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//===-- mutex.h -------------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef SCUDO_MUTEX_H_
#define SCUDO_MUTEX_H_
#include "atomic_helpers.h"
#include "common.h"
#include "thread_annotations.h"
#include <string.h>
#if SCUDO_FUCHSIA
#error #include <lib/sync/mutex.h> // for sync_mutex_t
#endif
namespace scudo {
class CAPABILITY("mutex") HybridMutex {
public:
bool tryLock() TRY_ACQUIRE(true);
NOINLINE void lock() ACQUIRE() {
if (LIKELY(tryLock()))
return;
// The compiler may try to fully unroll the loop, ending up in a
// NumberOfTries*NumberOfYields block of pauses mixed with tryLocks. This
// is large, ugly and unneeded, a compact loop is better for our purpose
// here. Use a pragma to tell the compiler not to unroll the loop.
#ifdef __clang__
#pragma nounroll
#endif
for (u8 I = 0U; I < NumberOfTries; I++) {
delayLoop();
if (tryLock())
return;
}
lockSlow();
}
void unlock() RELEASE();
// TODO(chiahungduan): In general, we may want to assert the owner of lock as
// well. Given the current uses of HybridMutex, it's acceptable without
// asserting the owner. Re-evaluate this when we have certain scenarios which
// requires a more fine-grained lock granularity.
ALWAYS_INLINE void assertHeld() ASSERT_CAPABILITY(this) {
if (SCUDO_DEBUG)
assertHeldImpl();
}
private:
void delayLoop() {
// The value comes from the average time spent in accessing caches (which
// are the fastest operations) so that we are unlikely to wait too long for
// fast operations.
constexpr u32 SpinTimes = 16;
volatile u32 V = 0;
for (u32 I = 0; I < SpinTimes; ++I) {
u32 Tmp = V + 1;
V = Tmp;
}
}
void assertHeldImpl();
// TODO(chiahungduan): Adapt this value based on scenarios. E.g., primary and
// secondary allocator have different allocation times.
static constexpr u8 NumberOfTries = 32U;
#if SCUDO_LINUX
atomic_u32 M = {};
#elif SCUDO_FUCHSIA
sync_mutex_t M = {};
#endif
void lockSlow() ACQUIRE();
};
class SCOPED_CAPABILITY ScopedLock {
public:
explicit ScopedLock(HybridMutex &M) ACQUIRE(M) : Mutex(M) { Mutex.lock(); }
~ScopedLock() RELEASE() { Mutex.unlock(); }
private:
HybridMutex &Mutex;
ScopedLock(const ScopedLock &) = delete;
void operator=(const ScopedLock &) = delete;
};
} // namespace scudo
#endif // SCUDO_MUTEX_H_
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