Event loop: what is due called when waiting fails; units on Windows

looponce() called nothing due when waiting for the sockets failed,
returning at once: a caller waiting for a timer turned forever. What is
due is called all the same, and on Windows WSAEINTR is no failure, not
errno. looptest reports any failure to wait with its error; fibertest
starts Winsock, its loop could not be made without, and recurses into
half of a fiber's stack rather than most of it, which Windows takes
more of. The units case shows what a test which never finished wrote.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/loop.c

@@ -660,7 +660,13 @@ int looponce(struct loop *l, int maxwait){
 			if(l->pfds[j].revents) readyadd(l, l->pios[j], l->pfds[j].revents);
 	}
 #endif
-	if(n < 0 && errno != EINTR) return -1;
+	/* failing, what is due is still called: the caller decides whether to
+	   go on */
+#ifdef _WIN32
+	if(n < 0 && WSAGetLastError() == WSAEINTR) n = 0;
+#else
+	if(n < 0 && errno == EINTR) n = 0;
+#endif
 	l->now = l->clock();
 	if(woken){
 		wakedrain(l);
@@ -671,7 +677,7 @@ int looponce(struct loop *l, int maxwait){
 
 		if(io) io->func(l, io, l->readyev[i]);
 	}
-	n = l->nready;
+	if(n >= 0) n = l->nready;
 	l->nready = 0;
 	timersturn(l);
 	timersfire(l);

tests/cases/units.py

@@ -18,8 +18,10 @@ def run(t):
             try:
                 done = subprocess.run([path, seed], stdout=subprocess.PIPE,
                                       stderr=subprocess.STDOUT, timeout=120)
-            except subprocess.TimeoutExpired:
-                t.fail(f"{unit} {seed} finishes")
+            except subprocess.TimeoutExpired as exc:
+                out = (exc.output or b"").decode(errors="replace")
+                t.fail(f"{unit} {seed} finishes",
+                       actual="last: " + (out.splitlines() or ["nothing"])[-1])
                 continue
             out = done.stdout.decode(errors="replace")
             for line in out.splitlines():

tests/fibertest.c

@@ -234,7 +234,7 @@ static unsigned deepresult;
 
 static void deeper(void *arg){
 	fiberyield();
-	deepresult = deep(150);
+	deepresult = deep(100);
 }
 
 static void depth(void){
@@ -243,7 +243,7 @@ static void depth(void){
 	if(fiberinit(&f, STACK)) return;
 	fiberstart(&f, deeper, NULL);
 	while(fiberresume(&f));
-	check(deepresult == deep(150), "a fiber uses most of its stack", "wrong result");
+	check(deepresult == deep(100), "a fiber uses half of its stack", "wrong result");
 	fiberfree(&f);
 }
 
@@ -283,7 +283,10 @@ static void onloop(void){
 	int i, left, early = 0;
 	char what[64];
 
-	if(loopinit(&l)) return;
+	if(loopinit(&l)){
+		check(0, "fibers sleep on the loop's timers", "loopinit() failed");
+		return;
+	}
 	for(i = 0; i < NWAIT; i++){
 		memset(w + i, 0, sizeof(w[i]));
 		if(fiberinit(&w[i].f, STACK)) return;
@@ -306,6 +309,11 @@ static void onloop(void){
 }
 
 int main(int argc, char **argv){
+#ifdef _WIN32
+	WSADATA wd;
+
+	WSAStartup(MAKEWORD(2, 2), &wd);
+#endif
 	if(!fiberusable()){
 		printf("ok fibers cannot be used here (a shadow stack): each client has a thread\n");
 		return 0;

tests/looptest.c

@@ -12,7 +12,22 @@
 #include "../src/proxy.h"
 #include "../src/loop.h"
 
