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diff --git a/ctdb/common/hash_count.h b/ctdb/common/hash_count.h
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+/*
+   Using hash table for counting events
+
+   Copyright (C) Amitay Isaacs  2017
+
+   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/>.
+*/
+
+#ifndef __CTDB_HASH_COUNT_H__
+#define __CTDB_HASH_COUNT_H__
+
+/**
+ * @file hash_count.h
+ *
+ * @brief Count key-based events for specified interval
+ *
+ * This can be used to measure the rate of events based on any interval.
+ * For example, number of occurrences per second.
+ */
+
+/**
+ * @brief Handler callback function called when counter is incremented
+ *
+ * This function is called every time a counter is incremented for a key.
+ * The counter argument is the number of times the increment function is
+ * called during a count interval.
+ *
+ * This function should not modify key and data arguments.
+ */
+typedef void (*hash_count_update_handler_fn)(TDB_DATA key, uint64_t counter,
+					     void *private_data);
+
+/**
+ * @brief Abstract structure representing hash based counting
+ */
+struct hash_count_context;
+
+/**
+ * @brief Initialize hash counting
+ *
+ * This return a new hash count context which is a talloc context.  Freeing
+ * this context will free all the memory associated with hash count.
+ *
+ * @param[in] mem_ctx Talloc memory context
+ * @param[in] count_interval The time interval for counting events
+ * @param[in] handler Function called when counter is incremented
+ * @param[in] private_data Private data to handler function
+ * @param[out] result The new hash_count structure
+ * @return 0 on success, errno on failure
+ */
+int hash_count_init(TALLOC_CTX *mem_ctx, struct timeval count_interval,
+		    hash_count_update_handler_fn handler, void *private_data,
+		    struct hash_count_context **result);
+
+/**
+ * @brief Increment a counter for a key
+ *
+ * First time this is called for a key, corresponding counter is set to 1
+ * and the start time is noted.  For all subsequent calls made during the
+ * count_interval (used in initializing the context) will increment
+ * corresponding counter for the key.  After the count_interval has elapsed,
+ * the counter will be reset to 1.
+ *
+ * @param[in] hcount The hash count context
+ * @param[in] key The key for which counter is updated
+ * @return 0 on success, errno on failure
+ *
+ * This will result in a callback function being called.
+ */
+int hash_count_increment(struct hash_count_context *hcount, TDB_DATA key);
+
+/**
+ * @brief Remove keys for which count interval has elapsed
+ *
+ * This function is used to clean the database of keys for which there are
+ * no recent events.
+ *
+ * @param[in] hcount The hash count context
+ * @param[out] delete_count The number of keys deleted
+ */
+void hash_count_expire(struct hash_count_context *hcount, int *delete_count);
+
+#endif /* __CTDB_HASH_COUNT_H__ */