| // Copyright 2012 the V8 project authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "src/base/once.h" |
| |
| #ifdef _WIN32 |
| #include <windows.h> |
| #else |
| #include <sched.h> |
| #endif |
| |
| #include "src/base/atomicops.h" |
| |
| namespace v8 { |
| namespace base { |
| |
| void CallOnceImpl(OnceType* once, PointerArgFunction init_func, void* arg) { |
| AtomicWord state = Acquire_Load(once); |
| // Fast path. The provided function was already executed. |
| if (state == ONCE_STATE_DONE) { |
| return; |
| } |
| |
| // The function execution did not complete yet. The once object can be in one |
| // of the two following states: |
| // - UNINITIALIZED: We are the first thread calling this function. |
| // - EXECUTING_FUNCTION: Another thread is already executing the function. |
| // |
| // First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION |
| // atomically. |
| state = Acquire_CompareAndSwap( |
| once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_FUNCTION); |
| if (state == ONCE_STATE_UNINITIALIZED) { |
| // We are the first thread to call this function, so we have to call the |
| // function. |
| init_func(arg); |
| Release_Store(once, ONCE_STATE_DONE); |
| } else { |
| // Another thread has already started executing the function. We need to |
| // wait until it completes the initialization. |
| while (state == ONCE_STATE_EXECUTING_FUNCTION) { |
| #ifdef _WIN32 |
| ::Sleep(0); |
| #else |
| sched_yield(); |
| #endif |
| state = Acquire_Load(once); |
| } |
| } |
| } |
| |
| } // namespace base |
| } // namespace v8 |