Sessiond timer thread

[lttng-tools.git] / src / bin / lttng-sessiond / sessiond-timer.c

/*
 * Copyright (C) 2017 - Julien Desfossez <jdesfossez@efficios.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License, version 2 only, as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#define _LGPL_SOURCE
#include <assert.h>
#include <inttypes.h>
#include <signal.h>

#include "sessiond-timer.h"
#include "health-sessiond.h"
#include "rotation-thread.h"

static
struct timer_signal_data timer_signal = {
	.tid = 0,
	.qs_done = 0,
	.lock = PTHREAD_MUTEX_INITIALIZER,
};

/*
 * Set custom signal mask to current thread.
 */
static
void setmask(sigset_t *mask)
{
	int ret;

	ret = sigemptyset(mask);
	if (ret) {
		PERROR("sigemptyset");
	}
	ret = sigaddset(mask, LTTNG_SESSIOND_SIG_TEARDOWN);
	if (ret) {
		PERROR("sigaddset teardown");
	}
	ret = sigaddset(mask, LTTNG_SESSIOND_SIG_EXIT);
	if (ret) {
		PERROR("sigaddset exit");
	}
}

/*
 * This is the same function as consumer_timer_signal_thread_qs, when it
 * returns, it means that no timer signr is currently pending or being handled
 * by the timer thread. This cannot be called from the timer thread.
 */
static
void sessiond_timer_signal_thread_qs(unsigned int signr)
{
	sigset_t pending_set;
	int ret;

	/*
	 * We need to be the only thread interacting with the thread
	 * that manages signals for teardown synchronization.
	 */
	pthread_mutex_lock(&timer_signal.lock);

	/* Ensure we don't have any signal queued for this session. */
	for (;;) {
		ret = sigemptyset(&pending_set);
		if (ret == -1) {
			PERROR("sigemptyset");
		}
		ret = sigpending(&pending_set);
		if (ret == -1) {
			PERROR("sigpending");
		}
		if (!sigismember(&pending_set, signr)) {
			break;
		}
		caa_cpu_relax();
	}

	/*
	 * From this point, no new signal handler will be fired that would try to
	 * access "session". However, we still need to wait for any currently
	 * executing handler to complete.
	 */
	cmm_smp_mb();
	CMM_STORE_SHARED(timer_signal.qs_done, 0);
	cmm_smp_mb();

	/*
	 * Kill with LTTNG_SESSIOND_SIG_TEARDOWN, so signal management thread
	 * wakes up.
	 */
	kill(getpid(), LTTNG_SESSIOND_SIG_TEARDOWN);

	while (!CMM_LOAD_SHARED(timer_signal.qs_done)) {
		caa_cpu_relax();
	}
	cmm_smp_mb();

	pthread_mutex_unlock(&timer_signal.lock);
}

/*
 * Start a timer on a session that will fire at a given interval
 * (timer_interval_us) and fire a given signal (signal).
 *
 * Returns a negative value on error, 0 if a timer was created, and
 * a positive value if no timer was created (not an error).
 */
static
int session_timer_start(timer_t *timer_id, struct ltt_session *session,
		unsigned int timer_interval_us, int signal, bool one_shot)
{
	int ret = 0, delete_ret;
	struct sigevent sev;
	struct itimerspec its;

	assert(session);

	sev.sigev_notify = SIGEV_SIGNAL;
	sev.sigev_signo = signal;
	sev.sigev_value.sival_ptr = session;
	ret = timer_create(CLOCKID, &sev, timer_id);
	if (ret == -1) {
		PERROR("timer_create");
		goto end;
	}

	its.it_value.tv_sec = timer_interval_us / 1000000;
	its.it_value.tv_nsec = (timer_interval_us % 1000000) * 1000;
	if (one_shot) {
		its.it_interval.tv_sec = 0;
		its.it_interval.tv_nsec = 0;
	} else {
		its.it_interval.tv_sec = its.it_value.tv_sec;
		its.it_interval.tv_nsec = its.it_value.tv_nsec;
	}

	ret = timer_settime(*timer_id, 0, &its, NULL);
	if (ret == -1) {
		PERROR("timer_settime");
		goto error_destroy_timer;
	}
	goto end;

error_destroy_timer:
	delete_ret = timer_delete(*timer_id);
	if (delete_ret == -1) {
		PERROR("timer_delete");
	}

end:
	return ret;
}

static
int session_timer_stop(timer_t *timer_id, int signal)
{
	int ret = 0;

	ret = timer_delete(*timer_id);
	if (ret == -1) {
		PERROR("timer_delete");
		goto end;
	}

	sessiond_timer_signal_thread_qs(signal);
	*timer_id = 0;
end:
	return ret;
}

/*
 * Block the RT signals for the entire process. It must be called from the
 * sessiond main before creating the threads
 */
int sessiond_timer_signal_init(void)
{
	int ret;
	sigset_t mask;

	/* Block signal for entire process, so only our thread processes it. */
	setmask(&mask);
	ret = pthread_sigmask(SIG_BLOCK, &mask, NULL);
	if (ret) {
		errno = ret;
		PERROR("pthread_sigmask");
		return -1;
	}
	return 0;
}

/*
 * This thread is the sighandler for the timer signals.
 */
void *sessiond_timer_thread(void *data)
{
	int signr;
	sigset_t mask;
	siginfo_t info;
	struct timer_thread_parameters *ctx = data;

	rcu_register_thread();
	rcu_thread_online();

	health_register(health_sessiond, HEALTH_SESSIOND_TYPE_TIMER);

	health_code_update();

	/* Only self thread will receive signal mask. */
	setmask(&mask);
	CMM_STORE_SHARED(timer_signal.tid, pthread_self());

	while (1) {
		health_code_update();

		health_poll_entry();
		signr = sigwaitinfo(&mask, &info);
		health_poll_exit();

		/*
		 * NOTE: cascading conditions are used instead of a switch case
		 * since the use of SIGRTMIN in the definition of the signals'
		 * values prevents the reduction to an integer constant.
		 */
		if (signr == -1) {
			if (errno != EINTR) {
				PERROR("sigwaitinfo");
			}
			continue;
		} else if (signr == LTTNG_SESSIOND_SIG_TEARDOWN) {
			cmm_smp_mb();
			CMM_STORE_SHARED(timer_signal.qs_done, 1);
			cmm_smp_mb();
			DBG("Signal timer metadata thread teardown");
		} else if (signr == LTTNG_SESSIOND_SIG_EXIT) {
			goto end;
		} else {
			ERR("Unexpected signal %d\n", info.si_signo);
		}
	}

end:
	DBG("[timer-thread] Exit");
	health_unregister(health_sessiond);
	rcu_thread_offline();
	rcu_unregister_thread();
	return NULL;
}