Allow `process-contact' not to block

* doc/lispref/processes.texi (Process Information): Document it.

* lisp/simple.el (list-processes--refresh): Don't wait for contact
information for non-setup processes.

* src/process.c (Fprocess_contact): Take an optional parameter to
avoid blocking (bug#37408).

1 files changed, 15 insertions, 5 deletions

diff --git a/src/process.c b/src/process.c
index 372277a953d..a95192d8fba 100644
--- a/src/process.c
+++ b/src/process.c
@@ -1456,7 +1456,7 @@ DEFUN ("process-query-on-exit-flag",
 }
 
 DEFUN ("process-contact", Fprocess_contact, Sprocess_contact,
-       1, 2, 0,
+       1, 3, 0,
        doc: /* Return the contact info of PROCESS; t for a real child.
 For a network or serial or pipe connection, the value depends on the
 optional KEY arg.  If KEY is nil, value is a cons cell of the form
@@ -1465,9 +1465,12 @@ connection; it is t for a pipe connection.  If KEY is t, the complete
 contact information for the connection is returned, else the specific
 value for the keyword KEY is returned.  See `make-network-process',
 `make-serial-process', or `make-pipe-process' for the list of keywords.
+
 If PROCESS is a non-blocking network process that hasn't been fully
-set up yet, this function will block until socket setup has completed.  */)
-  (Lisp_Object process, Lisp_Object key)
+set up yet, this function will block until socket setup has completed.
+If the optional NO-BLOCK parameter is specified, return nil instead of
+waiting for the process to be fully set up.*/)
+  (Lisp_Object process, Lisp_Object key, Lisp_Object no_block)
 {
   Lisp_Object contact;
 
@@ -1476,8 +1479,15 @@ set up yet, this function will block until socket setup has completed.  */)
 
 #ifdef DATAGRAM_SOCKETS
 
-  if (NETCONN_P (process))
-    wait_for_socket_fds (process, "process-contact");
+  if (NETCONN_P (process) && XPROCESS (process)->infd < 0)
+    {
+      /* Usually wait for the network process to finish being set
+       * up. */
+      if (!NILP (no_block))
+        return Qnil;
+
+      wait_for_socket_fds (process, "process-contact");
+    }
 
   if (DATAGRAM_CONN_P (process)
       && (EQ (key, Qt) || EQ (key, QCremote)))