threads hung on read call with SMP configuration

[Mathieu <mat...@gm...>]

Hi,

When using the -t <threads_count> option, the created threads are
blocked after one cycle (the screen is not refreshed anymore, and no
more client is added).

However, entering anything on the keyboard unblock one thread, but
just for one cycle. Not using the -t option works as well.

The configuration used is the following:
- Hardware: HP server with 8cores intel CPU (not a virtual machine)
- OS: Debian Jessie
- Kernel: 3.16.0

Funnily enough, doing a strace on the main process group unblock the
situation (it seems attaching strace sends a signal to the process
that could cause this behaviour).

Nonetheless, making a strace on only one of the thread shows that it
is blocked on the read call (in screen.c), apparently ignoring the
VTIME timer.

Not sure if anyone encountered the same problem, but if so, below and
attached is a patch that fixes it (using select prior to read).

--
Mat

--- screen.c 2007-04-26 09:26:59.000000000 +0200
+++ /usr/src/curl-loader-0.56/screen.c 2015-05-31 10:44:41.712447334 +0200
@@ -82,6 +82,9 @@
   struct termios otty, ntty;
   int ch = -1;

+  struct timeval tv;
+  fd_set readset;
+
   tcgetattr(STDIN_FILENO, &otty);
   ntty = otty;

@@ -98,6 +101,10 @@
   ntty.c_cc[VMIN]  = 0;      /* non-block for input  */
   ntty.c_cc[VTIME] = 1;      /* with timer*/

+  tv.tv_sec = 0;
+  tv.tv_usec = 100000;
+
+
 #if 0
 /*
  * use this to flush the input buffer before
@@ -115,15 +122,21 @@

   if (!tcsetattr(STDIN_FILENO, FLAG, &ntty))
    {
+     FD_ZERO(&readset);
+     FD_SET(STDIN_FILENO, &readset);
+     select(STDIN_FILENO + 1, &readset, NULL, NULL, &tv);
      /* get a single character from stdin */
-     if (read (STDIN_FILENO, &ch, 1 ) == -1)
-       {
-         if (!stop_loading)
-           {
-             fprintf(stderr, "%s - read() failed with errno %d.\n",
-                     __func__, errno);
-           }
-         return -1;
+     if (FD_ISSET(fileno(stdin), &readset))
+      {
+        if (read (STDIN_FILENO, &ch, 1 ) == -1)
+          {
+            if (!stop_loading)
+              {
+                fprintf(stderr, "%s - read() failed with errno %d.\n",
+                        __func__, errno);
+              }
+            return -1;
+          }
        }

      /* restore old settings */