SF: Extract utils::OnceFuture
Make `mRenderEnginePrimeCacheFuture` thread-safe and release its shared
state after the wait.
Bug: 328459745
Test: presubmit
Change-Id: I2bf3029823109a8c97e599d20c15e46ac1e4aeb9
diff --git a/services/surfaceflinger/Utils/OnceFuture.h b/services/surfaceflinger/Utils/OnceFuture.h
new file mode 100644
index 0000000..412038c
--- /dev/null
+++ b/services/surfaceflinger/Utils/OnceFuture.h
@@ -0,0 +1,53 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <future>
+#include <mutex>
+
+#include <android-base/thread_annotations.h>
+
+namespace android::utils {
+
+// Allows a thread to `wait` for a future produced by a different thread. The future is returned by
+// the first call to a function `F` that multiple threads may `callOnce`. If no `callOnce` happens,
+// then `wait` does nothing. Otherwise, it blocks on the future, then destroys it, which resets the
+// `OnceFuture`.
+class OnceFuture {
+public:
+ template <typename F>
+ void callOnce(F f) {
+ std::lock_guard lock(mMutex);
+ if (!mFuture.valid()) {
+ mFuture = f();
+ }
+ }
+
+ void wait() {
+ std::lock_guard lock(mMutex);
+ if (mFuture.valid()) {
+ mFuture.wait();
+ mFuture = {};
+ }
+ }
+
+private:
+ std::mutex mMutex;
+ std::future<void> mFuture GUARDED_BY(mMutex);
+};
+
+} // namespace android::utils