Latency monitor: basic samples collection.

src/latency.h

@@ -0,0 +1,42 @@
+#ifndef __LATENCY_H
+#define __LATENCY_H
+
+#define LATENCY_TS_LEN 160 /* History length for every monitored event. */
+
+/* Representation of a latency sample: the sampling time and the latency
+ * observed in milliseconds. */
+struct latencySample {
+    int32_t time; /* We don't use time_t to force 4 bytes usage everywhere. */
+    uint32_t latency; /* Latency in milliseconds. */
+};
+
+/* The latency time series for a given event. */
+struct latencyTimeSeries {
+    int idx; /* Index of the next sample to store. */
+    mstime_t max; /* Max latency observed for this event. */
+    struct latencySample samples[LATENCY_TS_LEN]; /* Latest history. */
+};
+
+void latencyMonitorInit(void);
+void latencyAddSample(char *event, mstime_t latency);
+
+/* Latency monitoring macros. */
+
+/* Start monitoring an event. We just set the current time. */
+#define latencyStartMonitor(var) if (server.latency_monitor_threshold) { \
+    var = mstime(); \
+}
+
+/* End monitoring an event, compute the difference with the current time
+ * to check the amount of time elapsed. */
+#define latencyEndMonitor(var) if (server.latency_monitor_threshold) { \
+    var = mstime() - var; \
+}
+
+/* Add the sample only if the elapsed time is >= to the configured threshold. */
+#define latencyAddSampleIfNeeded(event,var) \
+    if (server.latency_monitor_threshold && \\
+        var >= server.latency_monitor_threshold) \
+          latencyAddSample(event,var);
+
+#endif /* __LATENCY_H */