/* -*- 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");

}

#ifdef XP_DARWIN

inline 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");

}

#endif

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_);

}