[core] Introduce the util::Alarm

A variation of util::Timer that does not require owning thread
to sleep in a select().

3 files changed, 100 insertions, 0 deletions

diff --git a/cmake/core-files.cmake b/cmake/core-files.cmake
index 1bbe739256..0d27c81aee 100644
--- a/cmake/core-files.cmake
+++ b/cmake/core-files.cmake
@@ -563,6 +563,8 @@ set(MBGL_CORE_FILES
     include/mbgl/util/work_request.hpp
     include/mbgl/util/work_task.hpp
     include/mbgl/util/work_task_impl.hpp
+    src/mbgl/util/alarm.cpp
+    src/mbgl/util/alarm.hpp
     src/mbgl/util/chrono.cpp
     src/mbgl/util/clip_id.cpp
     src/mbgl/util/clip_id.hpp
diff --git a/src/mbgl/util/alarm.cpp b/src/mbgl/util/alarm.cpp
new file mode 100644
index 0000000000..1d20321db9
--- /dev/null
+++ b/src/mbgl/util/alarm.cpp
@@ -0,0 +1,58 @@
+#include <mbgl/util/alarm.hpp>
+
+#include <mbgl/actor/actor_ref.hpp>
+#include <mbgl/actor/mailbox.hpp>
+#include <mbgl/util/run_loop.hpp>
+#include <mbgl/util/timer.hpp>
+
+#include <cassert>
+
+namespace mbgl {
+namespace util {
+
+class Alarm::Impl {
+public:
+    Impl(ActorRef<Alarm::Impl>, ActorRef<Alarm> parent_) : parent(parent_) {}
+
+    void start(Duration timeout) {
+        alarm.start(timeout, mbgl::Duration::zero(), [this]() {
+            parent.invoke(&Alarm::fired);
+        });
+    }
+
+    void stop() {
+        alarm.stop();
+    }
+
+private:
+    Timer alarm;
+    ActorRef<Alarm> parent;
+};
+
+Alarm::Alarm()
+    // FIXME: Replace with util::Scheduler::Get()
+    : mailbox(std::make_shared<Mailbox>(*util::RunLoop::Get()))
+    , impl("Alarm", ActorRef<Alarm>(*this, mailbox)) {
+}
+
+Alarm::~Alarm() {
+    mailbox->close();
+}
+
+void Alarm::start(Duration timeout, std::function<void()>&& cb) {
+    assert(cb);
+    callback = std::move(cb);
+
+    impl.actor().invoke(&Impl::start, timeout);
+}
+
+void Alarm::stop() {
+    impl.actor().invoke(&Impl::stop);
+}
+
+void Alarm::fired() {
+    callback();
+}
+
+} // namespace util
+} // namespace mbgl
diff --git a/src/mbgl/util/alarm.hpp b/src/mbgl/util/alarm.hpp
new file mode 100644
index 0000000000..81e92d74c7
--- /dev/null
+++ b/src/mbgl/util/alarm.hpp
@@ -0,0 +1,40 @@
+#pragma once
+
+#include <mbgl/util/chrono.hpp>
+#include <mbgl/util/noncopyable.hpp>
+#include <mbgl/util/thread.hpp>
+
+#include <functional>
+#include <memory>
+
+namespace mbgl {
+
+class Mailbox;
+
+namespace util {
+
+// Alarm works similarly to the util::Timer class, with the
+// difference it does not require the owning thread to sleep
+// in a select(). It is useful for platforms like Android
+// where you cannot set a timer on the main thread because the
+// NDK does not have a concept of timeout callback in the ALooper.
+class Alarm : private util::noncopyable {
+public:
+    Alarm();
+    ~Alarm();
+
+    void start(Duration timeout, std::function<void()>&&);
+    void stop();
+
+private:
+    class Impl;
+
+    void fired();
+
+    std::shared_ptr<Mailbox> mailbox;
+    util::Thread<Impl> impl;
+    std::function<void()> callback;
+};
+
+} // namespace util
+} // namespace mbgl