MINOR: config: add a new tune.idle-pool.shared global setting.

Enables ('on') or disables ('off') sharing of idle connection pools between
threads for a same server. The default is to share them between threads in
order to minimize the number of persistent connections to a server, and to
optimize the connection reuse rate. But to help with debugging or when
suspecting a bug in HAProxy around connection reuse, it can be convenient to
forcefully disable this idle pool sharing between multiple threads, and force
this option to "off". The default is on.

This could have been nice to have during the idle connections debugging,
but it's not too late to add it!

doc/configuration.txt

@@ -682,6 +682,7 @@ The following keywords are supported in the "global" section :
    - tune.http.cookielen
    - tune.http.logurilen
    - tune.http.maxhdr
+   - tune.idle-pool.shared
    - tune.idletimer
    - tune.lua.forced-yield
    - tune.lua.maxmem
@@ -1949,6 +1950,15 @@ tune.http.maxhdr <number>
   1..32767. Keep in mind that each new header consumes 32bits of memory for
   each session, so don't push this limit too high.
 
+tune.idle-pool.shared { on | off }
+  Enables ('on') or disables ('off') sharing of idle connection pools between
+  threads for a same server. The default is to share them between threads in
+  order to minimize the number of persistent connections to a server, and to
+  optimize the connection reuse rate. But to help with debugging or when
+  suspecting a bug in HAProxy around connection reuse, it can be convenient to
+  forcefully disable this idle pool sharing between multiple threads, and force
+  this option to "off". The default is on.
+
 tune.idletimer <timeout>
   Sets the duration after which haproxy will consider that an empty buffer is
   probably associated with an idle stream. This is used to optimally adjust

include/haproxy/global-t.h

@@ -68,6 +68,7 @@
 #define GTUNE_INSECURE_SETUID    (1<<17)
 #define GTUNE_FD_ET              (1<<18)
 #define GTUNE_SCHED_LOW_LATENCY  (1<<19)
+#define GTUNE_IDLE_POOL_SHARED   (1<<20)
 
 /* SSL server verify mode */
 enum {

src/backend.c

@@ -1107,6 +1107,10 @@ static struct connection *conn_backend_get(struct server *srv, int is_safe)
 	if (conn)
 		goto done;
 
+	/* pool sharing globally disabled ? */
+	if (!(global.tune.options & GTUNE_IDLE_POOL_SHARED))
+		goto done;
+
 	/* Are we allowed to pick from another thread ? We'll still try
 	 * it if we're running low on FDs as we don't want to create
 	 * extra conns in this case, otherwise we can give up if we have

src/haproxy.c

@@ -1788,6 +1788,9 @@ static void init(int argc, char **argv)
 #if defined(SO_REUSEPORT)
 	global.tune.options |= GTUNE_USE_REUSEPORT;
 #endif
+#ifdef USE_THREAD
+	global.tune.options |= GTUNE_IDLE_POOL_SHARED;
+#endif
 
 	pid = getpid();
 	progname = *argv;

src/server.c

@@ -5333,6 +5333,25 @@ remove:
 	return task;
 }
 
+/* config parser for global "tune.idle-pool.shared", accepts "on" or "off" */
+static int cfg_parse_idle_pool_shared(char **args, int section_type, struct proxy *curpx,
+                                      struct proxy *defpx, const char *file, int line,
+                                      char **err)
+{
+	if (too_many_args(1, args, err, NULL))
+		return -1;
+
+	if (strcmp(args[1], "on") == 0)
+		global.tune.options |= GTUNE_IDLE_POOL_SHARED;
+	else if (strcmp(args[1], "off") == 0)
+		global.tune.options &= ~GTUNE_IDLE_POOL_SHARED;
+	else {
+		memprintf(err, "'%s' expects either 'on' or 'off' but got '%s'.", args[0], args[1]);
+		return -1;
+	}
+	return 0;
+}
+
 /* config parser for global "tune.pool-{low,high}-fd-ratio" */
 static int cfg_parse_pool_fd_ratio(char **args, int section_type, struct proxy *curpx,
                                    struct proxy *defpx, const char *file, int line,
@@ -5360,6 +5379,7 @@ static int cfg_parse_pool_fd_ratio(char **args, int section_type, struct proxy *
 
 /* config keyword parsers */
 static struct cfg_kw_list cfg_kws = {ILH, {
+	{ CFG_GLOBAL, "tune.idle-pool.shared",       cfg_parse_idle_pool_shared },
 	{ CFG_GLOBAL, "tune.pool-high-fd-ratio",     cfg_parse_pool_fd_ratio },
 	{ CFG_GLOBAL, "tune.pool-low-fd-ratio",      cfg_parse_pool_fd_ratio },
 	{ 0, NULL, NULL }