third_party/tcmalloc/chromium/src/base/spinlock.h

   1 /* Copyright (c) 2006, Google Inc.
   2  * All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met:
   7  *
   8  *     * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *     * Redistributions in binary form must reproduce the above
  11  * copyright notice, this list of conditions and the following disclaimer
  12  * in the documentation and/or other materials provided with the
  13  * distribution.
  14  *     * Neither the name of Google Inc. nor the names of its
  15  * contributors may be used to endorse or promote products derived from
  16  * this software without specific prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  19  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  21  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  22  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  23  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  24  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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  28  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  29  *
  30  * ---
  31  * Author: Sanjay Ghemawat
  32  */
  33
  34 //
  35 // Fast spinlocks (at least on x86, a lock/unlock pair is approximately
  36 // half the cost of a Mutex because the unlock just does a store instead
  37 // of a compare-and-swap which is expensive).
  38
  39 // SpinLock is async signal safe.
  40 // If used within a signal handler, all lock holders
  41 // should block the signal even outside the signal handler.
  42
  43 #ifndef BASE_SPINLOCK_H_
  44 #define BASE_SPINLOCK_H_
  45
  46 #include <config.h>
  47 #include "base/atomicops.h"
  48 #include "base/basictypes.h"
  49 #include "base/dynamic_annotations.h"
  50 #include "base/thread_annotations.h"
  51
  52 class LOCKABLE SpinLock {
  53  public:
  54   SpinLock() : lockword_(kSpinLockFree) { }
  55
  56   // Special constructor for use with static SpinLock objects.  E.g.,
  57   //
  58   //    static SpinLock lock(base::LINKER_INITIALIZED);
  59   //
  60   // When intialized using this constructor, we depend on the fact
  61   // that the linker has already initialized the memory appropriately.
  62   // A SpinLock constructed like this can be freely used from global
  63   // initializers without worrying about the order in which global
  64   // initializers run.
  65   explicit SpinLock(base::LinkerInitialized /*x*/) {
  66     // Does nothing; lockword_ is already initialized
  67   }
  68
  69   // Acquire this SpinLock.
  70   // TODO(csilvers): uncomment the annotation when we figure out how to
  71   //                 support this macro with 0 args (see thread_annotations.h)
  72   inline void Lock() /*EXCLUSIVE_LOCK_FUNCTION()*/ {
  73     if (base::subtle::Acquire_CompareAndSwap(&lockword_, kSpinLockFree,
  74                                              kSpinLockHeld) != kSpinLockFree) {
  75       SlowLock();
  76     }
  77     ANNOTATE_RWLOCK_ACQUIRED(this, 1);
  78   }
  79
  80   // Try to acquire this SpinLock without blocking and return true if the
  81   // acquisition was successful.  If the lock was not acquired, false is
  82   // returned.  If this SpinLock is free at the time of the call, TryLock
  83   // will return true with high probability.
  84   inline bool TryLock() EXCLUSIVE_TRYLOCK_FUNCTION(true) {
  85     bool res =
  86         (base::subtle::Acquire_CompareAndSwap(&lockword_, kSpinLockFree,
  87                                               kSpinLockHeld) == kSpinLockFree);
  88     if (res) {
  89       ANNOTATE_RWLOCK_ACQUIRED(this, 1);
  90     }
  91     return res;
  92   }
  93
  94   // Release this SpinLock, which must be held by the calling thread.
  95   // TODO(csilvers): uncomment the annotation when we figure out how to
  96   //                 support this macro with 0 args (see thread_annotations.h)
  97   inline void Unlock() /*UNLOCK_FUNCTION()*/ {
  98     uint64 wait_cycles =
  99         static_cast<uint64>(base::subtle::NoBarrier_Load(&lockword_));
 100     ANNOTATE_RWLOCK_RELEASED(this, 1);
 101     base::subtle::Release_Store(&lockword_, kSpinLockFree);
 102     if (wait_cycles != kSpinLockHeld) {
 103       // Collect contentionz profile info, and speed the wakeup of any waiter.
 104       // The wait_cycles value indicates how long this thread spent waiting
 105       // for the lock.
 106       SlowUnlock(wait_cycles);
 107     }
 108   }
 109
 110   // Determine if the lock is held.  When the lock is held by the invoking
 111   // thread, true will always be returned. Intended to be used as
 112   // CHECK(lock.IsHeld()).
 113   inline bool IsHeld() const {
 114     return base::subtle::NoBarrier_Load(&lockword_) != kSpinLockFree;
 115   }
 116
 117   static const base::LinkerInitialized LINKER_INITIALIZED;  // backwards compat
 118  private:
 119   enum { kSpinLockFree = 0 };
 120   enum { kSpinLockHeld = 1 };
 121   enum { kSpinLockSleeper = 2 };
 122
 123   volatile Atomic32 lockword_;
 124
 125   void SlowLock();
 126   void SlowUnlock(uint64 wait_cycles);
 127   Atomic32 SpinLoop(int64 initial_wait_timestamp, Atomic32* wait_cycles);
 128   inline int32 CalculateWaitCycles(int64 wait_start_time);
 129
 130   DISALLOW_COPY_AND_ASSIGN(SpinLock);
 131 };
 132
 133 // Corresponding locker object that arranges to acquire a spinlock for
 134 // the duration of a C++ scope.
 135 class SCOPED_LOCKABLE SpinLockHolder {
 136  private:
 137   SpinLock* lock_;
 138  public:
 139   inline explicit SpinLockHolder(SpinLock* l) EXCLUSIVE_LOCK_FUNCTION(l)
 140       : lock_(l) {
 141     l->Lock();
 142   }
 143   // TODO(csilvers): uncomment the annotation when we figure out how to
 144   //                 support this macro with 0 args (see thread_annotations.h)
 145   inline ~SpinLockHolder() /*UNLOCK_FUNCTION()*/ { lock_->Unlock(); }
 146 };
 147 // Catch bug where variable name is omitted, e.g. SpinLockHolder (&lock);
 148 #define SpinLockHolder(x) COMPILE_ASSERT(0, spin_lock_decl_missing_var_name)
 149
 150
 151 #endif  // BASE_SPINLOCK_H_