[PATCH 2/3] PR remote/19496, interrupted syscall in forking-threads-plus-bkpt

[Don Breazeal <donb@codesourcery.com>]

This patch addresses "fork:Interrupted system call" (or wait:) failures
in gdb.threads/forking-threads-plus-breakpoint.exp.

The test program spawns ten threads, each of which do ten fork/waitpid
sequences.  The cause of the problem was that when one of the fork
children exited before the corresponding fork parent could initiate its
waitpid for that child, a SIGCHLD was delivered and interrupted a fork
or waitpid in another thread.

The fix was to wrap the system calls in a loop to retry the call if
it was interrupted, like:

do
  {
    pid = fork ();
  }
while (pid == -1 && errno == EINTR);

Since this is a Linux-only test I figure it is OK to use errno and EINTR.

Tested on Nios II Linux target with x86 Linux host.

Thanks,
--Don

gdb/testsuite/ChangeLog:
2016-01-27  Don Breazeal  <donb@codesourcery.com>

	PR remote/19496
	* gdb.threads/forking-threads-plus-breakpoint.c (thread_forks):
	Retry fork and waitpid on interrupted system call errors.

---
 .../gdb.threads/forking-threads-plus-breakpoint.c  |   14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/gdb/testsuite/gdb.threads/forking-threads-plus-breakpoint.c b/gdb/testsuite/gdb.threads/forking-threads-plus-breakpoint.c
index fc64d93..c169e18 100644
--- a/gdb/testsuite/gdb.threads/forking-threads-plus-breakpoint.c
+++ b/gdb/testsuite/gdb.threads/forking-threads-plus-breakpoint.c
@@ -22,6 +22,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <stdlib.h>
+#include <errno.h>
 
 /* Number of threads.  Each thread continuously spawns a fork and wait
    for it.  If we have another thread continuously start a step over,
@@ -49,14 +50,23 @@ thread_forks (void *arg)
     {
       pid_t pid;
 
-      pid = fork ();
+      do
+	{
+	  pid = fork ();
+	}
+      while (pid == -1 && errno == EINTR);
 
       if (pid > 0)
 	{
 	  int status;
 
 	  /* Parent.  */
-	  pid = waitpid (pid, &status, 0);
+	  do
+	    {
+	      pid = waitpid (pid, &status, 0);
+	    }
+	  while (pid == -1 && errno == EINTR);
+
 	  if (pid == -1)
 	    {
 	      perror ("wait");
-- 
1.7.0.4