Ben Murdoch | b8a8cc1 | 2014-11-26 15:28:44 +0000 | [diff] [blame] | 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 | void CallOnceImpl(OnceType* once, PointerArgFunction init_func, void* arg) { |
| 19 | AtomicWord state = Acquire_Load(once); |
| 20 | // Fast path. The provided function was already executed. |
| 21 | if (state == ONCE_STATE_DONE) { |
| 22 | 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 | if (state == ONCE_STATE_UNINITIALIZED) { |
| 35 | // We are the first thread to call this function, so we have to call the |
| 36 | // function. |
| 37 | init_func(arg); |
| 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 | while (state == ONCE_STATE_EXECUTING_FUNCTION) { |
| 43 | #ifdef _WIN32 |
| 44 | ::Sleep(0); |
| 45 | #else |
| 46 | sched_yield(); |
| 47 | #endif |
| 48 | state = Acquire_Load(once); |
| 49 | } |
| 50 | } |
| 51 | } |
| 52 | |
Ben Murdoch | 4a90d5f | 2016-03-22 12:00:34 +0000 | [diff] [blame] | 53 | } // namespace base |
| 54 | } // namespace v8 |