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