gecko/xpcom/threads/TimerThread.cpp
2012-07-30 17:20:58 +03:00

495 lines
14 KiB
C++

/* -*- 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 "nsTimerImpl.h"
#include "TimerThread.h"
#include "nsThreadUtils.h"
#include "pratom.h"
#include "nsIObserverService.h"
#include "nsIServiceManager.h"
#include "mozilla/Services.h"
#include <math.h>
using namespace mozilla;
NS_IMPL_THREADSAFE_ISUPPORTS2(TimerThread, nsIRunnable, nsIObserver)
TimerThread::TimerThread() :
mInitInProgress(0),
mInitialized(false),
mMonitor("TimerThread.mMonitor"),
mShutdown(false),
mWaiting(false),
mSleeping(false),
mDelayLineCounter(0),
mMinTimerPeriod(0)
{
}
TimerThread::~TimerThread()
{
mThread = nullptr;
NS_ASSERTION(mTimers.IsEmpty(), "Timers remain in TimerThread::~TimerThread");
}
nsresult
TimerThread::InitLocks()
{
return NS_OK;
}
namespace {
class TimerObserverRunnable : public nsRunnable
{
public:
TimerObserverRunnable(nsIObserver* observer)
: mObserver(observer)
{ }
NS_DECL_NSIRUNNABLE
private:
nsCOMPtr<nsIObserver> mObserver;
};
NS_IMETHODIMP
TimerObserverRunnable::Run()
{
nsCOMPtr<nsIObserverService> observerService =
mozilla::services::GetObserverService();
if (observerService) {
observerService->AddObserver(mObserver, "sleep_notification", false);
observerService->AddObserver(mObserver, "wake_notification", false);
}
return NS_OK;
}
} // anonymous namespace
nsresult TimerThread::Init()
{
PR_LOG(gTimerLog, PR_LOG_DEBUG, ("TimerThread::Init [%d]\n", mInitialized));
if (mInitialized) {
if (!mThread)
return NS_ERROR_FAILURE;
return NS_OK;
}
if (PR_ATOMIC_SET(&mInitInProgress, 1) == 0) {
// We hold on to mThread to keep the thread alive.
nsresult rv = NS_NewThread(getter_AddRefs(mThread), this);
if (NS_FAILED(rv)) {
mThread = nullptr;
}
else {
nsRefPtr<TimerObserverRunnable> r = new TimerObserverRunnable(this);
if (NS_IsMainThread()) {
r->Run();
}
else {
NS_DispatchToMainThread(r);
}
}
{
MonitorAutoLock lock(mMonitor);
mInitialized = true;
mMonitor.NotifyAll();
}
}
else {
MonitorAutoLock lock(mMonitor);
while (!mInitialized) {
mMonitor.Wait();
}
}
if (!mThread)
return NS_ERROR_FAILURE;
return NS_OK;
}
nsresult TimerThread::Shutdown()
{
PR_LOG(gTimerLog, PR_LOG_DEBUG, ("TimerThread::Shutdown begin\n"));
if (!mThread)
return NS_ERROR_NOT_INITIALIZED;
nsTArray<nsTimerImpl*> timers;
{ // lock scope
MonitorAutoLock lock(mMonitor);
mShutdown = true;
// notify the cond var so that Run() can return
if (mWaiting)
mMonitor.Notify();
// Need to copy content of mTimers array to a local array
// because call to timers' ReleaseCallback() (and release its self)
// must not be done under the lock. Destructor of a callback
// might potentially call some code reentering the same lock
// that leads to unexpected behavior or deadlock.
// See bug 422472.
timers.AppendElements(mTimers);
mTimers.Clear();
}
PRUint32 timersCount = timers.Length();
for (PRUint32 i = 0; i < timersCount; i++) {
nsTimerImpl *timer = timers[i];
timer->ReleaseCallback();
ReleaseTimerInternal(timer);
}
mThread->Shutdown(); // wait for the thread to die
PR_LOG(gTimerLog, PR_LOG_DEBUG, ("TimerThread::Shutdown end\n"));
return NS_OK;
}
// Keep track of how early (positive slack) or late (negative slack) timers
// are running, and use the filtered slack number to adaptively estimate how
// early timers should fire to be "on time".
void TimerThread::UpdateFilter(PRUint32 aDelay, TimeStamp aTimeout,
TimeStamp aNow)
{
TimeDuration slack = aTimeout - aNow;
double smoothSlack = 0;
PRUint32 i, filterLength;
static TimeDuration kFilterFeedbackMaxTicks =
TimeDuration::FromMilliseconds(FILTER_FEEDBACK_MAX);
static TimeDuration kFilterFeedbackMinTicks =
TimeDuration::FromMilliseconds(-FILTER_FEEDBACK_MAX);
if (slack > kFilterFeedbackMaxTicks)
slack = kFilterFeedbackMaxTicks;
else if (slack < kFilterFeedbackMinTicks)
slack = kFilterFeedbackMinTicks;
mDelayLine[mDelayLineCounter & DELAY_LINE_LENGTH_MASK] =
slack.ToMilliseconds();
if (++mDelayLineCounter < DELAY_LINE_LENGTH) {
// Startup mode: accumulate a full delay line before filtering.
