Revert the fix for GH-11498

People relied on manually waiting for children, but the fix for GH-11498
broke this. Fixing this in PHP is fundamentally incompatible with doing
the wait loop in userland. This reverts to the old behaviour.

Closes GH-11863.

Author: nielsdos

NEWS

@@ -34,6 +34,10 @@ PHP                                                                        NEWS
   . Avoid adding an unnecessary read-lock when loading script from shm if
     restart is in progress. (mikhainin)
 
+- PCNTL:
+  . Revert behaviour of receiving SIGCHLD signals back to the behaviour
+    before 8.1.22. (nielsdos)
+
 - Standard:
   . Prevent int overflow on $decimals in number_format. (Marc Bennewitz)
 

ext/pcntl/pcntl.c

@@ -1338,68 +1338,26 @@ static void pcntl_signal_handler(int signo, siginfo_t *siginfo, void *context)
 static void pcntl_signal_handler(int signo)
 #endif
 {
-	struct php_pcntl_pending_signal *psig_first = PCNTL_G(spares);
-	if (!psig_first) {
+	struct php_pcntl_pending_signal *psig = PCNTL_G(spares);
+	if (!psig) {
 		/* oops, too many signals for us to track, so we'll forget about this one */
 		return;
 	}
+	PCNTL_G(spares) = psig->next;
 
-	struct php_pcntl_pending_signal *psig = NULL;
-
-	/* Standard signals may be merged into a single one.
-	 * POSIX specifies that SIGCHLD has the si_pid field (https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/signal.h.html),
-	 * so we'll handle the merging for that signal.
-	 * See also: https://www.gnu.org/software/libc/manual/html_node/Merged-Signals.html */
-	if (signo == SIGCHLD) {
-		/* Note: The first waitpid result is not necessarily the pid that was passed above!
-		 *       We therefore cannot avoid the first waitpid() call. */
-		int status;
-		pid_t pid;
-		while (true) {
-			do {
-				errno = 0;
-				/* Although Linux specifies that WNOHANG will never result in EINTR, POSIX doesn't say so:
-				 * https://pubs.opengroup.org/onlinepubs/9699919799/functions/waitpid.html */
-				pid = waitpid(-1, &status, WNOHANG | WUNTRACED);
-			} while (pid <= 0 && errno == EINTR);
-			if (pid <= 0) {
-				if (UNEXPECTED(!psig)) {
-					/* The child might've been consumed by another thread and will be handled there. */
-					return;
-				}
-				break;
-			}
-
-			psig = psig ? psig->next : psig_first;
-			psig->signo = signo;
-
-#ifdef HAVE_STRUCT_SIGINFO_T
-			psig->siginfo = *siginfo;
-			psig->siginfo.si_pid = pid;
-#endif
-
-			if (UNEXPECTED(!psig->next)) {
-				break;
-			}
-		}
-	} else {
-		psig = psig_first;
-		psig->signo = signo;
+	psig->signo = signo;
+	psig->next = NULL;
 
 #ifdef HAVE_STRUCT_SIGINFO_T
-		psig->siginfo = *siginfo;
+	psig->siginfo = *siginfo;
 #endif
-	}
-
-	PCNTL_G(spares) = psig->next;
-	psig->next = NULL;
 
 	/* the head check is important, as the tick handler cannot atomically clear both
 	 * the head and tail */
 	if (PCNTL_G(head) && PCNTL_G(tail)) {
-		PCNTL_G(tail)->next = psig_first;
+		PCNTL_G(tail)->next = psig;
 	} else {
-		PCNTL_G(head) = psig_first;
+		PCNTL_G(head) = psig;
 	}
 	PCNTL_G(tail) = psig;
 	PCNTL_G(pending_signals) = 1;

ext/pcntl/tests/gh11498.phpt renamed to ext/pcntl/tests/waiting_on_sigchild_pcntl_wait.phpt

@@ -1,5 +1,5 @@
 --TEST--
-GH-11498 (SIGCHLD is not always returned from proc_open)
+Waiting on SIGCHLD with a pcntl_wait() loop
 --EXTENSIONS--
 pcntl
 --SKIPIF--
@@ -14,8 +14,10 @@ $processes = [];
 
 pcntl_async_signals(true);
 pcntl_signal(SIGCHLD, function($sig, $info) use (&$processes) {
-    echo "SIGCHLD\n";
-    unset($processes[$info['pid']]);
+    while (($pid = pcntl_wait($status, WUNTRACED | WNOHANG)) > 0) {
+        echo "SIGCHLD\n";
+        unset($processes[$pid]);
+    }
 }, false);
 
 for ($i = 0; $i <= 5; $i++) {