design, but this patches the problem in the context of the current design (118004, r=dbradley/pavlov, sr=shaver/jband, a=asa).

Browse Source 
git-svn-id: svn://10.0.0.236/trunk@116167 18797224-902f-48f8-a5cc-f745e15eee43
This commit is contained in:
brendan%mozilla.org
2002-03-08 20:11:49 +00:00
parent 7c143418b6
commit 3758741719
10 changed files with 171 additions and 73 deletions
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50
mozilla/xpcom/threads/TimerThread.cpp
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@@ -63,6 +63,12 @@ TimerThread::~TimerThread()
PR_DestroyLock(mLock);
mThread = nsnull;
PRInt32 n = mTimers.Count();
while (--n >= 0) {
nsTimerImpl *timer = NS_STATIC_CAST(nsTimerImpl *, mTimers[n]);
NS_RELEASE(timer);
}
}
nsresult TimerThread::Init()
@@ -189,8 +195,14 @@ NS_IMETHODIMP TimerThread::Run()
if (now >= timer->mTimeout + mTimeoutAdjustment) {
next:
RemoveTimerInternal(timer);
// NB: AddRef before the Release under RemoveTimerInternal to avoid
// mRefCnt passing through zero, in case all other refs than the one
// from mTimers have gone away (the last non-mTimers[i]-ref's Release
// must be racing with us, blocked in gThread->RemoveTimer waiting
// for TimerThread::mLock, under nsTimerImpl::Release.
NS_ADDREF(timer);
RemoveTimerInternal(timer);
// We release mLock around the Fire call, of course, to avoid deadlock.
lock.unlock();
@@ -261,6 +273,8 @@ nsresult TimerThread::AddTimer(nsTimerImpl *aTimer)
/* add the timer from our list */
PRInt32 i = AddTimerInternal(aTimer);
if (i < 0)
return NS_ERROR_OUT_OF_MEMORY;
if (mCondVar && mWaiting && i == 0)
PR_NotifyCondVar(mCondVar);
@@ -272,8 +286,12 @@ nsresult TimerThread::TimerDelayChanged(nsTimerImpl *aTimer)
{
nsAutoLock lock(mLock);
// Our caller has a strong ref to aTimer, so it can't go away here under
// ReleaseTimerInternal.
RemoveTimerInternal(aTimer);
AddTimerInternal(aTimer);
if (AddTimerInternal(aTimer) < 0)
return NS_ERROR_OUT_OF_MEMORY;
return NS_OK;
}
@@ -282,8 +300,15 @@ nsresult TimerThread::RemoveTimer(nsTimerImpl *aTimer)
{
nsAutoLock lock(mLock);
/* remove the timer from our list */
RemoveTimerInternal(aTimer);
// Remove the timer from our array. Tell callers that aTimer was not found
// by returning NS_ERROR_NOT_AVAILABLE. Unlike the TimerDelayChanged case
// immediately above, our caller may be passing a (now-)weak ref in via the
// aTimer param, specifically when nsTimerImpl::Release loses a race with
// TimerThread::Run, must wait for the mLock auto-lock here, and during the
// wait Run drops the only remaining ref to aTimer via RemoveTimerInternal.
if (!RemoveTimerInternal(aTimer))
return NS_ERROR_NOT_AVAILABLE;
return NS_OK;
}
@@ -300,7 +325,22 @@ PRInt32 TimerThread::AddTimerInternal(nsTimerImpl *aTimer)
break;
}
}
mTimers.InsertElementAt(aTimer, i);
if (!mTimers.InsertElementAt(aTimer, i))
return -1;
aTimer->mArmed = PR_TRUE;
NS_ADDREF(aTimer);
return i;
}
PRBool TimerThread::RemoveTimerInternal(nsTimerImpl *aTimer)
{
if (!mTimers.RemoveElement(aTimer))
return PR_FALSE;
// Order is crucial here -- see nsTimerImpl::Release.
aTimer->mArmed = PR_FALSE;
NS_RELEASE(aTimer);
return PR_TRUE;
}