Don't freeze with unreadable processes

Don't freeze if an exiting process can't be read from. (Bug#19860).
This fixes a bug I introduced in
2014-07-08T07:24:07Z@eggert@cs.ucla.edu
"* process.c: Add sanity checks for file descriptors."
Dmitry Gutov did most of the legwork in finding the problem.
* src/process.c (wait_reading_process_output):
Treat non-running processes that can't be read from
the same as other non-running processes.

1 files changed, 22 insertions, 18 deletions

diff --git a/src/process.c b/src/process.c
index c7455072962..3e04cb76387 100644
--- a/src/process.c
+++ b/src/process.c
@@ -4785,37 +4785,41 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
       if (wait_proc && wait_proc->raw_status_new)
         update_status (wait_proc);
       if (wait_proc
-          && wait_proc->infd >= 0
           && ! EQ (wait_proc->status, Qrun)
           && ! EQ (wait_proc->status, Qconnect))
         {
           bool read_some_bytes = false;
 
           clear_waiting_for_input ();
-          XSETPROCESS (proc, wait_proc);
 
-          /* Read data from the process, until we exhaust it.  */
-          while (true)
+          /* If data can be read from the process, do so until exhausted.  */
+          if (wait_proc->infd >= 0)
             {
-              int nread = read_process_output (proc, wait_proc->infd);
-              if (nread < 0)
+              XSETPROCESS (proc, wait_proc);
+
+              while (true)
                 {
-                  if (errno == EIO || errno == EAGAIN)
-                    break;
+                  int nread = read_process_output (proc, wait_proc->infd);
+                  if (nread < 0)
+                    {
+                    if (errno == EIO || errno == EAGAIN)
+                      break;
 #ifdef EWOULDBLOCK
-                  if (errno == EWOULDBLOCK)
-                    break;
+                    if (errno == EWOULDBLOCK)
+                      break;
 #endif
-                }
-              else
-                {
-                  if (got_some_input < nread)
-                    got_some_input = nread;
-                  if (nread == 0)
-                    break;
-                  read_some_bytes = true;
+                    }
+                  else
+                    {
+                      if (got_some_input < nread)
+                        got_some_input = nread;
+                      if (nread == 0)
+                        break;
+                      read_some_bytes = true;
+                    }
                 }
             }
+
           if (read_some_bytes && do_display)
             redisplay_preserve_echo_area (10);