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/* -----------------------------------------------------------------------------
*
* (c) The GHC Team, 1995-2007
*
* Interval timer for profiling and pre-emptive scheduling.
*
* ---------------------------------------------------------------------------*/
/*
* We use a realtime timer by default. I found this much more
* reliable than a CPU timer:
*
* Experiments with different frequencies: using
* CLOCK_REALTIME/CLOCK_MONOTONIC on Linux 2.6.32,
* 1000us has <1% impact on runtime
* 100us has ~2% impact on runtime
* 10us has ~40% impact on runtime
*
* using CLOCK_PROCESS_CPUTIME_ID on Linux 2.6.32,
* I cannot get it to tick faster than 10ms (10000us)
* which isn't great for profiling.
*
* In the threaded RTS, we can't tick in CPU time because the thread
* which has the virtual timer might be idle, so the tick would never
* fire. Therefore we used to tick in realtime in the threaded RTS and
* in CPU time otherwise, but now we always tick in realtime, for
* several reasons:
*
* - resolution (see above)
* - consistency (-threaded is the same as normal)
* - more consistency: Windows only has a realtime timer
*
* Note we want to use CLOCK_MONOTONIC rather than CLOCK_REALTIME,
* because the latter may jump around (NTP adjustments, leap seconds
* etc.).
*/
#include "PosixSource.h"
#include "Rts.h"
#include "Ticker.h"
#include "RtsUtils.h"
#include "Proftimer.h"
#include "Schedule.h"
#include "posix/Clock.h"
/* As recommended in the autoconf manual */
# if defined(TIME_WITH_SYS_TIME)
# include <sys/time.h>
# include <time.h>
# else
# if defined(HAVE_SYS_TIME_H)
# include <sys/time.h>
# else
# include <time.h>
# endif
# endif
#if defined(HAVE_SIGNAL_H)
# include <signal.h>
#endif
#include <string.h>
#include <pthread.h>
#include <unistd.h>
#include <fcntl.h>
#if defined(HAVE_SYS_TIMERFD_H)
#include <sys/timerfd.h>
#define USE_TIMERFD_FOR_ITIMER 1
#else
#define USE_TIMERFD_FOR_ITIMER 0
#endif
/*
* TFD_CLOEXEC has been added in Linux 2.6.26.
* If it is not available, we use fcntl(F_SETFD).
*/
#if !defined(TFD_CLOEXEC)
#define TFD_CLOEXEC 0
#endif
static Time itimer_interval = DEFAULT_TICK_INTERVAL;
// Should we be firing ticks?
// Writers to this must hold the mutex below.
static volatile bool stopped = false;
// should the ticker thread exit?
// This can be set without holding the mutex.
static volatile bool exited = true;
// Signaled when we want to (re)start the timer
static Condition start_cond;
static Mutex mutex;
static OSThreadId thread;
static void *itimer_thread_func(void *_handle_tick)
{
TickProc handle_tick = _handle_tick;
uint64_t nticks;
int timerfd = -1;
#if defined(USE_TIMERFD_FOR_ITIMER) && USE_TIMERFD_FOR_ITIMER
struct itimerspec it;
it.it_value.tv_sec = TimeToSeconds(itimer_interval);
it.it_value.tv_nsec = TimeToNS(itimer_interval) % 1000000000;
it.it_interval = it.it_value;
timerfd = timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC);
if (timerfd == -1) {
barf("timerfd_create: %s", strerror(errno));
}
if (!TFD_CLOEXEC) {
fcntl(timerfd, F_SETFD, FD_CLOEXEC);
}
if (timerfd_settime(timerfd, 0, &it, NULL)) {
barf("timerfd_settime: %s", strerror(errno));
}
#endif
while (!exited) {
if (USE_TIMERFD_FOR_ITIMER) {
ssize_t r = read(timerfd, &nticks, sizeof(nticks));
if ((r == 0) && (errno == 0)) {
/* r == 0 is expected only for non-blocking fd (in which case
* errno should be EAGAIN) but we use a blocking fd.
*
* Due to a kernel bug (cf https://lkml.org/lkml/2019/8/16/335)
* on some platforms we could see r == 0 and errno == 0.
*/
IF_DEBUG(scheduler, debugBelch("read(timerfd) returned 0 with errno=0. This is a known kernel bug. We just ignore it."));
}
else if (r != sizeof(nticks) && errno != EINTR) {
barf("Itimer: read(timerfd) failed with %s and returned %zd", strerror(errno), r);
}
} else {
if (rtsSleep(itimer_interval) != 0) {
sysErrorBelch("ITimer: sleep failed: %s", strerror(errno));
}
}
// first try a cheap test
if (stopped) {
OS_ACQUIRE_LOCK(&mutex);
// should we really stop?
if (stopped) {
waitCondition(&start_cond, &mutex);
}
OS_RELEASE_LOCK(&mutex);
} else {
handle_tick(0);
}
}
if (USE_TIMERFD_FOR_ITIMER)
close(timerfd);
return NULL;
}
void
initTicker (Time interval, TickProc handle_tick)
{
itimer_interval = interval;
stopped = false;
exited = false;
initCondition(&start_cond);
initMutex(&mutex);
/*
* We can't use the RTS's createOSThread here as we need to remain attached
* to the thread we create so we can later join to it if requested
*/
if (! pthread_create(&thread, NULL, itimer_thread_func, (void*)handle_tick)) {
#if defined(HAVE_PTHREAD_SETNAME_NP)
pthread_setname_np(thread, "ghc_ticker");
#endif
} else {
barf("Itimer: Failed to spawn thread: %s", strerror(errno));
}
}
void
startTicker(void)
{
OS_ACQUIRE_LOCK(&mutex);
stopped = 0;
signalCondition(&start_cond);
OS_RELEASE_LOCK(&mutex);
}
/* There may be at most one additional tick fired after a call to this */
void
stopTicker(void)
{
OS_ACQUIRE_LOCK(&mutex);
stopped = 1;
OS_RELEASE_LOCK(&mutex);
}
/* There may be at most one additional tick fired after a call to this */
void
exitTicker (bool wait)
{
ASSERT(!exited);
exited = true;
// ensure that ticker wakes up if stopped
startTicker();
// wait for ticker to terminate if necessary
if (wait) {
if (pthread_join(thread, NULL)) {
sysErrorBelch("Itimer: Failed to join: %s", strerror(errno));
}
closeMutex(&mutex);
closeCondition(&start_cond);
} else {
pthread_detach(thread);
}
}
int
rtsTimerSignal(void)
{
return SIGALRM;
}
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