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+/* Copyright (C) 2019 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+/*!
+ * \brief Event scheduler.
+ */
+
+#pragma once
+
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <sys/time.h>
+
+#include "knot/server/dthreads.h"
+#include "contrib/ucw/heap.h"
+
+/* Forward decls. */
+struct evsched;
+struct event;
+
+/*!
+ * \brief Event callback.
+ *
+ * Pointer to whole event structure is passed to the callback.
+ * Callback should return 0 on success and negative integer on error.
+ *
+ * Example callback:
+ * \code
+ * void print_callback(event_t *t) {
+ * printf("Callback: %s\n", t->data);
+ * }
+ * \endcode
+ */
+typedef void (*event_cb_t)(struct event *);
+
+/*!
+ * \brief Event structure.
+ */
+typedef struct event {
+ struct heap_val hpos;
+ struct timeval tv; /*!< Event scheduled time. */
+ void *data; /*!< Usable data ptr. */
+ event_cb_t cb; /*!< Event callback. */
+ struct evsched *sched; /*!< Scheduler for this event. */
+} event_t;
+
+/*!
+ * \brief Event scheduler structure.
+ */
+typedef struct evsched {
+ volatile bool paused; /*!< Temporarily stop processing events. */
+ pthread_mutex_t heap_lock; /*!< Event heap locking. */
+ pthread_cond_t notify; /*!< Event heap notification. */
+ struct heap heap; /*!< Event heap. */
+ void *ctx; /*!< Scheduler context. */
+ dt_unit_t *thread;
+} evsched_t;
+
+/*!
+ * \brief Initialize event scheduler instance.
+ *
+ * \retval New instance on success.
+ * \retval NULL on error.
+ */
+int evsched_init(evsched_t *sched, void *ctx);
+
+/*!
+ * \brief Deinitialize and free event scheduler instance.
+ *
+ * \param sched Pointer to event scheduler instance.
+ */
+void evsched_deinit(evsched_t *sched);
+
+/*!
+ * \brief Create a callback event.
+ *
+ * \note Scheduler takes ownership of scheduled events. Created, but unscheduled
+ * events are in the ownership of the caller.
+ *
+ * \param sched Pointer to event scheduler instance.
+ * \param cb Callback handler.
+ * \param data Data for callback.
+ *
+ * \retval New instance on success.
+ * \retval NULL on error.
+ */
+event_t *evsched_event_create(evsched_t *sched, event_cb_t cb, void *data);
+
+/*!
+ * \brief Dispose event instance.
+ *
+ * \param ev Event instance.
+ */
+void evsched_event_free(event_t *ev);
+
+/*!
+ * \brief Schedule an event.
+ *
+ * \note This function checks if the event was already scheduled, if it was
+ * then it replaces this timer with the newer value.
+ * Running events are not canceled or waited for.
+ *
+ * \param ev Prepared event.
+ * \param dt Time difference in milliseconds from now (dt is relative).
+ *
+ * \retval KNOT_EOK on success.
+ * \retval KNOT_EINVAL
+ */
+int evsched_schedule(event_t *ev, uint32_t dt);
+
+/*!
+ * \brief Cancel a scheduled event.
+ *
+ * \warning May block until current running event is finished (as it cannot
+ * interrupt running event).
+ *
+ * \warning Never cancel event in it's callback. As it never finishes,
+ * it deadlocks.
+ *
+ * \param ev Scheduled event.
+ *
+ * \retval KNOT_EOK
+ * \retval KNOT_EINVAL
+ */
+int evsched_cancel(event_t *ev);
+
+/*! \brief Start event processing threads. */
+void evsched_start(evsched_t *sched);
+
+/*! \brief Stop event processing threads. */
+void evsched_stop(evsched_t *sched);
+
+/*! \brief Join event processing threads. */
+void evsched_join(evsched_t *sched);
+
+/*! \brief Temporarily stop processing events. */
+void evsched_pause(evsched_t *sched);
+
+/*! \brief Resume processing events. */
+void evsched_resume(evsched_t *sched);