Fix GH-18956: PHP-FPM Process Count Inconsistencies

This fixes extra increments on keep alive that happen for follow up
request in headers reading stage. It is because the accepting stage
is only done on the first request. It adds a new flag to the on_read
fastcgi callback that sets whether the kept alive request is being
done and then skips the further active increments.

It might still leave issues with incorrect decrement of the active
number of processes. This is done in accepting stage before incrementing
which might still be problematic if there are already some running
processes as it decrements their number first and result in incorrect
total (lower than the actual number).

Closes GH-19191

Author: bukka

main/fastcgi.c

@@ -201,7 +201,7 @@ typedef struct _fcgi_req_hook 	fcgi_req_hook;
 
 struct _fcgi_req_hook {
 	void(*on_accept)(void);
-	void(*on_read)(void);
+	void(*on_read)(bool keptAlive);
 	void(*on_close)(void);
 };
 
@@ -874,7 +874,11 @@ static void fcgi_hook_dummy(void) {
 	return;
 }
 
-fcgi_request *fcgi_init_request(int listen_socket, void(*on_accept)(void), void(*on_read)(void), void(*on_close)(void))
+static void fcgi_hook_dummy_bool(bool) {
+	return;
+}
+
+fcgi_request *fcgi_init_request(int listen_socket, void(*on_accept)(void), void(*on_read)(bool), void(*on_close)(void))
 {
 	fcgi_request *req = calloc(1, sizeof(fcgi_request));
 	req->listen_socket = listen_socket;
@@ -897,7 +901,7 @@ fcgi_request *fcgi_init_request(int listen_socket, void(*on_accept)(void), void(
 	*/
 	req->out_pos = req->out_buf;
 	req->hook.on_accept = on_accept ? on_accept : fcgi_hook_dummy;
-	req->hook.on_read = on_read ? on_read : fcgi_hook_dummy;
+	req->hook.on_read = on_read ? on_read : fcgi_hook_dummy_bool;
 	req->hook.on_close = on_close ? on_close : fcgi_hook_dummy;
 
 #ifdef _WIN32
@@ -1364,6 +1368,7 @@ int fcgi_accept_request(fcgi_request *req)
 	OVERLAPPED ov;
 #endif
 
+	bool keptAlive = false;
 	while (1) {
 		if (req->fd < 0) {
 			while (1) {
@@ -1372,6 +1377,7 @@ int fcgi_accept_request(fcgi_request *req)
 				}
 
 				req->hook.on_accept();
+				keptAlive = false;
 #ifdef _WIN32
 				if (!req->tcp) {
 					pipe = (HANDLE)_get_osfhandle(req->listen_socket);
@@ -1479,7 +1485,8 @@ int fcgi_accept_request(fcgi_request *req)
 		} else if (in_shutdown) {
 			return -1;
 		}
-		req->hook.on_read();
+		req->hook.on_read(keptAlive);
+		keptAlive = true;
 		int read_result = fcgi_read_request(req);
 		if (read_result == 1) {
 #ifdef _WIN32

main/fastcgi.h

@@ -91,7 +91,7 @@ void fcgi_close(fcgi_request *req, int force, int destroy);
 int fcgi_in_shutdown(void);
 void fcgi_terminate(void);
 int fcgi_listen(const char *path, int backlog);
-fcgi_request* fcgi_init_request(int listen_socket, void(*on_accept)(void), void(*on_read)(void), void(*on_close)(void));
+fcgi_request* fcgi_init_request(int listen_socket, void(*on_accept)(void), void(*on_read)(bool), void(*on_close)(void));
 void fcgi_destroy_request(fcgi_request *req);
 void fcgi_set_allowed_clients(char *ip);
 int fcgi_accept_request(fcgi_request *req);

sapi/fpm/fpm/fpm_request.c

@@ -58,7 +58,7 @@ void fpm_request_accepting(void)
 	fpm_scoreboard_update_commit(1, -1, 0, 0, 0, 0, 0, FPM_SCOREBOARD_ACTION_INC, NULL);
 }
 
-void fpm_request_reading_headers(void)
+void fpm_request_reading_headers(bool keptAlive)
 {
 	struct fpm_scoreboard_proc_s *proc;
 
@@ -98,8 +98,10 @@ void fpm_request_reading_headers(void)
 	proc->content_length = 0;
 	fpm_scoreboard_proc_release(proc);
 
-	/* idle--, active++, request++ */
-	fpm_scoreboard_update_commit(-1, 1, 0, 0, 1, 0, 0, FPM_SCOREBOARD_ACTION_INC, NULL);
+	if (!keptAlive) {
+		/* idle--, active++, request++ */
+		fpm_scoreboard_update_commit(-1, 1, 0, 0, 1, 0, 0, FPM_SCOREBOARD_ACTION_INC, NULL);
+	}
 }
 
 void fpm_request_info(void)

sapi/fpm/fpm/fpm_request.h

@@ -6,7 +6,7 @@
 /* hanging in accept() */
 void fpm_request_accepting(void);
 /* start reading fastcgi request from very first byte */
-void fpm_request_reading_headers(void);
+void fpm_request_reading_headers(bool keptAlive);
 /* not a stage really but a point in the php code, where all request params have become known to sapi */
 void fpm_request_info(void);
 /* the script is executing */