[PATCH] [gdb/testsuite] Fix timeout in gdb.base/bg-execution-repeat.exp

[Tom de Vries]

I ran into the following test failure with test-case
gdb.base/bg-execution-repeat.exp:
...
(gdb) PASS: gdb.base/bg-execution-repeat.exp: c&: repeat bg command
^M
Breakpoint 2, foo () at bg-execution-repeat.c:23^M
23        return 0; /* set break here */^M
print 1^M
$1 = 1^M
(gdb) PASS: gdb.base/bg-execution-repeat.exp: c&: input still accepted
FAIL: gdb.base/bg-execution-repeat.exp: c&: breakpoint hit 2 (timeout)
...

The failure can be easily reproduced by adding a sleep 5 here:
...
+    sleep 5
     gdb_test "print 1" " = 1" "input still accepted"
...

There's a race in the test-case, between:
- the command handled in the foreground: the "print 1" command, and
- the command handled in the background: the continue command.

The current way of dealing with this is by putting the inferior to sleep for 5
seconds:
...
  foo ();
  sleep (5);
  foo ();
...
with the aim that the "print 1" command will win the race.

This method is both slow and unreliable.

Fix this by making the inferior wait just long enough for the "print 1"
command to win the race.

This reduces running time from ~11s to ~1s.

Tested on aarch64-linux.

PR testsuite/31794
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31794
---
 gdb/testsuite/gdb.base/bg-execution-repeat.c   | 16 +++++++++++++++-
 gdb/testsuite/gdb.base/bg-execution-repeat.exp |  3 +++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.base/bg-execution-repeat.c b/gdb/testsuite/gdb.base/bg-execution-repeat.c
index 2caa7d442f6..c92d34ed9f9 100644
--- a/gdb/testsuite/gdb.base/bg-execution-repeat.c
+++ b/gdb/testsuite/gdb.base/bg-execution-repeat.c
@@ -23,11 +23,25 @@ foo (void)
   return 0; /* set break here */
 }
 
+static volatile int do_wait;
+
+static void
+wait (void)
+{
+  while (do_wait)
+    usleep (10 * 1000);
+}
+
 int
 main (void)
 {
   foo ();
-  sleep (5);
+
+  do_wait = 1;
+  wait ();
+  /* do_wait set to 0 externally.  */
+
   foo ();
+
   return 0;
 }
diff --git a/gdb/testsuite/gdb.base/bg-execution-repeat.exp b/gdb/testsuite/gdb.base/bg-execution-repeat.exp
index a4cc7daa702..3497ef2d47d 100644
--- a/gdb/testsuite/gdb.base/bg-execution-repeat.exp
+++ b/gdb/testsuite/gdb.base/bg-execution-repeat.exp
@@ -68,6 +68,9 @@ proc test {continue_cmd} {
     # stopped.
     gdb_test "print 1" " = 1" "input still accepted"
 
+    # Allow the breakpoint to trigger.
+    gdb_test -no-prompt-anchor "set var do_wait=0"
+
     # Make sure we see a stop after the print, and not before.  Don't
     # expect a prompt, as we had resumed the inferior in the background.
     set test "breakpoint hit 2"

base-commit: 2597ca3417d9adb0adda135c90ab86c4ea675139
-- 
2.35.3