1    :  // Copyright 2016 Google Inc. All Rights Reserved.
   2    :  //
   3    :  // Licensed under the Apache License, Version 2.0 (the "License");
   4    :  // you may not use this file except in compliance with the License.
   5    :  // You may obtain a copy of the License at
   6    :  //
   7    :  //     http://www.apache.org/licenses/LICENSE-2.0
   8    :  //
   9    :  // Unless required by applicable law or agreed to in writing, software
  10    :  // distributed under the License is distributed on an "AS IS" BASIS,
  11    :  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12    :  // See the License for the specific language governing permissions and
  13    :  // limitations under the License.
  14    :  
  15    :  #include "syzygy/agent/asan/heap_managers/deferred_free_thread.h"
  16    :  
  17    :  namespace agent {
  18    :  namespace asan {
  19    :  namespace heap_managers {
  20    :  
  21    :  DeferredFreeThread::DeferredFreeThread(Callback deferred_free_callback)
  22  E :      : deferred_free_callback_(deferred_free_callback),
  23  E :        deferred_free_event_(false, false),
  24  E :        deferred_free_signaled_(0),
  25  E :        ready_event_(false, false),
  26  E :        enabled_(0) {
  27  E :  }
  28    :  
  29  E :  DeferredFreeThread::~DeferredFreeThread() {
  30  E :    DCHECK_EQ(0, base::subtle::NoBarrier_Load(&enabled_));
  31  E :  }
  32    :  
  33  E :  bool DeferredFreeThread::Start() {
  34  E :    auto old_enabled = base::subtle::NoBarrier_AtomicExchange(&enabled_, 1);
  35  E :    DCHECK_EQ(0, old_enabled);
  36    :    // Make sure the change to |enabled_| is not reordered.
  37  E :    base::subtle::MemoryBarrier();
  38  E :    if (!base::PlatformThread::CreateWithPriority(
  39    :            0, this, &deferred_free_thread_handle_,
  40    :            base::ThreadPriority::BACKGROUND)) {
  41  i :      return false;
  42    :    }
  43  E :    ready_event_.Wait();
  44  E :    return true;
  45  E :  }
  46    :  
  47  E :  void DeferredFreeThread::Stop() {
  48  E :    auto old_enabled = base::subtle::NoBarrier_AtomicExchange(&enabled_, 0);
  49  E :    DCHECK_EQ(1, old_enabled);
  50    :    // Make sure the change to |enabled_| is not reordered.
  51  E :    base::subtle::MemoryBarrier();
  52    :    // Signal so that the thread can exit cleanly and then join it.
  53  E :    deferred_free_event_.Signal();
  54  E :    base::PlatformThread::Join(deferred_free_thread_handle_);
  55  E :  }
  56    :  
  57  E :  void DeferredFreeThread::SignalWork() {
  58    :    // Avoid over signaling by trying to raise the |deferred_free_signaled_| flag
  59    :    // and bailing if the flag was already raised.
  60    :    auto initial_deferred_free_signaled =
  61  E :        base::subtle::NoBarrier_CompareAndSwap(&deferred_free_signaled_, 0, 1);
  62  E :    if (initial_deferred_free_signaled)
  63  i :      return;
  64    :  
  65  E :    deferred_free_event_.Signal();
  66  E :  }
  67    :  
  68  E :  void DeferredFreeThread::ThreadMain() {
  69  E :    base::PlatformThread::SetName("SyzyASAN Deferred Free Thread");
  70  E :    deferred_free_thread_id_ = base::PlatformThread::CurrentId();
  71  E :    ready_event_.Signal();
  72  E :    while (true) {
  73  E :      deferred_free_event_.Wait();
  74  E :      if (!base::subtle::NoBarrier_Load(&enabled_))
  75  E :        break;
  76    :      // Clear the |deferred_free_signaled_| flag before executing the callback.
  77    :      auto initial_deferred_free_signaled =
  78  E :          base::subtle::NoBarrier_CompareAndSwap(&deferred_free_signaled_, 1, 0);
  79  E :      DCHECK(initial_deferred_free_signaled);
  80  E :      deferred_free_callback_.Run();
  81  E :    }
  82  E :  }
  83    :  
  84    :  }  // namespace heap_managers
  85    :  }  // namespace asan
  86    :  }  // namespace agent