compiler-rt/lib/scudo/standalone/mutex.h

   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-exception
   6 //
   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_FUCHSIA
  19 #include <lib/sync/mutex.h> // for sync_mutex_t
  20 #endif
  21
  22 namespace scudo {
  23
  24 class CAPABILITY("mutex") HybridMutex {
  25 public:
  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 a
  31       // NumberOfTries*NumberOfYields block of pauses mixed with tryLocks. This
  32       // is large, ugly and unneeded, a compact loop is better for our purpose
  33       // here. Use a pragma to tell the compiler not to unroll the loop.
  34 #ifdef __clang__
  35 #pragma nounroll
  36 #endif
  37     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 as
  47   // well. Given the current uses of HybridMutex, it's acceptable without
  48   // asserting the owner. Re-evaluate this when we have certain scenarios which
  49   // requires a more fine-grained lock granularity.
  50   ALWAYS_INLINE void assertHeld() ASSERT_CAPABILITY(this) {
  51     if (SCUDO_DEBUG)
  52       assertHeldImpl();
  53   }
  54
  55 private:
  56   void delayLoop() {
  57     // The value comes from the average time spent in accessing caches (which
  58     // are the fastest operations) so that we are unlikely to wait too long for
  59     // 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 and
  71   // secondary allocator have different allocation times.
  72   static constexpr u8 NumberOfTries = 32U;
  73
  74 #if SCUDO_LINUX
  75   atomic_u32 M = {};
  76 #elif SCUDO_FUCHSIA
  77   sync_mutex_t M = {};
  78 #endif
  79
  80   void lockSlow() ACQUIRE();
  81 };
  82
  83 class SCOPED_CAPABILITY ScopedLock {
  84 public:
  85   explicit ScopedLock(HybridMutex &M) ACQUIRE(M) : Mutex(M) { Mutex.lock(); }
  86   ~ScopedLock() RELEASE() { Mutex.unlock(); }
  87
  88 private:
  89   HybridMutex &Mutex;
  90
  91   ScopedLock(const ScopedLock &) = delete;
  92   void operator=(const ScopedLock &) = delete;
  93 };
  94
  95 } // namespace scudo
  96
  97 #endif // SCUDO_MUTEX_H_