mozglue/misc/Mutex_posix.cpp
author Gerald Squelart <gsquelart@mozilla.com>
Thu, 04 Jul 2019 04:38:16 +0000
changeset 481213 8fed7bc35767fdfab4bac0908ae9b21c08f49e1f
parent 454520 5f4630838d46dd81dadb13220a4af0da9e23a619
child 515833 d407a28318e68dd78af8365a1ea3f8f7384f92c5
permissions -rw-r--r--
Bug 1559000 - mozglue's AutoProfilerLabel doesn't need to know about ProfilingStack - r=mstange `ProfilingStack*` happens to be the information that the current Gecko Profiler entry function wants to forward to the exit function, but AutoProfilerLabel does not really need to know about that. Changing it to `void*`, so that we can later use different entry/exit functions that use different context types. Differential Revision: https://phabricator.services.mozilla.com/D34806

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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 "mozilla/Assertions.h"
#include "mozilla/Maybe.h"

#include <algorithm>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <unistd.h>

#include "mozilla/PlatformMutex.h"
#include "MutexPlatformData_posix.h"

#define REPORT_PTHREADS_ERROR(result, msg) \
  {                                        \
    errno = result;                        \
    perror(msg);                           \
    MOZ_CRASH(msg);                        \
  }

#define TRY_CALL_PTHREADS(call, msg)      \
  {                                       \
    int result = (call);                  \
    if (result != 0) {                    \
      REPORT_PTHREADS_ERROR(result, msg); \
    }                                     \
  }

#ifdef XP_DARWIN

// CPU count. Read concurrently from multiple threads. Written once during the
// first mutex initialization; re-initialization is safe hence relaxed ordering
// is OK.
static mozilla::Atomic<uint32_t, mozilla::MemoryOrdering::Relaxed,
                       mozilla::recordreplay::Behavior::DontPreserve>
    sCPUCount(0);

static void EnsureCPUCount() {
  if (sCPUCount) {
    return;
  }

  // _SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN are common, but not
  // standard.
#  if defined(_SC_NPROCESSORS_CONF)
  long n = sysconf(_SC_NPROCESSORS_CONF);
  sCPUCount = (n > 0) ? uint32_t(n) : 1;
#  elif defined(_SC_NPROCESSORS_ONLN)
  long n = sysconf(_SC_NPROCESSORS_ONLN);
  sCPUCount = (n > 0) ? uint32_t(n) : 1;
#  else
  sCPUCount = 1;
#  endif
}

#endif  // XP_DARWIN

mozilla::detail::MutexImpl::MutexImpl(recordreplay::Behavior aRecorded)
#ifdef XP_DARWIN
    : averageSpins(0)
#endif
{
  pthread_mutexattr_t* attrp = nullptr;

  mozilla::Maybe<mozilla::recordreplay::AutoEnsurePassThroughThreadEvents> pt;
  if (aRecorded == recordreplay::Behavior::DontPreserve) {
    pt.emplace();
  }

  // Linux with glibc and FreeBSD support adaptive mutexes that spin
  // for a short number of tries before sleeping.  NSPR's locks did
  // this, too, and it seems like a reasonable thing to do.
#if (defined(__linux__) && defined(__GLIBC__)) || defined(__FreeBSD__)
#  define ADAPTIVE_MUTEX_SUPPORTED
#endif

#if defined(DEBUG)
#  define ATTR_REQUIRED
#  define MUTEX_KIND PTHREAD_MUTEX_ERRORCHECK
#elif defined(ADAPTIVE_MUTEX_SUPPORTED)
#  define ATTR_REQUIRED
#  define MUTEX_KIND PTHREAD_MUTEX_ADAPTIVE_NP
#endif

#if defined(ATTR_REQUIRED)
  pthread_mutexattr_t attr;

  TRY_CALL_PTHREADS(
      pthread_mutexattr_init(&attr),
      "mozilla::detail::MutexImpl::MutexImpl: pthread_mutexattr_init failed");

  TRY_CALL_PTHREADS(pthread_mutexattr_settype(&attr, MUTEX_KIND),
                    "mozilla::detail::MutexImpl::MutexImpl: "
                    "pthread_mutexattr_settype failed");
  attrp = &attr;
#endif

  TRY_CALL_PTHREADS(
      pthread_mutex_init(&platformData()->ptMutex, attrp),
      "mozilla::detail::MutexImpl::MutexImpl: pthread_mutex_init failed");

#if defined(ATTR_REQUIRED)
  TRY_CALL_PTHREADS(pthread_mutexattr_destroy(&attr),
                    "mozilla::detail::MutexImpl::MutexImpl: "
                    "pthread_mutexattr_destroy failed");
#endif

#ifdef XP_DARWIN
  EnsureCPUCount();
#endif
}

mozilla::detail::MutexImpl::~MutexImpl() {
  TRY_CALL_PTHREADS(
      pthread_mutex_destroy(&platformData()->ptMutex),
      "mozilla::detail::MutexImpl::~MutexImpl: pthread_mutex_destroy failed");
}

inline void mozilla::detail::MutexImpl::mutexLock() {
  TRY_CALL_PTHREADS(
      pthread_mutex_lock(&platformData()->ptMutex),
      "mozilla::detail::MutexImpl::mutexLock: pthread_mutex_lock failed");
}

bool mozilla::detail::MutexImpl::tryLock() { return mutexTryLock(); }

bool mozilla::detail::MutexImpl::mutexTryLock() {
  int result = pthread_mutex_trylock(&platformData()->ptMutex);
  if (result == 0) {
    return true;
  }

  if (result == EBUSY) {
    return false;
  }

  REPORT_PTHREADS_ERROR(
      result,
      "mozilla::detail::MutexImpl::mutexTryLock: pthread_mutex_trylock failed");
}

void mozilla::detail::MutexImpl::lock() {
#ifndef XP_DARWIN
  mutexLock();
#else
  // Mutex performance on OSX can be very poor if there's a lot of contention as
  // this causes excessive context switching. On Linux/FreeBSD we use the
  // adaptive mutex type (PTHREAD_MUTEX_ADAPTIVE_NP) to address this, but this
  // isn't available on OSX. The code below is a reimplementation of this
  // feature.

  MOZ_ASSERT(sCPUCount);
  if (sCPUCount == 1 || recordreplay::IsRecordingOrReplaying()) {
    mutexLock();
    return;
  }

  if (!mutexTryLock()) {
    const int32_t SpinLimit = 100;

    int32_t count = 0;
    int32_t maxSpins = std::min(SpinLimit, 2 * averageSpins + 10);
    do {
      if (count >= maxSpins) {
        mutexLock();
        break;
      }
      asm("pause");  // Hint to the processor that we're spinning.
      count++;
    } while (!mutexTryLock());

    // Update moving average.
    averageSpins += (count - averageSpins) / 8;
    MOZ_ASSERT(averageSpins >= 0 && averageSpins <= SpinLimit);
  }
#endif  // XP_DARWIN
}

void mozilla::detail::MutexImpl::unlock() {
  TRY_CALL_PTHREADS(
      pthread_mutex_unlock(&platformData()->ptMutex),
      "mozilla::detail::MutexImpl::unlock: pthread_mutex_unlock failed");
}

#undef TRY_CALL_PTHREADS

mozilla::detail::MutexImpl::PlatformData*
mozilla::detail::MutexImpl::platformData() {
  static_assert(sizeof(platformData_) >= sizeof(PlatformData),
                "platformData_ is too small");
  return reinterpret_cast<PlatformData*>(platformData_);
}