Add CallOnce() and simple LazyInstance implementation.

src/once.cc

+// Copyright 2012 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "once.h"
+
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <sched.h>
+#endif
+
+#include "atomicops.h"
+#include "checks.h"
+
+namespace v8 {
+namespace internal {
+
+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 v8::internal