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threadpool: improve cooperative downsizing #4293

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Merged
merged 1 commit into from
Nov 30, 2024
Merged

threadpool: improve cooperative downsizing #4293

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1 change: 1 addition & 0 deletions ChangeLog
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
- make `subsample-mode=on` and `lossless=true` mutually exclusive [kleisauke]
- fix SZI write with openslide4 [goran-hc]
- heifsave: prevent use of AV1 intra block copy feature [lovell]
- threadpool: improve cooperative downsizing [kleisauke]

10/10/24 8.16.0

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22 changes: 14 additions & 8 deletions libvips/iofuncs/threadpool.c
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Original file line number Diff line number Diff line change
Expand Up @@ -270,18 +270,18 @@ typedef struct _VipsThreadpool {
*/
int n_waiting; // (atomic)

/* Increment this and the next worker will decrement and exit if needed
* (used to downsize the threadpool).
*/
int exit; // (atomic)

/* Set this to abort evaluation early with an error.
*/
gboolean error;

/* Ask threads to exit, either set by allocate, or on free.
*/
gboolean stop;

/* Set this and the next worker to see it will clear the flag and exit
* (used to downsize the threadpool).
*/
gboolean exit; // (atomic)
} VipsThreadpool;

static int
Expand Down Expand Up @@ -325,14 +325,20 @@ vips_worker_work_unit(VipsWorker *worker)

/* Has a thread been asked to exit? Volunteer if yes.
*/
if (g_atomic_int_compare_and_exchange(&pool->exit, TRUE, FALSE)) {
if (g_atomic_int_add(&pool->exit, -1) > 0) {
/* A thread had been asked to exit, and we've grabbed the
* flag.
*/
worker->stop = TRUE;
g_mutex_unlock(pool->allocate_lock);
return;
}
else {
/* No one had been asked to exit and we've mistakenly taken
* the exit count below zero. Put it back up again.
*/
g_atomic_int_inc(&pool->exit);
}

if (vips_worker_allocate(worker)) {
pool->error = TRUE;
Expand Down Expand Up @@ -513,7 +519,7 @@ vips_threadpool_new(VipsImage *im)
vips_semaphore_init(&pool->tick, 0, "tick");
pool->error = FALSE;
pool->stop = FALSE;
pool->exit = FALSE;
pool->exit = 0;

/* If this is a tiny image, we won't need all max_workers threads.
* Guess how
Expand Down Expand Up @@ -696,7 +702,7 @@ vips_threadpool_run(VipsImage *im,
if (n_waiting > 3 &&
n_working > 1) {
VIPS_DEBUG_MSG("shrinking thread pool\n");
g_atomic_int_set(&pool->exit, TRUE);
g_atomic_int_inc(&pool->exit);
n_working -= 1;
}
else if (n_waiting < 2 &&
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