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             : #include "src/base/atomicops.h"
      14             : 
      15             : namespace v8 {
      16             : namespace base {
      17             : 
      18      525194 : void CallOnceImpl(OnceType* once, std::function<void()> init_func) {
      19             :   AtomicWord state = Acquire_Load(once);
      20             :   // Fast path. The provided function was already executed.
      21      525194 :   if (state == ONCE_STATE_DONE) {
      22      525194 :     return;
      23             :   }
      24             : 
      25             :   // The function execution did not complete yet. The once object can be in one
      26             :   // of the two following states:
      27             :   //   - UNINITIALIZED: We are the first thread calling this function.
      28             :   //   - EXECUTING_FUNCTION: Another thread is already executing the function.
      29             :   //
      30             :   // First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION
      31             :   // atomically.
      32             :   state = Acquire_CompareAndSwap(
      33             :       once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_FUNCTION);
      34      525264 :   if (state == ONCE_STATE_UNINITIALIZED) {
      35             :     // We are the first thread to call this function, so we have to call the
      36             :     // function.
      37      524707 :     init_func();
      38             :     Release_Store(once, ONCE_STATE_DONE);
      39             :   } else {
      40             :     // Another thread has already started executing the function. We need to
      41             :     // wait until it completes the initialization.
      42      348694 :     while (state == ONCE_STATE_EXECUTING_FUNCTION) {
      43             : #ifdef _WIN32
      44             :       ::Sleep(0);
      45             : #else
      46      348137 :       sched_yield();
      47             : #endif
      48             :       state = Acquire_Load(once);
      49             :     }
      50             :   }
      51             : }
      52             : 
      53             : }  // namespace base
      54             : }  // namespace v8