SkOnce: add option to call another cleanup function once at exit.

include/core/SkOnce.h

 /*
  * 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 "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);
+inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)() = NULL);
 
 //  ----------------------  Implementation details below here. -----------------------------
 
 struct SkOnceFlag {
     bool done;
     SkSpinlock lock;
 };
 
 // TODO(bungeman, mtklein): move all these *barrier* functions to SkThread when refactoring lands.
 
@@ skipping 36 matching lines @@
 }
 
 // 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 Func, typename Arg>
-static void sk_once_slow(SkOnceFlag* once, Func f, Arg arg) {
+static void sk_once_slow(SkOnceFlag* once, Func f, Arg arg, void (*atExit)()) {
     const SkAutoSpinlock lock(&once->lock);
     if (!once->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();
@@ skipping 11 matching lines @@
 extern "C" {
 void AnnotateBenignRace(const char* file, int line, const volatile void* mem, const char* desc);
 }
 #define SK_ANNOTATE_BENIGN_RACE(mem, desc) AnnotateBenignRace(__FILE__, __LINE__, mem, desc)
 #else
 #define SK_ANNOTATE_BENIGN_RACE(mem, desc)
 #endif
 
 // This is our fast path, called all the time.  We do really want it to be inlined.
 template <typename Func, typename Arg>
-inline void SkOnce(SkOnceFlag* once, Func f, Arg arg) {
+inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)()) {
     SK_ANNOTATE_BENIGN_RACE(&(once->done), "Don't worry TSAN, we're sure this is safe.");
     if (!once->done) {
-        sk_once_slow(once, f, arg);
+        sk_once_slow(once, 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();
 }
 
 #undef SK_ANNOTATE_BENIGN_RACE
 
 #endif  // SkOnce_DEFINED