Add uc_restart_counter concept

include/ucore/restart_counter.h

@@ -0,0 +1,81 @@
+#ifndef UC_RESTART_COUNTER_H_
+#define UC_RESTART_COUNTER_H_
+/** @file
+ * Simple support for keeping track of number of restarts.
+ *
+ * Certain protocols desire support for comminicating the number
+ * of times an entity has restarted. 
+ * The counter might also serve as a seed for sequence number generation
+ * to minimize recycling a recently used sequence number.
+ *
+ * The number of times a process has been restarted is simply kept 
+ * track of via a counter in a restart state ile in ascii representation.
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif 
+
+struct UCRestartCounter {
+    unsigned int counter;
+    int fd;
+};
+
+typedef enum {
+    UC_RC_OK,
+    /** accessing the file failed, inspect errno
+     * for more info */
+    UC_RC_ERR_FILE_ACCESS_ERROR,
+    /* The file existed and is opened but
+     * no valid number could be read from the file.
+     * This is a transient error,
+     * the now new counter is initialized to 0, and
+     * written to the file */
+    UC_RC_ERR_FILE_CONTENT_ERROR,
+    /* UC_RC_FL_LOCK_FILE was specified but the file 
+     * is already locked by some other process */
+    UC_RC_ERR_FILE_LOCKED,
+    /** unspecified error. Inspect errno. */
+    UC_RC_ERR_UNSPECIFIED,
+    /** Given  by uc_restart_counter_close if the 
+     * file never was opened */
+    UC_RC_ERR_NOT_OPENED,
+} UCRCResult;
+
+/** Lock the restart state file and keep it open.
+ * e.g. to prevent several processes from being started
+ * and  using the same restart state file.*/
+#define UC_RC_FL_LOCK_FILE ( 1 << 0)
+
+/** Read and update the current restart counter.
+ * This is typically called once at program startup.
+ * 
+ * @param counter the counter to initialize
+ * @param filename the filename to use to keep track of the state
+ * @param flags one of UC_RC_FL_XX
+ */
+UCRCResult uc_restart_counter_init(
+                                   struct UCRestartCounter *counter, 
+                                   const char *filename,
+                                   unsigned int flags);
+
+/** Close the current restart counter file if it was opened with the 
+ * UC_RC_FL_LOCK_FILE flag.
+ *
+ * @counter counter file to close. (uc_restart_counter can still be called 
+ *          after * the file is closed)
+ * @return UC_RC_OK or if the file was not kept open with UC_RC_ERR_FILE_LOCKED
+ */        
+UCRCResult uc_restart_counter_close(struct UCRestartCounter *counter);
+
+/** Get the current restart counter.
+ * In case uc_restart_counter_init failed, this will return 0.
+ */
+unsigned int uc_restart_counter_get(const struct UCRestartCounter *counter);
+
+
+#ifdef __cplusplus
+}
+#endif 
+
+#endif