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Diffstat (limited to 'memory/build/Mutex.h')
| -rw-r--r-- | memory/build/Mutex.h | 197 |
1 files changed, 197 insertions, 0 deletions
diff --git a/memory/build/Mutex.h b/memory/build/Mutex.h new file mode 100644 index 0000000000..17ebadc0d1 --- /dev/null +++ b/memory/build/Mutex.h @@ -0,0 +1,197 @@ +/* -*- 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/. */ + +#ifndef Mutex_h +#define Mutex_h + +#if defined(XP_WIN) +# include <windows.h> +#elif defined(XP_DARWIN) +# include "mozilla/Assertions.h" +# include <os/lock.h> +#else +# include <pthread.h> +#endif +#include "mozilla/Attributes.h" +#include "mozilla/ThreadSafety.h" + +#if defined(XP_DARWIN) +// For information about the following undocumented flags and functions see +// https://github.com/apple/darwin-xnu/blob/main/bsd/sys/ulock.h and +// https://github.com/apple/darwin-libplatform/blob/main/private/os/lock_private.h +# define OS_UNFAIR_LOCK_DATA_SYNCHRONIZATION (0x00010000) +# define OS_UNFAIR_LOCK_ADAPTIVE_SPIN (0x00040000) + +extern "C" { + +typedef uint32_t os_unfair_lock_options_t; +OS_UNFAIR_LOCK_AVAILABILITY +OS_EXPORT OS_NOTHROW OS_NONNULL_ALL void os_unfair_lock_lock_with_options( + os_unfair_lock_t lock, os_unfair_lock_options_t options); +} +#endif // defined(XP_DARWIN) + +// Mutexes based on spinlocks. We can't use normal pthread spinlocks in all +// places, because they require malloc()ed memory, which causes bootstrapping +// issues in some cases. We also can't use constructors, because for statics, +// they would fire after the first use of malloc, resetting the locks. +struct MOZ_CAPABILITY("mutex") Mutex { +#if defined(XP_WIN) + CRITICAL_SECTION mMutex; +#elif defined(XP_DARWIN) + os_unfair_lock mMutex; +#else + pthread_mutex_t mMutex; +#endif + + // Initializes a mutex. Returns whether initialization succeeded. + inline bool Init() { +#if defined(XP_WIN) + if (!InitializeCriticalSectionAndSpinCount(&mMutex, 5000)) { + return false; + } +#elif defined(XP_DARWIN) + mMutex = OS_UNFAIR_LOCK_INIT; +#elif defined(XP_LINUX) && !defined(ANDROID) + pthread_mutexattr_t attr; + if (pthread_mutexattr_init(&attr) != 0) { + return false; + } + pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ADAPTIVE_NP); + if (pthread_mutex_init(&mMutex, &attr) != 0) { + pthread_mutexattr_destroy(&attr); + return false; + } + pthread_mutexattr_destroy(&attr); +#else + if (pthread_mutex_init(&mMutex, nullptr) != 0) { + return false; + } +#endif + return true; + } + + inline void Lock() MOZ_CAPABILITY_ACQUIRE() { +#if defined(XP_WIN) + EnterCriticalSection(&mMutex); +#elif defined(XP_DARWIN) + // We rely on a non-public function to improve performance here. + // The OS_UNFAIR_LOCK_DATA_SYNCHRONIZATION flag informs the kernel that + // the calling thread is able to make progress even in absence of actions + // from other threads and the OS_UNFAIR_LOCK_ADAPTIVE_SPIN one causes the + // kernel to spin on a contested lock if the owning thread is running on + // the same physical core (presumably only on x86 CPUs given that ARM + // macs don't have cores capable of SMT). On versions of macOS older than + // 10.15 the latter is not available and we spin in userspace instead. + if (Mutex::gSpinInKernelSpace) { + os_unfair_lock_lock_with_options( + &mMutex, + OS_UNFAIR_LOCK_DATA_SYNCHRONIZATION | OS_UNFAIR_LOCK_ADAPTIVE_SPIN); + } else { +# if defined(__x86_64__) + // On older versions of macOS (10.14 and older) the + // `OS_UNFAIR_LOCK_ADAPTIVE_SPIN` flag is not supported by the kernel, + // we spin in user-space instead like `OSSpinLock` does: + // https://github.com/apple/darwin-libplatform/blob/215b09856ab5765b7462a91be7076183076600df/src/os/lock.c#L183-L198 + // Note that `OSSpinLock` uses 1000 iterations on x86-64: + // https://github.com/apple/darwin-libplatform/blob/215b09856ab5765b7462a91be7076183076600df/src/os/lock.c#L93 + // ...but we only use 100 like it does on ARM: + // https://github.com/apple/darwin-libplatform/blob/215b09856ab5765b7462a91be7076183076600df/src/os/lock.c#L90 + // We choose this value because it yields the same results in our + // benchmarks but is less likely to have detrimental effects caused by + // excessive spinning. + uint32_t retries = 100; + + do { + if (os_unfair_lock_trylock(&mMutex)) { + return; + } + + __asm__ __volatile__("pause"); + } while (retries--); + + os_unfair_lock_lock_with_options(&mMutex, + OS_UNFAIR_LOCK_DATA_SYNCHRONIZATION); +# else + MOZ_CRASH("User-space spin-locks should never be used on ARM"); +# endif // defined(__x86_64__) + } +#else + pthread_mutex_lock(&mMutex); +#endif + } + + inline void Unlock() MOZ_CAPABILITY_RELEASE() { +#if defined(XP_WIN) + LeaveCriticalSection(&mMutex); +#elif defined(XP_DARWIN) + os_unfair_lock_unlock(&mMutex); +#else + pthread_mutex_unlock(&mMutex); +#endif + } + +#if defined(XP_DARWIN) + static bool SpinInKernelSpace(); + static const bool gSpinInKernelSpace; +#endif // XP_DARWIN +}; + +// Mutex that can be used for static initialization. +// On Windows, CRITICAL_SECTION requires a function call to be initialized, +// but for the initialization lock, a static initializer calling the +// function would be called too late. We need no-function-call +// initialization, which SRWLock provides. +// Ideally, we'd use the same type of locks everywhere, but SRWLocks +// everywhere incur a performance penalty. See bug 1418389. +#if defined(XP_WIN) +struct MOZ_CAPABILITY("mutex") StaticMutex { + SRWLOCK mMutex; + + inline void Lock() MOZ_CAPABILITY_ACQUIRE() { + AcquireSRWLockExclusive(&mMutex); + } + + inline void Unlock() MOZ_CAPABILITY_RELEASE() { + ReleaseSRWLockExclusive(&mMutex); + } +}; + +// Normally, we'd use a constexpr constructor, but MSVC likes to create +// static initializers anyways. +# define STATIC_MUTEX_INIT SRWLOCK_INIT + +#else +typedef Mutex StaticMutex; + +# if defined(XP_DARWIN) +# define STATIC_MUTEX_INIT OS_UNFAIR_LOCK_INIT +# elif defined(XP_LINUX) && !defined(ANDROID) +# define STATIC_MUTEX_INIT PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP +# else +# define STATIC_MUTEX_INIT PTHREAD_MUTEX_INITIALIZER +# endif + +#endif + +template <typename T> +struct MOZ_SCOPED_CAPABILITY MOZ_RAII AutoLock { + explicit AutoLock(T& aMutex) MOZ_CAPABILITY_ACQUIRE(aMutex) : mMutex(aMutex) { + mMutex.Lock(); + } + + ~AutoLock() MOZ_CAPABILITY_RELEASE() { mMutex.Unlock(); } + + AutoLock(const AutoLock&) = delete; + AutoLock(AutoLock&&) = delete; + + private: + T& mMutex; +}; + +using MutexAutoLock = AutoLock<Mutex>; + +#endif |