From 5c37868e54ee04f51987477e2b87632fc49501f3 Mon Sep 17 00:00:00 2001
From: José Bollo <jose.bollo@iot.bzh>
Date: Wed, 29 Nov 2017 18:02:23 +0100
Subject: jobs: rewrite of the event loop handling
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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This new version use an eventfd to unlock the
event loop when needed. This reduce the count
of sd_event needed.
Bug-AGL: SPEC-1091
Change-Id: I9bc273e89ab1a70ccc2187c2571e68c9c771ee25
Signed-off-by: José Bollo <jose.bollo@iot.bzh>
---
src/jobs.c | 214 +++++++++++++++++++++++++++++++------------------------------
1 file changed, 108 insertions(+), 106 deletions(-)
diff --git a/src/jobs.c b/src/jobs.c
index 508d1b8e..464f1e11 100644
--- a/src/jobs.c
+++ b/src/jobs.c
@@ -26,6 +26,7 @@
#include <pthread.h>
#include <errno.h>
#include <assert.h>
+#include <sys/eventfd.h>
#include <systemd/sd-event.h>
@@ -59,18 +60,18 @@ struct job
};
/** Description of handled event loops */
-struct events
+struct evloop
{
- struct events *next;
- struct sd_event *event;
- uint64_t timeout;
- enum {
- Available,
- Modifiable,
- Locked
- } state;
+ unsigned state; /**< encoded state */
+ int efd; /**< event notification */
+ struct sd_event *sdev; /**< the systemd event loop */
+ pthread_cond_t cond; /**< condition */
};
+#define EVLOOP_STATE_WAIT 1U
+#define EVLOOP_STATE_RUN 2U
+#define EVLOOP_STATE_LOCK 4U
+
/** Description of threads */
struct thread
{
@@ -101,23 +102,24 @@ struct sync
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
-/* count allowed, started and waiting threads */
+/* count allowed, started and running threads */
static int allowed = 0; /** allowed count of threads */
static int started = 0; /** started count of threads */
-static int waiting = 0; /** waiting count of threads */
+static int running = 0; /** running count of threads */
static int remains = 0; /** allowed count of waiting jobs */
-static int nevents = 0; /** count of events */
/* list of threads */
static struct thread *threads;
static _Thread_local struct thread *current_thread;
-static _Thread_local struct events *current_events;
+static _Thread_local struct evloop *current_evloop;
/* queue of pending jobs */
static struct job *first_job;
-static struct events *first_events;
static struct job *free_jobs;
+/* event loop */
+static struct evloop evloop[1];
+
/**
* Create a new job with the given parameters
* @param group the group of the job
@@ -199,18 +201,6 @@ static inline struct job *job_get()
return job;
}
-/**
- * Get the next events to process or NULL if none.
- * @return the first events that isn't running or NULL
- */
-static inline struct events *events_get()
-{
- struct events *events = first_events;
- while (events && events->state != Available)
- events = events->next;
- return events;
-}
-
/**
* Releases the processed 'job': removes it
* from the list of jobs and unblock the first
@@ -272,38 +262,41 @@ static void job_cancel(int signum, void *arg)
* flow
* @param arg the events to run
*/
-static void events_call(int signum, void *arg)
+static void evloop_run(int signum, void *arg)
{
int rc;
struct sd_event *se;
- struct events *events = arg;
+ struct evloop *el = arg;
if (!signum) {
- se = events->event;
+ se = el->sdev;
rc = sd_event_prepare(se);
if (rc < 0) {
errno = -rc;
- ERROR("sd_event_prepare returned an error (state: %d): %m", sd_event_get_state(events->event));
+ ERROR("sd_event_prepare returned an error (state: %d): %m", sd_event_get_state(se));
} else {
if (rc == 0) {
- rc = sd_event_wait(se, events->timeout);
+ rc = sd_event_wait(se, (uint64_t)(int64_t)-1);
if (rc < 0) {
errno = -rc;
- ERROR("sd_event_wait returned an error (state: %d): %m", sd_event_get_state(events->event));
+ ERROR("sd_event_wait returned an error (state: %d): %m", sd_event_get_state(se));
}
}
+ el->state &= ~(EVLOOP_STATE_WAIT);
if (rc > 0) {
rc = sd_event_dispatch(se);
if (rc < 0) {
errno = -rc;
- ERROR("sd_event_dispatch returned an error (state: %d): %m", sd_event_get_state(events->event));
+ ERROR("sd_event_dispatch returned an error (state: %d): %m", sd_event_get_state(se));
}
}
}
}
+ el->state &= ~(EVLOOP_STATE_WAIT|EVLOOP_STATE_RUN);
}
+
/**
* Main processing loop of threads processing jobs.
