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1//===-- mutex.h -------------------------------------------------*- C++ -*-===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef SCUDO_MUTEX_H_10#define SCUDO_MUTEX_H_11 12#include "atomic_helpers.h"13#include "common.h"14#include "thread_annotations.h"15 16#include <string.h>17 18#if SCUDO_FUCHSIA19#include <lib/sync/mutex.h> // for sync_mutex_t20#endif21 22namespace scudo {23 24class CAPABILITY("mutex") HybridMutex {25public:26 bool tryLock() TRY_ACQUIRE(true);27 NOINLINE void lock() ACQUIRE() {28 if (LIKELY(tryLock()))29 return;30 // The compiler may try to fully unroll the loop, ending up in a31 // NumberOfTries*NumberOfYields block of pauses mixed with tryLocks. This32 // is large, ugly and unneeded, a compact loop is better for our purpose33 // here. Use a pragma to tell the compiler not to unroll the loop.34#ifdef __clang__35#pragma nounroll36#endif37 for (u8 I = 0U; I < NumberOfTries; I++) {38 delayLoop();39 if (tryLock())40 return;41 }42 lockSlow();43 }44 void unlock() RELEASE();45 46 // TODO(chiahungduan): In general, we may want to assert the owner of lock as47 // well. Given the current uses of HybridMutex, it's acceptable without48 // asserting the owner. Re-evaluate this when we have certain scenarios which49 // requires a more fine-grained lock granularity.50 ALWAYS_INLINE void assertHeld() ASSERT_CAPABILITY(this) {51 if (SCUDO_DEBUG)52 assertHeldImpl();53 }54 55private:56 void delayLoop() {57 // The value comes from the average time spent in accessing caches (which58 // are the fastest operations) so that we are unlikely to wait too long for59 // fast operations.60 constexpr u32 SpinTimes = 16;61 volatile u32 V = 0;62 for (u32 I = 0; I < SpinTimes; ++I) {63 u32 Tmp = V + 1;64 V = Tmp;65 }66 }67 68 void assertHeldImpl();69 70 // TODO(chiahungduan): Adapt this value based on scenarios. E.g., primary and71 // secondary allocator have different allocation times.72 static constexpr u8 NumberOfTries = 32U;73 74#if SCUDO_LINUX75 atomic_u32 M = {};76#elif SCUDO_FUCHSIA77 sync_mutex_t M = {};78#endif79 80 void lockSlow() ACQUIRE();81};82 83class SCOPED_CAPABILITY ScopedLock {84public:85 explicit ScopedLock(HybridMutex &M) ACQUIRE(M) : Mutex(M) { Mutex.lock(); }86 ~ScopedLock() RELEASE() { Mutex.unlock(); }87 88private:89 HybridMutex &Mutex;90 91 ScopedLock(const ScopedLock &) = delete;92 void operator=(const ScopedLock &) = delete;93};94 95} // namespace scudo96 97#endif // SCUDO_MUTEX_H_98