[ovs-dev] [threads 07/28] timeval: Make reading the current time thread-safe.
Ben Pfaff
blp at nicira.com
Wed Jul 10 23:03:49 UTC 2013
Signed-off-by: Ben Pfaff <blp at nicira.com>
---
lib/timeval.c | 217 +++++++++++++++++++++++++++++---------------------------
1 files changed, 112 insertions(+), 105 deletions(-)
diff --git a/lib/timeval.c b/lib/timeval.c
index a13b87d..b589cb9 100644
--- a/lib/timeval.c
+++ b/lib/timeval.c
@@ -18,6 +18,7 @@
#include "timeval.h"
#include <errno.h>
#include <poll.h>
+#include <pthread.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
@@ -47,30 +48,28 @@
VLOG_DEFINE_THIS_MODULE(timeval);
-/* The clock to use for measuring time intervals. This is CLOCK_MONOTONIC by
- * preference, but on systems that don't have a monotonic clock we fall back
- * to CLOCK_REALTIME. */
-static clockid_t monotonic_clock;
+struct clock {
+ clockid_t id; /* CLOCK_MONOTONIC or CLOCK_REALTIME. */
+ pthread_rwlock_t rwlock; /* Mutual exclusion for 'cache'. */
-/* Has a timer tick occurred? Only relevant if CACHE_TIME is true.
- *
- * We initialize these to true to force time_init() to get called on the first
- * call to time_msec() or another function that queries the current time. */
-static volatile sig_atomic_t wall_tick = true;
-static volatile sig_atomic_t monotonic_tick = true;
+ /* Features for use by unit tests. Protected by 'rwlock'. */
+ struct timespec warp; /* Offset added for unit tests. */
+ bool stopped; /* Disables real-time updates if true. */
+
+ /* Relevant only if CACHE_TIME is true. */
+ volatile sig_atomic_t tick; /* Has the timer ticked? Set by signal. */
+ struct timespec cache; /* Last time read from kernel. */
+};
-/* The current time, as of the last refresh. */
-static struct timespec wall_time;
-static struct timespec monotonic_time;
+/* Our clocks. */
+static struct clock monotonic_clock; /* CLOCK_MONOTONIC, if available. */
+static struct clock wall_clock; /* CLOCK_REALTIME. */
/* The monotonic time at which the time module was initialized. */
static long long int boot_time;
-/* features for use by unit tests. */
-static struct timespec warp_offset; /* Offset added to monotonic_time. */
-static bool time_stopped; /* Disables real-time updates, if true. */
-
-/* Time in milliseconds at which to die with SIGALRM (if not LLONG_MAX). */
+/* Monotonic time in milliseconds at which to die with SIGALRM (if not
+ * LLONG_MAX). */
static long long int deadline = LLONG_MAX;
struct trace {
@@ -89,8 +88,6 @@ static size_t trace_head = 0;
static void set_up_timer(void);
static void set_up_signal(int flags);
static void sigalrm_handler(int);
-static void refresh_wall_if_ticked(void);
-static void refresh_monotonic_if_ticked(void);
static void block_sigalrm(sigset_t *);
static void unblock_sigalrm(const sigset_t *);
static void log_poll_interval(long long int last_wakeup);
@@ -114,16 +111,19 @@ backtrace_symbols(void *const *buffer OVS_UNUSED, int size OVS_UNUSED)
}
#endif /* !USE_BACKTRACE */
-/* Initializes the timetracking module, if not already initialized. */
static void
-time_init(void)
+init_clock(struct clock *c, clockid_t id)
{
- static bool inited;
+ memset(c, 0, sizeof *c);
+ c->id = id;
+ xpthread_rwlock_init(&c->rwlock, NULL);
+ xclock_gettime(c->id, &c->cache);
+}
- if (inited) {
- return;
- }
- inited = true;
+static void
+do_init_time(void)
+{
