Add BufferHubEventFd

The main use case of BufferHubEventFd is to signal buffer state change
cross multiple processes without explicit IPC.

Intended architecture: There will be one BufferHubEventFd per
BufferNode object and multiple clients of the same BufferNode should
share the same kernel object of the eventFd.

This CL focuses on proving eventfd and epollfd fit our needs. More
work is needed for BufferHubEventFd to make it binder-parcelable with
necessary constructors.

Bug: 68770788
Test: BufferHubBuffer_test
Change-Id: I7f7f5e5762fa81df61b649c306d209be2fd4236c

1 files changed, 47 insertions, 0 deletions

diff --git a/libs/ui/BufferHubEventFd.cpp b/libs/ui/BufferHubEventFd.cpp
new file mode 100644
index 0000000000..978b3526f3
--- /dev/null
+++ b/libs/ui/BufferHubEventFd.cpp
@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+#include <sys/eventfd.h>
+
+#include <log/log.h>
+#include <ui/BufferHubEventFd.h>
+
+namespace android {
+
+BufferHubEventFd::BufferHubEventFd() : mFd(eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK)) {}
+
+status_t BufferHubEventFd::signal() const {
+    if (!isValid()) {
+        ALOGE("%s: cannot signal an invalid eventfd.", __FUNCTION__);
+        return DEAD_OBJECT;
+    }
+
+    eventfd_write(mFd.get(), 1);
+    return OK;
+}
+
+status_t BufferHubEventFd::clear() const {
+    if (!isValid()) {
+        ALOGE("%s: cannot clear an invalid eventfd.", __FUNCTION__);
+        return DEAD_OBJECT;
+    }
+
+    eventfd_t value;
+    eventfd_read(mFd.get(), &value);
+    return OK;
+}
+
+} // namespace android