phosphor-fan: Create timer class

This class can be used to call an arbitrary function
after a certain amount of time, which is set in
microseconds.

Change-Id: Ifd65bbf0c3482db4e37efc3b1ccc868e62fa0afa
Signed-off-by: Matt Spinler <spinler@us.ibm.com>

1 files changed, 178 insertions, 0 deletions

diff --git a/timer.hpp b/timer.hpp
new file mode 100644
index 0000000..ea28176
--- /dev/null
+++ b/timer.hpp
@@ -0,0 +1,178 @@
+#pragma once
+
+#include <chrono>
+#include <functional>
+#include <memory>
+#include <systemd/sd-event.h>
+
+namespace phosphor
+{
+namespace fan
+{
+namespace util
+{
+
+struct EventSourceDeleter
+{
+    void operator()(sd_event_source* eventSource) const
+    {
+        sd_event_source_unref(eventSource);
+    }
+};
+
+using EventSourcePtr = std::unique_ptr<sd_event_source, EventSourceDeleter>;
+
+using EventPtr = std::shared_ptr<sd_event>;
+
+/**
+ * @class Timer
+ *
+ * This class implements a simple timer that runs an arbitrary
+ * function on expiration.  The timeout value is set in microseconds.
+ * It can be stopped while it is running, and queried to see if it is
+ * running.
+ *
+ * If started with the 'repeating' argument, it will keep calling the
+ * callback function every <timeout> microseconds.  If started with the
+ * 'oneshot' argument, it will just call the callback function one time.
+ *
+ * It needs an sd_event loop to function.
+ */
+class Timer
+{
+    public:
+
+        enum class TimerType
+        {
+            oneshot,
+            repeating
+        };
+
+        Timer() = delete;
+        Timer(const Timer&) = delete;
+        Timer& operator=(const Timer&) = delete;
+        Timer(Timer&&) = default;
+        Timer& operator=(Timer&&) = default;
+
+        /**
+         * @brief Constructs timer object
+         *
+         * @param[in] events - sd_event pointer, previously created
+         * @param[in] callbackFunc - The function to call on timer expiration
+         */
+        Timer(EventPtr& events,
+              std::function<void()> callbackFunc);
+
+        /**
+         * @brief Destructor
+         */
+        ~Timer();
+
+        /**
+         * @brief Starts the timer
+         *
+         * The input is an offset from the current steady clock.
+         *
+         * @param[in] usec - the timeout value in microseconds
+         * @param[in] type - either a oneshot, or repeating
+         */
+        void start(std::chrono::microseconds usec,
+                   TimerType type = TimerType::oneshot);
+
+        /**
+         * @brief Stop the timer
+         */
+        void stop();
+
+        /**
+         * @brief Returns true if the timer is running
+         */
+        bool running();
+
+        /**
+         * @brief Returns the timeout value
+         *
+         * @return - the last value sent in via start().
+         *
+         * Could be used to restart the timer with the same
+         * timeout.  i.e.  start(getTimeout());
+         */
+         inline auto getTimeout() const
+         {
+            return timeout;
+         }
+
+        /**
+         * @brief Returns the timer type
+         */
+        inline auto getType() const
+        {
+            return type;
+        }
+
+    private:
+
+        /**
+         * @brief Callback function when timer goes off
+         *
+         * Calls the callback function passed in by the user.
+         *
+         * @param[in] eventSource - Source of the event
+         * @param[in] usec        - time in micro seconds
+         * @param[in] userData    - User data pointer
+         */
+        static int timeoutHandler(sd_event_source* eventSource,
+                                  uint64_t usec, void* userData);
+
+        /**
+         * @brief Gets the current time from the steady clock
+         */
+        std::chrono::microseconds getTime();
+
+        /**
+         * @brief Wrapper around sd_event_source_set_enabled
+         *
+         * @param[in] action - either SD_EVENT_OFF, SD_EVENT_ON,
+         *                     or SD_EVENT_ONESHOT
+         */
+        void setTimer(int action);
+
+
+        /**
+         * @brief Sets the expiration time for the timer
+         *
+         * Sets it to timeout microseconds in the future
+         */
+        void setTimeout();
+
+        /**
+         * @brief The sd_event structure
+         */
+        EventPtr timeEvent;
+
+        /**
+         * @brief Source of events
+         */
+        EventSourcePtr eventSource;
+
+        /**
+         * @brief Either 'repeating' or 'oneshot'
+         */
+        TimerType type = TimerType::oneshot;
+
+        /**
+         * @brief The function to call when the timer expires
+         */
+        std::function<void()> callback;
+
+        /**
+         * @brief What the timer was set to run for
+         *
+         * Not cleared on timer expiration
+         */
+        std::chrono::microseconds timeout;
+};
+
+}
+}
+}