Merge branch '3632-async-backwards' into 'main'

isc_async_run() runs events in reverse order

Closes #3632

See merge request isc-projects/bind9!7000

lib/isc/async.c

@@ -47,7 +47,9 @@ isc_async_run(isc_loop_t *loop, isc_job_cb cb, void *cbarg) {
 
 	job = isc__job_new(loop, cb, cbarg);
 
-	/* Now send the half initialized job to loop queue */
+	/*
+	 * Now send the half-initialized job to the loop queue.
+	 */
 	LOCK(&loop->queue_lock);
 	ISC_LIST_APPEND(loop->queue_jobs, job, link);
 	UNLOCK(&loop->queue_lock);

lib/isc/include/isc/job.h

@@ -39,6 +39,11 @@ isc_job_run(isc_loopmgr_t *loopmgr, isc_job_cb cb, void *cbarg);
  * Schedule the job callback 'cb' to be run on the currently
  * running event loop.
  *
+ * Note: Because of the design of uv_idle_start(), if more than one
+ * job is posted at once, the jobs will be pushed onto a stack and
+ * executed in last-in-first-out order. To post events that are
+ * executed in order posted, use isc_async_run() instead.
+ *
  * Requires:
  *
  *\li	'loopmgr' is the active loop manager.

lib/isc/loop.c

@@ -191,9 +191,14 @@ queue_cb(uv_async_t *handle) {
 	ISC_LIST_MOVE(list, loop->queue_jobs);
 	UNLOCK(&loop->queue_lock);
 
-	job = ISC_LIST_HEAD(list);
+	/*
+	 * The ISC_LIST_TAIL is counterintuitive here, but uv_idle
+	 * drains its queue backwards, so if there's more than one event to
+	 * be processed then they need to be in reverse order.
+	 */
+	job = ISC_LIST_TAIL(list);
 	while (job != NULL) {
-		isc_job_t *next = ISC_LIST_NEXT(job, link);
+		isc_job_t *next = ISC_LIST_PREV(job, link);
 		ISC_LIST_UNLINK(list, job, link);
 
 		isc__job_init(loop, job);

tests/isc/async_test.c

@@ -39,9 +39,10 @@ static atomic_uint scheduled = 0;
 
 static void
 async_cb(void *arg) {
-	UNUSED(arg);
 	uint32_t tid = isc_tid();
 
+	UNUSED(arg);
+
 	atomic_fetch_add(&scheduled, 1);
 
 	if (tid > 0) {
@@ -54,11 +55,11 @@ async_cb(void *arg) {
 
 static void
 async_setup_cb(void *arg) {
-	UNUSED(arg);
 	uint32_t tid = isc_loopmgr_nloops(loopmgr) - 1;
-
 	isc_loop_t *loop = isc_loop_get(loopmgr, tid);
 
+	UNUSED(arg);
+
 	isc_async_run(loop, async_cb, loopmgr);
 }
 
@@ -68,8 +69,40 @@ ISC_RUN_TEST_IMPL(isc_async_run) {
 	assert_int_equal(atomic_load(&scheduled), loopmgr->nloops);
 }
 
+static char string[32] = "";
+int n1 = 1, n2 = 2, n3 = 3, n4 = 4, n5 = 5;
+
+static void
+append(void *arg) {
+	char value[32];
+	sprintf(value, "%d", *(int *)arg);
+	strlcat(string, value, 10);
+}
+
+static void
+async_multiple(void *arg) {
+	isc_loop_t *loop = isc_loop_current(loopmgr);
+
+	UNUSED(arg);
+
+	isc_async_run(loop, append, &n1);
+	isc_async_run(loop, append, &n2);
+	isc_async_run(loop, append, &n3);
+	isc_async_run(loop, append, &n4);
+	isc_async_run(loop, append, &n5);
+	isc_loopmgr_shutdown(loopmgr);
+}
+
+ISC_RUN_TEST_IMPL(isc_async_multiple) {
+	string[0] = '\0';
+	isc_loop_setup(isc_loop_main(loopmgr), async_multiple, loopmgr);
+	isc_loopmgr_run(loopmgr);
+	assert_string_equal(string, "12345");
+}
+
 ISC_TEST_LIST_START
 ISC_TEST_ENTRY_CUSTOM(isc_async_run, setup_loopmgr, teardown_loopmgr)
+ISC_TEST_ENTRY_CUSTOM(isc_async_multiple, setup_loopmgr, teardown_loopmgr)
 ISC_TEST_LIST_END
 
 ISC_TEST_MAIN

tests/isc/job_test.c

@@ -76,8 +76,39 @@ ISC_RUN_TEST_IMPL(isc_job_run) {
 	assert_int_equal(atomic_load(&scheduled), atomic_load(&executed));
 }
 
+static char string[32] = "";
+int n1 = 1, n2 = 2, n3 = 3, n4 = 4, n5 = 5;
+
+static void
+append(void *arg) {
+	char value[32];
+	sprintf(value, "%d", *(int *)arg);
+	strlcat(string, value, 10);
+}
+
+static void
+job_multiple(void *arg) {
+	UNUSED(arg);
+
+	/* These will be processed in reverse order */
+	isc_job_run(loopmgr, append, &n1);
+	isc_job_run(loopmgr, append, &n2);
+	isc_job_run(loopmgr, append, &n3);
+	isc_job_run(loopmgr, append, &n4);
+	isc_job_run(loopmgr, append, &n5);
+	isc_loopmgr_shutdown(loopmgr);
+}
+
+ISC_RUN_TEST_IMPL(isc_job_multiple) {
+	string[0] = '\0';
+	isc_loop_setup(isc_loop_main(loopmgr), job_multiple, loopmgr);
+	isc_loopmgr_run(loopmgr);
+	assert_string_equal(string, "54321");
+}
+
 ISC_TEST_LIST_START
 ISC_TEST_ENTRY_CUSTOM(isc_job_run, setup_loopmgr, teardown_loopmgr)
+ISC_TEST_ENTRY_CUSTOM(isc_job_multiple, setup_loopmgr, teardown_loopmgr)
 ISC_TEST_LIST_END
 
 ISC_TEST_MAIN