Line data    Source code

       1             : // Copyright 2012 the V8 project 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.
       4             : 
       5             : #include "src/base/once.h"
       6             : 
       7             : #ifdef _WIN32
       8             : #include <windows.h>
       9             : #else
      10             : #include <sched.h>
      11             : #endif
      12             : 
      13             : namespace v8 {
      14             : namespace base {
      15             : 
      16      538107 : void CallOnceImpl(OnceType* once, std::function<void()> init_func) {
      17             :   // Fast path. The provided function was already executed.
      18      538107 :   if (once->load(std::memory_order_acquire) == ONCE_STATE_DONE) {
      19           0 :     return;
      20             :   }
      21             : 
      22             :   // The function execution did not complete yet. The once object can be in one
      23             :   // of the two following states:
      24             :   //   - UNINITIALIZED: We are the first thread calling this function.
      25             :   //   - EXECUTING_FUNCTION: Another thread is already executing the function.
      26             :   //
      27             :   // First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION
      28             :   // atomically.
      29      538107 :   uint8_t expected = ONCE_STATE_UNINITIALIZED;
      30      538107 :   if (once->compare_exchange_strong(expected, ONCE_STATE_EXECUTING_FUNCTION,
      31             :                                     std::memory_order_acq_rel)) {
      32             :     // We are the first thread to call this function, so we have to call the
      33             :     // function.
      34             :     init_func();
      35             :     once->store(ONCE_STATE_DONE, std::memory_order_release);
      36             :   } else {
      37             :     // Another thread has already started executing the function. We need to
      38             :     // wait until it completes the initialization.
      39       39826 :     while (once->load(std::memory_order_acquire) ==
      40             :            ONCE_STATE_EXECUTING_FUNCTION) {
      41             : #ifdef _WIN32
      42             :       ::Sleep(0);
      43             : #else
      44       19864 :       sched_yield();
      45             : #endif
      46             :     }
      47             :   }
      48             : }
      49             : 
      50             : }  // namespace base
      51             : }  // namespace v8