* The loop must be called with the mutex locked
@@ -315,20 +308,16 @@ static void thread_run(volatile struct thread *me)
{
struct thread **prv;
struct job *job;
- struct events *events;
- uint64_t evto;
+ struct evloop *el;
/* initialize description of itself and link it in the list */
me->tid = pthread_self();
me->stop = 0;
me->waits = 0;
me->upper = current_thread;
- if (current_thread) {
- evto = EVENT_TIMEOUT_CHILD;
- } else {
+ if (!current_thread) {
started++;
sig_monitor_init_timeouts();
- evto = EVENT_TIMEOUT_TOP;
}
me->next = threads;
threads = (struct thread*)me;
@@ -336,6 +325,12 @@ static void thread_run(volatile struct thread *me)
/* loop until stopped */
while (!me->stop) {
+ /* release the event loop */
+ if (current_evloop && !(current_evloop->state & EVLOOP_STATE_RUN)) {
+ current_evloop->state -= EVLOOP_STATE_LOCK;
+ current_evloop = NULL;
+ }
+
/* get a job */
job = job_get(first_job);
if (job) {
@@ -349,41 +344,27 @@ static void thread_run(volatile struct thread *me)
sig_monitor(job->timeout, job->callback, job->arg);
pthread_mutex_lock(&mutex);
- /* release event if any */
- events = current_events;
- if (events && events->state == Modifiable) {
- current_events = NULL;
- events->state = Available;
- }
-
/* release the run job */
job_release(job);
} else {
/* no job, check events */
- events = current_events;
- if (!events)
- events = events_get();
- else if (events->state == Locked) {
- events = 0;
- WARNING("Loosing an event loop because reentering");
- }
- if (events) {
+ el = &evloop[0];
+ if (el->sdev && !el->state) {
/* run the events */
- events->state = Locked;
- events->timeout = evto;
- current_events = events;
+ el->state = EVLOOP_STATE_LOCK|EVLOOP_STATE_RUN|EVLOOP_STATE_WAIT;
+ current_evloop = el;
pthread_mutex_unlock(&mutex);
- sig_monitor(0, events_call, events);
+ sig_monitor(0, evloop_run, el);
pthread_mutex_lock(&mutex);
- current_events = NULL;
- events->state = Available;
} else {
/* no job and not events */
- waiting++;
+ running--;
+ if (!running)
+ ERROR("Entering job deep sleep! Check your bindings.");
me->waits = 1;
pthread_cond_wait(&cond, &mutex);
me->waits = 0;
- waiting--;
+ running++;
}
}
}
@@ -410,7 +391,9 @@ static void *thread_main(void *data)
struct thread me;
pthread_mutex_lock(&mutex);
+ running++;
thread_run(&me);
+ running--;
pthread_mutex_unlock(&mutex);
return NULL;
}
@@ -478,7 +461,7 @@ int jobs_queue(
}
/* start a thread if needed */
- if (waiting == 0 && started < allowed) {
+ if (running == started && started < allowed) {
/* all threads are busy and a new can be started */
rc = start_one_thread();
if (rc < 0 && started == 0) {
@@ -642,62 +625,81 @@ int jobs_call(
return do_sync(group, timeout, call_cb, &sync);
}
+/**
+ * Internal callback for evloop management.