PR_ASSERT(mTimeoutAdjustment.ToSeconds() == 0);
filterLength = 0;
} else {
// Past startup: compute number of filter taps based on mMinTimerPeriod.
if (mMinTimerPeriod == 0) {
mMinTimerPeriod = (aDelay != 0) ? aDelay : 1;
} else if (aDelay != 0 && aDelay < mMinTimerPeriod) {
mMinTimerPeriod = aDelay;
}
filterLength = (PRUint32) (FILTER_DURATION / mMinTimerPeriod);
if (filterLength > DELAY_LINE_LENGTH)
filterLength = DELAY_LINE_LENGTH;
else if (filterLength < 4)
filterLength = 4;
for (i = 1; i <= filterLength; i++)
smoothSlack += mDelayLine[(mDelayLineCounter-i) & DELAY_LINE_LENGTH_MASK];
smoothSlack /= filterLength;
// XXXbe do we need amplification? hacking a fudge factor, need testing...
mTimeoutAdjustment = TimeDuration::FromMilliseconds(smoothSlack * 1.5);
}
#ifdef DEBUG_TIMERS
PR_LOG(gTimerLog, PR_LOG_DEBUG,
("UpdateFilter: smoothSlack = %g, filterLength = %u\n",
smoothSlack, filterLength));
#endif
}
/* void Run(); */
NS_IMETHODIMP TimerThread::Run()
{
PR_SetCurrentThreadName("Timer");
MonitorAutoLock lock(mMonitor);
// We need to know how many microseconds give a positive PRIntervalTime. This
// is platform-dependent, we calculate it at runtime now.
// First we find a value such that PR_MicrosecondsToInterval(high) = 1
PRInt32 low = 0, high = 1;
while (PR_MicrosecondsToInterval(high) == 0)
high <<= 1;
// We now have
// PR_MicrosecondsToInterval(low) = 0
// PR_MicrosecondsToInterval(high) = 1
// and we can proceed to find the critical value using binary search
while (high-low > 1) {
PRInt32 mid = (high+low) >> 1;
if (PR_MicrosecondsToInterval(mid) == 0)
low = mid;
else
high = mid;
}
// Half of the amount of microseconds needed to get positive PRIntervalTime.
// We use this to decide how to round our wait times later
PRInt32 halfMicrosecondsIntervalResolution = high >> 1;
while (!mShutdown) {
// Have to use PRIntervalTime here, since PR_WaitCondVar takes it
PRIntervalTime waitFor;
if (mSleeping) {
// Sleep for 0.1 seconds while not firing timers.
waitFor = PR_MillisecondsToInterval(100);
} else {
waitFor = PR_INTERVAL_NO_TIMEOUT;
TimeStamp now = TimeStamp::Now();
nsTimerImpl *timer = nullptr;
if (!mTimers.IsEmpty()) {
timer = mTimers[0];
if (now >= timer->mTimeout + mTimeoutAdjustment) {
next:
// 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::mMonitor, under nsTimerImpl::Release.
NS_ADDREF(timer);
RemoveTimerInternal(timer);
{
// We release mMonitor around the Fire call to avoid deadlock.
MonitorAutoUnlock unlock(mMonitor);
#ifdef DEBUG_TIMERS
if (PR_LOG_TEST(gTimerLog, PR_LOG_DEBUG)) {
PR_LOG(gTimerLog, PR_LOG_DEBUG,
("Timer thread woke up %fms from when it was supposed to\n",
fabs((now - timer->mTimeout).ToMilliseconds())));
}
#endif
// We are going to let the call to PostTimerEvent here handle the
// release of the timer so that we don't end up releasing the timer
// on the TimerThread instead of on the thread it targets.
if (NS_FAILED(timer->PostTimerEvent())) {
nsrefcnt rc;
NS_RELEASE2(timer, rc);
// The nsITimer interface requires that its users keep a reference
// to the timers they use while those timers are initialized but
// have not yet fired. If this ever happens, it is a bug in the
// code that created and used the timer.
//
// Further, note that this should never happen even with a
// misbehaving user, because nsTimerImpl::Release checks for a
// refcount of 1 with an armed timer (a timer whose only reference
// is from the timer thread) and when it hits this will remove the
// timer from the timer thread and thus destroy the last reference,
// preventing this situation from occurring.
NS_ASSERTION(rc != 0, "destroyed timer off its target thread!");
}
timer = nullptr;
}
if (mShutdown)
break;
// Update now, as PostTimerEvent plus the locking may have taken a
// tick or two, and we may goto next below.
now = TimeStamp::Now();
}
}
if (!mTimers.IsEmpty()) {
timer = mTimers[0];
TimeStamp timeout = timer->mTimeout + mTimeoutAdjustment;
// Don't wait at all (even for PR_INTERVAL_NO_WAIT) if the next timer
// is due now or overdue.