+ struct timespec ts;
/* The implementation of backtrace() in glibc does some one time
* initialization which is not signal safe. This can cause deadlocks if
@@ -143,17 +143,22 @@ time_init(void)
coverage_init();
- if (!clock_gettime(CLOCK_MONOTONIC, &monotonic_time)) {
- monotonic_clock = CLOCK_MONOTONIC;
- } else {
- monotonic_clock = CLOCK_REALTIME;
- VLOG_DBG("monotonic timer not available");
- }
+ init_clock(&monotonic_clock, (!clock_gettime(CLOCK_MONOTONIC, &ts)
+ ? CLOCK_MONOTONIC
+ : CLOCK_REALTIME));
+ init_clock(&wall_clock, CLOCK_REALTIME);
+ boot_time = timespec_to_msec(&monotonic_clock.cache);
set_up_signal(SA_RESTART);
set_up_timer();
+}
- boot_time = time_msec();
+/* Initializes the timetracking module, if not already initialized. */
+static void
+time_init(void)
+{
+ static pthread_once_t once = PTHREAD_ONCE_INIT;
+ pthread_once(&once, do_init_time);
}
static void
@@ -178,7 +183,7 @@ set_up_timer(void)
return;
}
- if (timer_create(monotonic_clock, NULL, &timer_id)) {
+ if (timer_create(monotonic_clock.id, NULL, &timer_id)) {
VLOG_FATAL("timer_create failed (%s)", ovs_strerror(errno));
}
@@ -203,91 +208,102 @@ time_postfork(void)
set_up_timer();
}
-static void
-refresh_wall(void)
+/* Forces a refresh of the current time from the kernel. It is not usually
+ * necessary to call this function, since the time will be refreshed
+ * automatically at least every TIME_UPDATE_INTERVAL milliseconds. If
+ * CACHE_TIME is false, we will always refresh the current time so this
+ * function has no effect. */
+void
+time_refresh(void)
{
- time_init();
- xclock_gettime(CLOCK_REALTIME, &wall_time);
- wall_tick = false;
+ monotonic_clock.tick = wall_clock.tick = true;
}
static void
-refresh_monotonic(void)
+time_timespec__(struct clock *c, struct timespec *ts)
{
time_init();
-
- if (!time_stopped) {
- if (monotonic_clock == CLOCK_MONOTONIC) {
- xclock_gettime(monotonic_clock, &monotonic_time);
- } else {
- refresh_wall_if_ticked();
- monotonic_time = wall_time;
+ for (;;) {
+ /* Use the cached time by preference, but fall through if there's been
+ * a clock tick. */
+ xpthread_rwlock_rdlock(&c->rwlock);
+ if (c->stopped || !c->tick) {
+ timespec_add(ts, &c->cache, &c->warp);
+ xpthread_rwlock_unlock(&c->rwlock);
+ return;
}
- timespec_add(&monotonic_time, &monotonic_time, &warp_offset);
+ xpthread_rwlock_unlock(&c->rwlock);
- monotonic_tick = false;
+ /* Refresh the cache. */
+ xpthread_rwlock_wrlock(&c->rwlock);
+ if (c->tick) {
+ c->tick = false;
+ xclock_gettime(c->id, &c->cache);
+ }
+ xpthread_rwlock_unlock(&c->rwlock);
}
}
-/* Forces a refresh of the current time from the kernel. It is not usually
- * necessary to call this function, since the time will be refreshed
- * automatically at least every TIME_UPDATE_INTERVAL milliseconds. If
- * CACHE_TIME is false, we will always refresh the current time so this
- * function has no effect. */
+/* Stores a monotonic timer, accurate within TIME_UPDATE_INTERVAL ms, into
+ * '*ts'. */
void
-time_refresh(void)
+time_timespec(struct timespec *ts)
{
- wall_tick = monotonic_tick = true;
+ time_timespec__(&monotonic_clock, ts);
+}
+
+/* Stores the current time, accurate within TIME_UPDATE_INTERVAL ms, into
+ * '*ts'. */
+void
+time_wall_timespec(struct timespec *ts)
+{
+ time_timespec__(&wall_clock, ts);
+}
+
+static time_t
+time_sec__(struct clock *c)
