test/regress: cover event_del() waiting mechanism

Since we have some issues (see refs) for changing waiting order in event_del()
I wrote this simple test, so maybe this test can explain something or at least
cover what we have before and show it will be broken.

P.S. we really need avoid such stuff like lets-test-with-sleep/usleep.

Refs: #225
Refs: #226
Refs: #236

test/regress.c

@@ -31,6 +31,10 @@
 #include <windows.h>
 #endif
 
+#ifdef EVENT__HAVE_PTHREADS
+#include <pthread.h>
+#endif
+
 #include "event2/event-config.h"
 
 #include <sys/types.h>
@@ -929,6 +933,67 @@ test_fork(void)
 	cleanup_test();
 }
 
+#ifdef EVENT__HAVE_PTHREADS
+static void* del_wait_thread(void *arg)
+{
+	struct timeval tv_start, tv_end;
+
+	evutil_gettimeofday(&tv_start, NULL);
+	event_dispatch();
+	evutil_gettimeofday(&tv_end, NULL);
+
+	test_timeval_diff_eq(&tv_start, &tv_end, 300);
+
+	end:
+	;
+}
+
+static void
+del_wait_cb(evutil_socket_t fd, short event, void *arg)
+{
+	struct timeval delay = { 0, 300*1000 };
+	TT_BLATHER(("Sleeping"));
+	evutil_usleep_(&delay);
+	test_ok = 1;
+}
+
+static void
+test_del_wait(void)
+{
+	struct event ev;
+	pthread_t thread;
+
+	setup_test("event_del will wait: ");
+
+	event_set(&ev, pair[1], EV_READ, del_wait_cb, &ev);
+	event_add(&ev, NULL);
+
+	pthread_create(&thread, NULL, del_wait_thread, NULL);
+
+	if (write(pair[0], TEST1, strlen(TEST1)+1) < 0) {
+		tt_fail_perror("write");
+	}
+
+	{
+		struct timeval delay = { 0, 30*1000 };
+		evutil_usleep_(&delay);
+	}
+
+	{
+		struct timeval tv_start, tv_end;
+		evutil_gettimeofday(&tv_start, NULL);
+		event_del(&ev);
+		evutil_gettimeofday(&tv_end, NULL);
+		test_timeval_diff_eq(&tv_start, &tv_end, 270);
+	}
+
+	pthread_join(thread, NULL);
+
+	end:
+	;
+}
+#endif
+
 static void
 signal_cb_sa(int sig)
 {
@@ -3301,6 +3366,11 @@ struct testcase_t main_testcases[] = {
 #ifndef _WIN32
 	LEGACY(fork, TT_ISOLATED),
 #endif
+#ifdef EVENT__HAVE_PTHREADS
+	/** TODO: support win32 */
+	LEGACY(del_wait, TT_ISOLATED|TT_NEED_THREADS),
+#endif
+
 	END_OF_TESTCASES
 };