[libcamera-devel] [PATCH v9 2/4] cam: event_loop: Add timer events to event loop

[Eric Curtin]

Extend the EventLoop class to support periodic timer events. This can be
used to run tasks periodically, such as handling the event loop of SDL.

Also delete all events in the list, before we event_base_loopbreak, in
an effort to avoid race conditions.

Signed-off-by: Eric Curtin <ecurtin at redhat.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
Tested-by: Jacopo Mondi <jacopo at jmondi.org>
---
 src/cam/event_loop.cpp | 27 +++++++++++++++++++++++++++
 src/cam/event_loop.h   |  7 ++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/cam/event_loop.cpp b/src/cam/event_loop.cpp
index 2e3ce995..315da38a 100644
--- a/src/cam/event_loop.cpp
+++ b/src/cam/event_loop.cpp
@@ -47,6 +47,8 @@ int EventLoop::exec()
 void EventLoop::exit(int code)
 {
 	exitCode_ = code;
+	events_.clear();
+
 	event_base_loopbreak(base_);
 }
 
@@ -84,6 +86,31 @@ void EventLoop::addFdEvent(int fd, EventType type,
 	events_.push_back(std::move(event));
 }
 
+void EventLoop::addTimerEvent(const duration period,
+			      const std::function<void()> &callback)
+{
+	std::unique_ptr<Event> event = std::make_unique<Event>(callback);
+	event->event_ = event_new(base_, -1, EV_PERSIST, &EventLoop::Event::dispatch,
+				  event.get());
+	if (!event->event_) {
+		std::cerr << "Failed to create timer event" << std::endl;
+		return;
+	}
+
+	struct timeval tv;
+	const uint64_t usecs = std::chrono::duration_cast<std::chrono::microseconds>(period).count();
+	tv.tv_sec = usecs / 1000000ULL;
+	tv.tv_usec = usecs % 1000000ULL;
+
+	const int ret = event_add(event->event_, &tv);
+	if (ret < 0) {
+		std::cerr << "Failed to add timer event" << std::endl;
+		return;
+	}
+
+	events_.push_back(std::move(event));
+}
+
 void EventLoop::dispatchCallback([[maybe_unused]] evutil_socket_t fd,
 				 [[maybe_unused]] short flags, void *param)
 {
diff --git a/src/cam/event_loop.h b/src/cam/event_loop.h
index 79902d87..22769ea5 100644
--- a/src/cam/event_loop.h
+++ b/src/cam/event_loop.h
@@ -7,9 +7,10 @@
 
 #pragma once
 
+#include <chrono>
 #include <functional>
-#include <memory>
 #include <list>
+#include <memory>
 #include <mutex>
 
 #include <event2/util.h>
@@ -37,6 +38,10 @@ public:
 	void addFdEvent(int fd, EventType type,
 			const std::function<void()> &handler);
 
+	using duration = std::chrono::steady_clock::duration;
+	void addTimerEvent(const duration period,
+			   const std::function<void()> &handler);
+
 private:
 	struct Event {
 		Event(const std::function<void()> &callback);
-- 
2.35.3