skia WIPjarred/canvas

1 files changed, 53 insertions, 0 deletions

diff --git a/src/deps/skia/include/private/SkOnce.h b/src/deps/skia/include/private/SkOnce.h
new file mode 100644
index 000000000..edf3e8335
--- /dev/null
+++ b/src/deps/skia/include/private/SkOnce.h
@@ -0,0 +1,53 @@
+/*
+ * 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
+
+#include "include/private/SkThreadAnnotations.h"
+#include <atomic>
+#include <utility>
+
+// SkOnce provides call-once guarantees for Skia, much like std::once_flag/std::call_once().
+//
+// There should be no particularly error-prone gotcha use cases when using SkOnce.
+// It works correctly as a class member, a local, a global, a function-scoped static, whatever.
+
+class SkOnce {
+public:
+    constexpr SkOnce() = default;
+
+    template <typename Fn, typename... Args>
+    void operator()(Fn&& fn, Args&&... args) {
+        auto state = fState.load(std::memory_order_acquire);
+
+        if (state == Done) {
+            return;
+        }
+
+        // If it looks like no one has started calling fn(), try to claim that job.
+        if (state == NotStarted && fState.compare_exchange_strong(state, Claimed,
+                                                                  std::memory_order_relaxed,
+                                                                  std::memory_order_relaxed)) {
+            // Great!  We'll run fn() then notify the other threads by releasing Done into fState.
+            fn(std::forward<Args>(args)...);
+            return fState.store(Done, std::memory_order_release);
+        }
+
+        // Some other thread is calling fn().
+        // We'll just spin here acquiring until it releases Done into fState.
+        SK_POTENTIALLY_BLOCKING_REGION_BEGIN;
+        while (fState.load(std::memory_order_acquire) != Done) { /*spin*/ }
+        SK_POTENTIALLY_BLOCKING_REGION_END;
+    }
+
+private:
+    enum State : uint8_t { NotStarted, Claimed, Done};
+    std::atomic<uint8_t> fState{NotStarted};
+};
+
+#endif  // SkOnce_DEFINED