-static int failures;
+static int failures, waitfails, lasterr;
+
+/* looponce(), a failure to wait counted, with its error */
+static int turn(struct loop *l, int maxwait){
+	int n = looponce(l, maxwait);
+
+	if(n < 0){
+		waitfails++;
+#ifdef _WIN32
+		lasterr = WSAGetLastError();
+#else
+		lasterr = errno;
+#endif
+	}
+	return n;
+}
 
 static void check(int cond, const char *label, const char *what){
 	if(cond) printf("ok %s\n", label);
@@ -134,7 +149,7 @@ static void timertest(void){
 		/* steps of a few ms to a second, and now and then a long stall */
 		if(rand_upto(500) == 0) fakenow += 1 + rand_upto(300000);
 		else fakenow += 1 + rand_upto(rand_upto(4) ? 1500 : 20);
-		looponce(&l, 0);
+		turn(&l, 0);
 		steps++;
 	}
 	pending = 0;
@@ -231,25 +246,25 @@ static void iotest(void){
 	a.io.func = iocall;
 	check(!loopadd(&l, &a.io), "sockets: a socket is added", "loopadd() failed");
 
-	looponce(&l, 100);
+	turn(&l, 100);
 	check(a.calls == 0, "sockets: nothing to read, no call", "called");
 
 	send(s2, "x", 1, 0);
-	for(i = 0; i < 10 && !a.calls; i++) looponce(&l, 200);
+	for(i = 0; i < 10 && !a.calls; i++) turn(&l, 200);
 	check(a.calls >= 1 && (a.revents & POLLIN), "sockets: what comes is readable", "no POLLIN");
 	recv(s1, buf, sizeof(buf), 0);
 
 	a.calls = 0;
 	a.revents = 0;
 	loopmod(&l, &a.io, POLLOUT);
-	for(i = 0; i < 10 && !a.calls; i++) looponce(&l, 200);
+	for(i = 0; i < 10 && !a.calls; i++) turn(&l, 200);
 	check(a.calls >= 1 && (a.revents & POLLOUT) && !(a.revents & POLLIN),
 	      "sockets: waited for writing, writable", "no POLLOUT");
 
 	loopmod(&l, &a.io, 0);
 	a.calls = 0;
 	send(s2, "y", 1, 0);
-	looponce(&l, 200);
+	turn(&l, 200);
 	check(a.calls == 0, "sockets: waited for nothing, not called", "called");
 
 	/* both ready: whichever is called first deletes the other */
@@ -262,7 +277,7 @@ static void iotest(void){
 	c.other = &a;
 	send(s4, "z", 1, 0);
 	a.calls = c.calls = 0;
-	for(i = 0; i < 10 && a.calls + c.calls == 0; i++) looponce(&l, 200);
+	for(i = 0; i < 10 && a.calls + c.calls == 0; i++) turn(&l, 200);
 	check(a.calls + c.calls == 1, "sockets: one deleted in this turn is not called", "both called");
 
 	/* the one deleted can be added again; the far side closing it is
@@ -275,7 +290,7 @@ static void iotest(void){
 	a.calls = 0;
 	a.revents = 0;
 	closesock(s2);
-	for(i = 0; i < 10 && !a.calls; i++) looponce(&l, 200);
+	for(i = 0; i < 10 && !a.calls; i++) turn(&l, 200);
 	check(a.calls >= 1 && (a.revents & (POLLIN | POLLHUP)) && recv(s1, buf, sizeof(buf), 0) == 0,
 	      "sockets: the far side closing is readable", "not reported");
 
@@ -349,7 +364,7 @@ static void realtest(void){
 	t.func = realfire;
 	start = looptime();
 	looptimerset(&tl, &t, start + 150);
-	while(!timerfired) looponce(&tl, -1);
+	while(!timerfired) turn(&tl, -1);
 	took = looptime() - start;
 	sprintf(what, "fired after %u ms", (unsigned)took);
 	check(took >= 150 && took < 1100, "real time: a timer fires when it is due", what);
@@ -357,7 +372,7 @@ static void realtest(void){
 	start = looptime();
 	if(startposter()) check(0, "real time: a thread is started", "failed");
 	else {
-		looponce(&tl, 5000);
+		turn(&tl, 5000);
 		took = looptime() - start;
 		sprintf(what, "after %u ms", (unsigned)took);
 		check(posted && took < 2000, "real time: a message from another thread wakes the loop", what);
@@ -386,5 +401,11 @@ int main(int argc, char **argv){
 	timertest();
 	iotest();
 	realtest();
+	{
+		char what[64];
+
+		sprintf(what, "%d failed, the last with error %d", waitfails, lasterr);
+		check(!waitfails, "waiting for sockets never fails", what);
+	}
 	return failures;
 }