//
// Note that we can only sleep for integer values of a certain
// resolution. We use halfMicrosecondsIntervalResolution, calculated
// before, to do the optimal rounding (i.e., of how to decide what
// interval is so small we should not wait at all).
double microseconds = (timeout - now).ToMilliseconds()*1000;
if (microseconds < halfMicrosecondsIntervalResolution)
goto next; // round down; execute event now
waitFor = PR_MicrosecondsToInterval(microseconds);
if (waitFor == 0)
waitFor = 1; // round up, wait the minimum time we can wait
}
#ifdef DEBUG_TIMERS
if (PR_LOG_TEST(gTimerLog, PR_LOG_DEBUG)) {
if (waitFor == PR_INTERVAL_NO_TIMEOUT)
PR_LOG(gTimerLog, PR_LOG_DEBUG,
("waiting for PR_INTERVAL_NO_TIMEOUT\n"));
else
PR_LOG(gTimerLog, PR_LOG_DEBUG,
("waiting for %u\n", PR_IntervalToMilliseconds(waitFor)));
}
#endif
}
mWaiting = true;
mMonitor.Wait(waitFor);
mWaiting = false;
}
return NS_OK;
}
nsresult TimerThread::AddTimer(nsTimerImpl *aTimer)
{
MonitorAutoLock lock(mMonitor);
// Add the timer to our list.
PRInt32 i = AddTimerInternal(aTimer);
if (i < 0)
return NS_ERROR_OUT_OF_MEMORY;
// Awaken the timer thread.
if (mWaiting && i == 0)
mMonitor.Notify();
return NS_OK;
}
nsresult TimerThread::TimerDelayChanged(nsTimerImpl *aTimer)
{
MonitorAutoLock lock(mMonitor);
// Our caller has a strong ref to aTimer, so it can't go away here under
// ReleaseTimerInternal.
RemoveTimerInternal(aTimer);
PRInt32 i = AddTimerInternal(aTimer);
if (i < 0)
return NS_ERROR_OUT_OF_MEMORY;
// Awaken the timer thread.
if (mWaiting && i == 0)
mMonitor.Notify();
return NS_OK;
}
nsresult TimerThread::RemoveTimer(nsTimerImpl *aTimer)
{
MonitorAutoLock lock(mMonitor);
// 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 mMonitor 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;
// Awaken the timer thread.
if (mWaiting)
mMonitor.Notify();
return NS_OK;
}
// This function must be called from within a lock
PRInt32 TimerThread::AddTimerInternal(nsTimerImpl *aTimer)
{
if (mShutdown)
return -1;
TimeStamp now = TimeStamp::Now();
PRUint32 count = mTimers.Length();
PRUint32 i = 0;
for (; i < count; i++) {
nsTimerImpl *timer = mTimers[i];
// Don't break till we have skipped any overdue timers.
// XXXbz why? Given our definition of overdue in terms of
// mTimeoutAdjustment, aTimer might be overdue already! Why not
// just fire timers in order?
// XXX does this hold for TYPE_REPEATING_PRECISE? /be
if (now < timer->mTimeout + mTimeoutAdjustment &&
aTimer->mTimeout < timer->mTimeout) {
break;
}
}
if (!mTimers.InsertElementAt(i, aTimer))
return -1;
aTimer->mArmed = true;
NS_ADDREF(aTimer);
return i;
}
bool TimerThread::RemoveTimerInternal(nsTimerImpl *aTimer)
{
if (!mTimers.RemoveElement(aTimer))
return false;
ReleaseTimerInternal(aTimer);
return true;
}
void TimerThread::ReleaseTimerInternal(nsTimerImpl *aTimer)
{
// Order is crucial here -- see nsTimerImpl::Release.
aTimer->mArmed = false;
NS_RELEASE(aTimer);
}
void TimerThread::DoBeforeSleep()
{
mSleeping = true;
}
void TimerThread::DoAfterSleep()
{
mSleeping = true; // wake may be notified without preceding sleep notification
for (PRUint32 i = 0; i < mTimers.Length(); i ++) {
nsTimerImpl *timer = mTimers[i];
// get and set the delay to cause its timeout to be recomputed
PRUint32 delay;
timer->GetDelay(&delay);
timer->SetDelay(delay);
}
// nuke the stored adjustments, so they get recalibrated
mTimeoutAdjustment = TimeDuration(0);
mDelayLineCounter = 0;
mSleeping = false;
}
/* void observe (in nsISupports aSubject, in string aTopic, in wstring aData); */
NS_IMETHODIMP
TimerThread::Observe(nsISupports* /* aSubject */, const char *aTopic, const PRUnichar* /* aData */)
{
if (strcmp(aTopic, "sleep_notification") == 0)
DoBeforeSleep();
else if (strcmp(aTopic, "wake_notification") == 0)
DoAfterSleep();
return NS_OK;
}