The Tor Browser: gfx/skia/trunk/include/core/SkOnce.h@129ffea94266 (annotated)

gfx/skia/trunk/include/core/SkOnce.h@129ffea94266 (annotated)

gfx/skia/trunk/include/core/SkOnce.h

Sat, 03 Jan 2015 20:18:00 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Sat, 03 Jan 2015 20:18:00 +0100
branch: TOR_BUG_3246
changeset 7: 129ffea94266
permissions: -rw-r--r--

Conditionally enable double key logic according to:
private browsing mode or privacy.thirdparty.isolate preference and
implement in GetCookieStringCommon and FindCookie where it counts...
With some reservations of how to convince FindCookie users to test
condition and pass a nullptr when disabling double key logic.

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkOnce_DEFINED
 #define SkOnce_DEFINED
 // SkOnce.h defines SK_DECLARE_STATIC_ONCE and SkOnce(), which you can use
 // together to create a threadsafe way to call a function just once.  This
 // is particularly useful for lazy singleton initialization. E.g.
 //
 // static void set_up_my_singleton(Singleton** singleton) {
 //     *singleton = new Singleton(...);
 // }
 // ...
 // const Singleton& GetSingleton() {
 //     static Singleton* singleton = NULL;
 //     SK_DECLARE_STATIC_ONCE(once);
 //     SkOnce(&once, set_up_my_singleton, &singleton);
 //     SkASSERT(NULL != singleton);
 //     return *singleton;
 // }
 //
 // OnceTest.cpp also should serve as a few other simple examples.
 //
 // You may optionally pass SkOnce a second function to be called at exit for cleanup.
 #include "SkDynamicAnnotations.h"
 #include "SkThread.h"
 #include "SkTypes.h"
 #define SK_ONCE_INIT { false, { 0, SkDEBUGCODE(0) } }
 #define SK_DECLARE_STATIC_ONCE(name) static SkOnceFlag name = SK_ONCE_INIT
 struct SkOnceFlag;  // If manually created, initialize with SkOnceFlag once = SK_ONCE_INIT
 template <typename Func, typename Arg>
 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)() = NULL);
 // If you've already got a lock and a flag to use, this variant lets you avoid an extra SkOnceFlag.
 template <typename Lock, typename Func, typename Arg>
 inline void SkOnce(bool* done, Lock* lock, Func f, Arg arg, void(*atExit)() = NULL);
 //  ----------------------  Implementation details below here. -----------------------------
 // This is POD and must be zero-initialized.
 struct SkSpinlock {
     void acquire() {
         SkASSERT(shouldBeZero == 0);
         // No memory barrier needed, but sk_atomic_cas gives us at least release anyway.
         while (!sk_atomic_cas(&thisIsPrivate, 0, 1)) {
             // spin
         }
     }
     void release() {
         SkASSERT(shouldBeZero == 0);
         // This requires a release memory barrier before storing, which sk_atomic_cas guarantees.
         SkAssertResult(sk_atomic_cas(&thisIsPrivate, 1, 0));
     }
     int32_t thisIsPrivate;
     SkDEBUGCODE(int32_t shouldBeZero;)
 };
 struct SkOnceFlag {
     bool done;
     SkSpinlock lock;
 };
 // TODO(bungeman, mtklein): move all these *barrier* functions to SkThread when refactoring lands.
 #ifdef SK_BUILD_FOR_WIN
 #  include <intrin.h>
 inline static void compiler_barrier() {
     _ReadWriteBarrier();
 }
 #else
 inline static void compiler_barrier() {
     asm volatile("" : : : "memory");
 }
 #endif
 inline static void full_barrier_on_arm() {
 #ifdef SK_CPU_ARM
 #  if SK_ARM_ARCH >= 7
     asm volatile("dmb" : : : "memory");
 #  else
     asm volatile("mcr p15, 0, %0, c7, c10, 5" : : "r" (0) : "memory");
 #  endif
 #endif
 }
 // On every platform, we issue a compiler barrier to prevent it from reordering
 // code.  That's enough for platforms like x86 where release and acquire
 // barriers are no-ops.  On other platforms we may need to be more careful;
 // ARM, in particular, needs real code for both acquire and release.  We use a
 // full barrier, which acts as both, because that the finest precision ARM
 // provides.
 inline static void release_barrier() {
     compiler_barrier();
     full_barrier_on_arm();
 }
 inline static void acquire_barrier() {
     compiler_barrier();
     full_barrier_on_arm();
 }
 // Works with SkSpinlock or SkMutex.
 template <typename Lock>
 class SkAutoLockAcquire {
 public:
     explicit SkAutoLockAcquire(Lock* lock) : fLock(lock) { fLock->acquire(); }
     ~SkAutoLockAcquire() { fLock->release(); }
 private:
     Lock* fLock;
 };
 // We've pulled a pretty standard double-checked locking implementation apart
 // into its main fast path and a slow path that's called when we suspect the
 // one-time code hasn't run yet.
 // This is the guts of the code, called when we suspect the one-time code hasn't been run yet.
 // This should be rarely called, so we separate it from SkOnce and don't mark it as inline.
 // (We don't mind if this is an actual function call, but odds are it'll be inlined anyway.)
 template <typename Lock, typename Func, typename Arg>
 static void sk_once_slow(bool* done, Lock* lock, Func f, Arg arg, void (*atExit)()) {
     const SkAutoLockAcquire<Lock> locked(lock);
     if (!*done) {
         f(arg);
         if (atExit != NULL) {
             atexit(atExit);
         }
         // Also known as a store-store/load-store barrier, this makes sure that the writes
         // done before here---in particular, those done by calling f(arg)---are observable
         // before the writes after the line, *done = true.
         //
         // In version control terms this is like saying, "check in the work up
         // to and including f(arg), then check in *done=true as a subsequent change".
         //
         // We'll use this in the fast path to make sure f(arg)'s effects are
         // observable whenever we observe *done == true.
         release_barrier();
         *done = true;
     }
 }
 // This is our fast path, called all the time.  We do really want it to be inlined.
 template <typename Lock, typename Func, typename Arg>
 inline void SkOnce(bool* done, Lock* lock, Func f, Arg arg, void(*atExit)()) {
     if (!SK_ANNOTATE_UNPROTECTED_READ(*done)) {
         sk_once_slow(done, lock, f, arg, atExit);
     }
     // Also known as a load-load/load-store barrier, this acquire barrier makes
     // sure that anything we read from memory---in particular, memory written by
     // calling f(arg)---is at least as current as the value we read from once->done.
     //
     // In version control terms, this is a lot like saying "sync up to the
     // commit where we wrote once->done = true".
     //
     // The release barrier in sk_once_slow guaranteed that once->done = true
     // happens after f(arg), so by syncing to once->done = true here we're
     // forcing ourselves to also wait until the effects of f(arg) are readble.
     acquire_barrier();
 }
 template <typename Func, typename Arg>
 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)()) {
     return SkOnce(&once->done, &once->lock, f, arg, atExit);
 }
 #undef SK_ANNOTATE_BENIGN_RACE
 #endif  // SkOnce_DEFINED

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gfx/skia/trunk/include/core/SkOnce.h@129ffea94266 (annotated)

gfx/skia/trunk/include/core/SkOnce.h