Improve fix for phpGH-16889

The original patch[1] cared only about pipe handles in the rset, but
would be problematic if there are other handles (e.g. files in the
rset, or pipes/files in the other sets), because `php_select()` would
return immediately, reporting all non read-pipe handles as ready, but
possibly never reporting read-pipe handles.

We fix this by applying different logic for the case where only pipe
handles are supplied in the rset, but no handles in the wset or eset.
In this case `php_select()` only returns when actually one of the
handles is ready, or when the timeout expires.  To avoid busy looping
in this case, we sleep for a short amount of time.  This matches POSIX
behavior.

In all other cases, `php_select()` behaves as before (i.e. prior to the
original fix), that is it returns immediately, reporting all handles as
ready.

We also add a test case that demonstrates multiplexing the output of a
couple of child processes.

See also the discussion on <php#16917>.

[1] <php@b614b4a>

Author: cmb69

ext/standard/tests/general_functions/proc_open_multiplex.phpt

@@ -0,0 +1,37 @@
+--TEST--
+Multiplexing of child output
+--FILE--
+<?php
+$php = getenv("TEST_PHP_EXECUTABLE");
+$desc = [
+    ["null"],
+    ["pipe", "w"],
+    ["null"]
+];
+$read_pipes = [];
+for ($i = 0; $i < 10; $i++) {
+    $procs[] = proc_open([$php, "-r", "usleep(100000 * (10 - $i)); echo 'hello$i';"], $desc, $pipes);
+    $read_pipes[] = $pipes[1];
+}
+$rset = $read_pipes;
+$wset = null;
+$eset = null;
+while (!empty($read_pipes) && stream_select($rset, $wset, $eset, 2) > 0) {
+    foreach ($rset as $pipe) {
+        echo fread($pipe, 6), "\n";
+        unset($read_pipes[array_search($pipe, $read_pipes)]);
+    }
+    $rset = $read_pipes;
+}
+?>
+--EXPECT--
+hello9
+hello8
+hello7
+hello6
+hello5
+hello4
+hello3
+hello2
+hello1
+hello0

win32/select.c

@@ -16,12 +16,15 @@
 
 #include "php.h"
 #include "php_network.h"
+#include "win32/time.h"
 
 /* Win32 select() will only work with sockets, so we roll our own implementation here.
  * - If you supply only sockets, this simply passes through to winsock select().
  * - If you supply file handles, there is no way to distinguish between
  *   ready for read/write or OOB, so any set in which the handle is found will
- *   be marked as ready. Pipes will be checked if they are ready for read, though.
+ *   be marked as ready.
+ * - If you supply only pipe handles in rfds, and no handles in wfds or efds,
+ *   the pipes will only be marked as ready if there is data available.
  * - If you supply a mixture of handles and sockets, the system will interleave
  *   calls between select() and WaitForMultipleObjects(). The time slicing may
  *   cause this function call to take up to 100 ms longer than you specified.
@@ -34,6 +37,7 @@ PHPAPI int php_select(php_socket_t max_fd, fd_set *rfds, fd_set *wfds, fd_set *e
 	HANDLE handles[MAXIMUM_WAIT_OBJECTS];
 	int handle_slot_to_fd[MAXIMUM_WAIT_OBJECTS];
 	int n_handles = 0, i;
+	int num_read_pipes = 0;
 	fd_set sock_read, sock_write, sock_except;
 	fd_set aread, awrite, aexcept;
 	int sock_max_fd = -1;
@@ -78,6 +82,9 @@ PHPAPI int php_select(php_socket_t max_fd, fd_set *rfds, fd_set *wfds, fd_set *e
 					sock_max_fd = i;
 				}
 			} else {
+				if (SAFE_FD_ISSET(i, rfds) && GetFileType(handles[n_handles]) == FILE_TYPE_PIPE) {
+					num_read_pipes++;
+				}
 				handle_slot_to_fd[n_handles] = i;
 				n_handles++;
 			}
@@ -136,7 +143,7 @@ PHPAPI int php_select(php_socket_t max_fd, fd_set *rfds, fd_set *wfds, fd_set *e
 					if (WAIT_OBJECT_0 == WaitForSingleObject(handles[i], 0)) {
 						if (SAFE_FD_ISSET(handle_slot_to_fd[i], rfds)) {
 							DWORD avail_read = 0;
-							if (GetFileType(handles[i]) != FILE_TYPE_PIPE
+							if (num_read_pipes < n_handles
 								|| !PeekNamedPipe(handles[i], NULL, 0, NULL, &avail_read, NULL)
 								|| avail_read > 0
 							) {
@@ -156,6 +163,9 @@ PHPAPI int php_select(php_socket_t max_fd, fd_set *rfds, fd_set *wfds, fd_set *e
 				}
 			}
 		}
+		if (retcode == 0 && num_read_pipes == n_handles && sock_max_fd < 0) {
+			usleep(100);
+		}
 	} while (retcode == 0 && (ms_total == INFINITE || GetTickCount64() < limit));
 
 	if (rfds) {