SkExecutor

Refactoring to refamiliarize myself with SkTaskGroup and SkThreadPool.

This adds an SkExecutor interface to describe how we use SkThreadPool,
with a global setter and getter for a default instance.  Then I rewrote
SkTaskGroup to work with any executor, the global default by default.

I also think I've made the SkTaskGroup::wait() borrow logic clearer
with the addition of SkSemaphore::try_wait().  This lets me keep the
semaphore count and actual count of work in perfect sync.

Change-Id: I6bbdfaeb0e2c3a43daff6192d34bc4a3f7210178
Reviewed-on: https://skia-review.googlesource.com/8836
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/include/core/SkExecutor.h b/include/core/SkExecutor.h
new file mode 100644
index 0000000000..303f9e3f54
--- /dev/null
+++ b/include/core/SkExecutor.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkExecutor_DEFINED
+#define SkExecutor_DEFINED
+
+#include <functional>
+#include <memory>
+
+class SkExecutor {
+public:
+    virtual ~SkExecutor();
+
+    // Create a thread pool SkExecutor with a fixed thread count, by default the number of cores.
+    static std::unique_ptr<SkExecutor> MakeThreadPool(int threads = 0);
+
+    // There is always a default SkExecutor available by calling SkExecutor::GetDefault().
+    static SkExecutor& GetDefault();
+    static void SetDefault(SkExecutor*);  // Does not take ownership.  Not thread safe.
+
+    // Add work to execute.
+    virtual void add(std::function<void(void)>) = 0;
+
+    // If it makes sense for this executor, use this thread to execute work for a little while.
+    virtual void borrow() {}
+};
+
+#endif//SkExecutor_DEFINED