The Tor Browser: security/sandbox/chromium/base/atomic_ref

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revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

     1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.

     2 // Use of this source code is governed by a BSD-style license that can be

     3 // found in the LICENSE file.

     5 // This is a low level implementation of atomic semantics for reference

     6 // counting.  Please use base/memory/ref_counted.h directly instead.

     7 //

     8 // The implementation includes annotations to avoid some false positives

     9 // when using data race detection tools.

    11 #ifndef BASE_ATOMIC_REF_COUNT_H_

    12 #define BASE_ATOMIC_REF_COUNT_H_

    14 #include "base/atomicops.h"

    15 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"

    17 namespace base {

    19 typedef subtle::Atomic32 AtomicRefCount;

    21 // Increment a reference count by "increment", which must exceed 0.

    22 inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr,

    23                                AtomicRefCount increment) {

    24   subtle::NoBarrier_AtomicIncrement(ptr, increment);

    25 }

    27 // Decrement a reference count by "decrement", which must exceed 0,

    28 // and return whether the result is non-zero.

    29 // Insert barriers to ensure that state written before the reference count

    30 // became zero will be visible to a thread that has just made the count zero.

    31 inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr,

    32                                AtomicRefCount decrement) {

    33   ANNOTATE_HAPPENS_BEFORE(ptr);

    34   bool res = (subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0);

    35   if (!res) {

    36     ANNOTATE_HAPPENS_AFTER(ptr);

    37   }

    38   return res;

    39 }

    41 // Increment a reference count by 1.

    42 inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) {

    43   base::AtomicRefCountIncN(ptr, 1);

    44 }

    46 // Decrement a reference count by 1 and return whether the result is non-zero.

    47 // Insert barriers to ensure that state written before the reference count

    48 // became zero will be visible to a thread that has just made the count zero.

    49 inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) {

    50   return base::AtomicRefCountDecN(ptr, 1);

    51 }

    53 // Return whether the reference count is one.  If the reference count is used

    54 // in the conventional way, a refrerence count of 1 implies that the current

    55 // thread owns the reference and no other thread shares it.  This call performs

    56 // the test for a reference count of one, and performs the memory barrier

    57 // needed for the owning thread to act on the object, knowing that it has

    58 // exclusive access to the object.

    59 inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) {

    60   bool res = (subtle::Acquire_Load(ptr) == 1);

    61   if (res) {

    62     ANNOTATE_HAPPENS_AFTER(ptr);

    63   }

    64   return res;

    65 }

    67 // Return whether the reference count is zero.  With conventional object

    68 // referencing counting, the object will be destroyed, so the reference count

    69 // should never be zero.  Hence this is generally used for a debug check.

    70 inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) {

    71   bool res = (subtle::Acquire_Load(ptr) == 0);

    72   if (res) {

    73     ANNOTATE_HAPPENS_AFTER(ptr);

    74   }

    75   return res;

    76 }

    78 }  // namespace base

    80 #endif  // BASE_ATOMIC_REF_COUNT_H_

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