+{
+ struct timespec ts;
+
+ time_timespec__(c, &ts);
+ return ts.tv_sec;
}
/* Returns a monotonic timer, in seconds. */
time_t
time_now(void)
{
- refresh_monotonic_if_ticked();
- return monotonic_time.tv_sec;
+ return time_sec__(&monotonic_clock);
}
/* Returns the current time, in seconds. */
time_t
time_wall(void)
{
- refresh_wall_if_ticked();
- return wall_time.tv_sec;
+ return time_sec__(&wall_clock);
+}
+
+static long long int
+time_msec__(struct clock *c)
+{
+ struct timespec ts;
+
+ time_timespec__(c, &ts);
+ return timespec_to_msec(&ts);
}
/* Returns a monotonic timer, in ms (within TIME_UPDATE_INTERVAL ms). */
long long int
time_msec(void)
{
- refresh_monotonic_if_ticked();
- return timespec_to_msec(&monotonic_time);
+ return time_msec__(&monotonic_clock);
}
/* Returns the current time, in ms (within TIME_UPDATE_INTERVAL ms). */
long long int
time_wall_msec(void)
{
- refresh_wall_if_ticked();
- return timespec_to_msec(&wall_time);
-}
-
-/* Stores a monotonic timer, accurate within TIME_UPDATE_INTERVAL ms, into
- * '*ts'. */
-void
-time_timespec(struct timespec *ts)
-{
- refresh_monotonic_if_ticked();
- *ts = monotonic_time;
-}
-
-/* Stores the current time, accurate within TIME_UPDATE_INTERVAL ms, into
- * '*ts'. */
-void
-time_wall_timespec(struct timespec *ts)
-{
- refresh_wall_if_ticked();
- *ts = wall_time;
+ return time_msec__(&wall_clock);
}
/* Configures the program to die with SIGALRM 'secs' seconds from now, if
@@ -398,8 +414,7 @@ time_poll(struct pollfd *pollfds, int n_pollfds, long long int timeout_when,
static void
sigalrm_handler(int sig_nr OVS_UNUSED)
{
- wall_tick = true;
- monotonic_tick = true;
+ monotonic_clock.tick = wall_clock.tick = true;
if (USE_BACKTRACE && CACHE_TIME) {
struct trace *trace = &traces[trace_head];
@@ -411,22 +426,6 @@ sigalrm_handler(int sig_nr OVS_UNUSED)
}
static void
-refresh_wall_if_ticked(void)
-{
- if (!CACHE_TIME || wall_tick) {
- refresh_wall();
- }
-}
-
-static void
-refresh_monotonic_if_ticked(void)
-{
- if (!CACHE_TIME || monotonic_tick) {
- refresh_monotonic();
- }
-}
-
-static void
block_sigalrm(sigset_t *oldsigs)
{
sigset_t sigalrm;
@@ -508,7 +507,9 @@ log_poll_interval(long long int last_wakeup)
{
long long int interval = time_msec() - last_wakeup;
- if (interval >= 1000 && !warp_offset.tv_sec && !warp_offset.tv_nsec) {
+ if (interval >= 1000
+ && !monotonic_clock.warp.tv_sec
+ && !monotonic_clock.warp.tv_nsec) {
const struct rusage *last_rusage = get_recent_rusage();
struct rusage rusage;
@@ -686,7 +687,10 @@ timeval_stop_cb(struct unixctl_conn *conn,
int argc OVS_UNUSED, const char *argv[] OVS_UNUSED,
void *aux OVS_UNUSED)
{
- time_stopped = true;
+ xpthread_rwlock_wrlock(&monotonic_clock.rwlock);
+ monotonic_clock.stopped = true;
+ xpthread_rwlock_unlock(&monotonic_clock.rwlock);
+
unixctl_command_reply(conn, NULL);
}
@@ -710,8 +714,11 @@ timeval_warp_cb(struct unixctl_conn *conn,
ts.tv_sec = msecs / 1000;
ts.tv_nsec = (msecs % 1000) * 1000 * 1000;
- timespec_add(&warp_offset, &warp_offset, &ts);
- timespec_add(&monotonic_time, &monotonic_time, &ts);
+
+ xpthread_rwlock_wrlock(&monotonic_clock.rwlock);
+ timespec_add(&monotonic_clock.warp, &monotonic_clock.warp, &ts);
+ xpthread_rwlock_unlock(&monotonic_clock.rwlock);
+
unixctl_command_reply(conn, "warped");
}
--
1.7.2.5
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