+ * The effect of this function is hidden: it exits
+ * the waiting poll if any. Then it wakes up a thread
+ * awaiting the evloop using signal.
+ */
+static int on_evloop_efd(sd_event_source *s, int fd, uint32_t revents, void *userdata)
+{
+ uint64_t x;
+ struct evloop *evloop = userdata;
+ read(evloop->efd, &x, sizeof x);
+ pthread_cond_signal(&evloop->cond);
+ return 1;
+}
+
/**
* Gets a sd_event item for the current thread.
* @return a sd_event or NULL in case of error
*/
struct sd_event *jobs_get_sd_event()
{
- struct events *events;
+ struct evloop *el;
+ uint64_t x;
int rc;
pthread_mutex_lock(&mutex);
- /* search events on stack */
- events = current_events;
- if (!events) {
- /* search an available events */
- events = events_get();
- if (!events) {
- /* not found, check if creation possible */
- if (nevents >= allowed) {
- ERROR("not possible to add a new event");
- events = NULL;
- } else {
- events = malloc(sizeof *events);
- if (events && (rc = sd_event_new(&events->event)) >= 0) {
- if (nevents < started || start_one_thread() >= 0) {
- events->state = Available;
- events->next = first_events;
- first_events = events;
- } else {
- ERROR("can't start thread for events");
- sd_event_unref(events->event);
- free(events);
- events = NULL;
- }
- } else {
- if (!events) {
- ERROR("out of memory");
- errno = ENOMEM;
- } else {
- free(events);
- ERROR("creation of sd_event failed: %m");
- events = NULL;
- errno = -rc;
- }
- }
- }
+ /* creates the evloop on need */
+ el = &evloop[0];
+ if (!el->sdev) {
+ /* creates the eventfd for waking up polls */
+ el->efd = eventfd(0, EFD_CLOEXEC|EFD_SEMAPHORE);
+ if (el->efd < 0) {
+ ERROR("can't make eventfd for events");
+ goto error1;
}
- if (events) {
- events->state = Modifiable;
- if (!current_thread)
- WARNING("event returned for unknown thread!");
- current_events = events;
+ /* create the systemd event loop */
+ rc = sd_event_new(&el->sdev);
+ if (rc < 0) {
+ ERROR("can't make new event loop");
+ goto error2;
}
+ /* put the eventfd in the event loop */
+ rc = sd_event_add_io(el->sdev, NULL, el->efd, EPOLLIN, on_evloop_efd, el);
+ if (rc < 0) {
+ ERROR("can't register eventfd");
+ sd_event_unref(el->sdev);
+ el->sdev = NULL;
+error2:
+ close(el->efd);
+error1:
+ pthread_mutex_unlock(&mutex);
+ return NULL;
+ }
+ /* terminate creation */
+ el->state = 0;
+ }
+
+ /* attach the event loop to the current thread */
+ if (current_evloop != el) {
+ if (current_evloop)
+ current_evloop->state -= EVLOOP_STATE_LOCK;
+ current_evloop = el;
+ el->state += EVLOOP_STATE_LOCK;
+ }
+
+ /* wait for a modifiable event loop */
+ while (el->state & EVLOOP_STATE_WAIT) {
+ x = 1;
+ write(el->efd, &x, sizeof x);
+ pthread_cond_wait(&el->cond, &mutex);
}
+
pthread_mutex_unlock(&mutex);
- return events ? events->event : NULL;
+ return el->sdev;
}
/**
@@ -738,7 +740,7 @@ int jobs_start(int allowed_count, int start_count, int waiter_count, void (*star
/* records the allowed count */
allowed = allowed_count;
started = 0;
- waiting = 0;
+ running = 0;
remains = waiter_count;
/* start at least one thread */
--
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