cc: extend duration module (twitter#192)

- add fast (low overhead) duration timers for linux
- add duration compare method

include/time/cc_timer.h

@@ -49,6 +49,14 @@ struct duration;  /* data structure to measure duration */
  *   relationship between this unit and nanosecond can be obtained via another
  *   syscall
  */
+
+enum duration_type {
+    DURATION_PRECISE, /* default */
+    DURATION_FAST,
+
+    MAX_DURATION_TYPE
+};
+
 #ifdef OS_DARWIN
 struct duration {
     bool        started;
@@ -58,6 +66,7 @@ struct duration {
 };
 #elif defined OS_LINUX
 struct duration {
+    enum duration_type type;
     bool            started;
     bool            stopped;
     struct timespec start;
@@ -86,19 +95,31 @@ struct timeout {
     bool        is_intvl;
 };
 
-
 /* update duration */
 void duration_reset(struct duration *d);
 /* get a reading of duration and copy it without stopping the original timer */
 void duration_snapshot(struct duration *s, const struct duration *d);
 void duration_start(struct duration *d);
+void duration_start_type(struct duration *d, enum duration_type type);
 void duration_stop(struct duration *d);
 /* read duration */
 double duration_ns(struct duration *d);
 double duration_us(struct duration *d);
 double duration_ms(struct duration *d);
 double duration_sec(struct duration *d);
 
+static inline int
+duration_compare(const void *lhs, const void *rhs)
+{
+    double lns = duration_ns((struct duration *)lhs);
+    double rns = duration_ns((struct duration *)rhs);
+    if (lns < rns)
+        return -1;
+    if (lns > rns)
+        return 1;
+
+    return 0;
+}
 
 /*
  * Not all possible granularity can be meaningfully used for sleep or event.

src/time/cc_timer_darwin.c

@@ -72,6 +72,12 @@ duration_start(struct duration *d)
     d->start = mach_absolute_time();
 }
 
+void
+duration_start_type(struct duration *d, enum duration_type type)
+{
+    duration_start(d);
+}
+
 void
 duration_stop(struct duration *d)
 {

src/time/cc_timer_linux.c

@@ -25,24 +25,35 @@
  * CLOCK_REALTIME can be reset when clock has drifted, so it may not always be
  * monotonic, and should be avoided if possible.
  */
+static const clockid_t cid[MAX_DURATION_TYPE] = {
+    [DURATION_PRECISE] =
 #if defined(CLOCK_MONOTONIC_RAW)
-static const clockid_t cid = CLOCK_MONOTONIC_RAW;
+        CLOCK_MONOTONIC_RAW
 #elif defined(CLOCK_MONOTONIC)
-static const clockid_t cid = CLOCK_MONOTONIC;
+        CLOCK_MONOTONIC
 #elif defined(CLOCK_REALTIME)
-static const clockid_t cid = CLOCK_REALTIME;
+        CLOCK_REALTIME
 #else
-static const clockid_t cid = (clockid_t)-1;
+        (clockid_t)-1
 #endif
+,
+#if defined(CLOCK_MONOTONIC)
+        CLOCK_MONOTONIC
+#elif defined(CLOCK_REALTIME)
+        CLOCK_REALTIME
+#else
+        (clockid_t)-1
+#endif
+};
 
 static inline void
-_gettime(struct timespec *ts)
+_gettime(struct timespec *ts, enum duration_type type)
 {
     int ret;
 
-    ASSERT(cid != (clockid_t)-1);
+    ASSERT(cid[type] != (clockid_t)-1);
 
-    ret = clock_gettime(cid, ts);
+    ret = clock_gettime(cid[type], ts);
     if (ret == -1) {
         /*
          * Note(yao): for the purpose of this module, it doesn't make much sense
@@ -73,10 +84,17 @@ duration_reset(struct duration *d)
 
 void
 duration_start(struct duration *d)
+{
+    duration_start_type(d, DURATION_PRECISE);
+}
+
+void
+duration_start_type(struct duration *d, enum duration_type type)
 {
     ASSERT(d != NULL);
 
-    _gettime(&d->start);
+    _gettime(&d->start, type);
+    d->type = type;
     d->started = true;
 }
 
@@ -87,16 +105,17 @@ duration_snapshot(struct duration *s, const struct duration *d)
 
     s->started = true;
     s->start = d->start;
+    s->type = d->type;
     s->stopped = true;
-    _gettime(&s->stop);
+    _gettime(&s->stop, s->type);
 }
 
 void
 duration_stop(struct duration *d)
 {
     ASSERT(d != NULL);
 
-    _gettime(&d->stop);
+    _gettime(&d->stop, d->type);
     d->stopped = true;
 }
 
@@ -153,9 +172,8 @@ _now_ns(void)
 {
     struct timespec now;
 
-    _gettime(&now);
+    _gettime(&now, cid[DURATION_PRECISE]);
     return now.tv_sec * NSEC_PER_SEC + now.tv_nsec;
-
 }
 
 void