add non-stop test that stresses thread starvation issues

This commit adds a non-stop mode test originally inspired by
signal-while-stepping-over-bp-other-thread.exp, that exposes the
thread starvation issues fixed by the previous patches.  It sets a set
of threads stepping in parallel, and has one of them get a signal.
Without the previous fixes, this would fail with timeouts.

gdb/testsuite/
2015-01-09  Pedro Alves  <palves@redhat.com>

	* gdb.threads/non-stop-fair-events.c: New file.
	* gdb.threads/non-stop-fair-events.exp: New file.

3 files changed, 250 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index aa1e22b..d3dacf1 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2015-01-09  Pedro Alves  <palves@redhat.com>
 
+	* gdb.threads/non-stop-fair-events.c: New file.
+	* gdb.threads/non-stop-fair-events.exp: New file.
+
+2015-01-09  Pedro Alves  <palves@redhat.com>
+
 	* gdb.base/annota1.exp (thread_test): Use srcfile and binfile from
 	the global scope.  Set a breakpoint after all threads are started
 	rather than stepping over two source lines.  Expect the prompt.
diff --git a/gdb/testsuite/gdb.threads/non-stop-fair-events.c b/gdb/testsuite/gdb.threads/non-stop-fair-events.c
new file mode 100644
index 0000000..6a9d31d
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/non-stop-fair-events.c
@@ -0,0 +1,84 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2014-2015 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <pthread.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <signal.h>
+
+#define NUM_THREADS 10
+const int num_threads = NUM_THREADS;
+
+pthread_t child_thread[NUM_THREADS];
+volatile pthread_t signal_thread;
+volatile int got_sig;
+
+void
+handler (int signo)
+{
+  got_sig = 1;
+}
+
+void
+loop_broke (void)
+{
+}
+
+#define INF_LOOP				\
+  do						\
+    {						\
+      while (!got_sig)				\
+	;					\
+    }						\
+  while (0)
+
+void *
+child_function (void *arg)
+{
+  pthread_t self = pthread_self ();
+
+  while (1)
+    {
+      INF_LOOP; /* set thread breakpoint here */
+      loop_broke ();
+    }
+}
+
+int
+main (void)
+{
+  int res;
+  int i;
+
+  alarm (60);
+
+  signal (SIGUSR1, handler);
+
+  for (i = 0; i < NUM_THREADS; i++)
+    {
+      res = pthread_create (&child_thread[i], NULL, child_function, NULL);
+    }
+
+  while (1)
+    {
+      pthread_kill (signal_thread, SIGUSR1); /* set kill breakpoint here */
+      INF_LOOP;
+      loop_broke ();
+    }
+
+  exit(EXIT_SUCCESS);
+}
diff --git a/gdb/testsuite/gdb.threads/non-stop-fair-events.exp b/gdb/testsuite/gdb.threads/non-stop-fair-events.exp
new file mode 100644
index 0000000..9b7b9ca
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/non-stop-fair-events.exp
@@ -0,0 +1,161 @@
+# Copyright (C) 2014-2015 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test that GDB in non-stop mode gives roughly equal priority to
+# events of all threads.
+
+standard_testfile
+set executable ${testfile}
+
+if [target_info exists gdb,nosignals] {
+    verbose "Skipping ${testfile}.exp because of nosignals."
+    return -1
+}
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug pthreads}] == -1} {
+    return -1
+}
+
+gdb_test_no_output "set non-stop on"
+
+if ![runto_main] {
+    return -1
+}
+
+# We want "handle print", to make sure the target backend reports the
+# signal to the run control core.
+gdb_test "handle SIGUSR1 print nostop pass" ""
+
+# Get current value of VAR from the inferior.  TEST is used as test
+# message.
+
+proc get_value {var test} {
+    global expect_out
+    global gdb_prompt
+    global decimal
+
+    set value -1
+    gdb_test_multiple "print $var" "$test" {
+	-re ".*= ($decimal).*\r\n$gdb_prompt $" {
+	    set value $expect_out(1,string)
+	    pass "$test"
+        }
+    }
+    return ${value}
+}
+
+set NUM_THREADS [get_value "num_threads" "get num_threads"]
+
+# Account for the main thread.
+incr NUM_THREADS
+
+# Run threads to their start positions.  This prepares for a new test
+# sequence.
+
+proc restart {} {
+    global gdb_prompt
+    global NUM_THREADS
+
+    delete_breakpoints
+
+    gdb_test "print got_sig = 0" " = 0"
+
+    gdb_breakpoint [gdb_get_line_number "set thread breakpoint here"]
+    gdb_breakpoint [gdb_get_line_number "set kill breakpoint here"]
+
+    set test "continue -a&"
+    gdb_test_multiple $test $test {
+	-re "Continuing.\r\n$gdb_prompt " {
+	    pass $test
+	}
+    }
+
+    for {set i 1} { $i <= $NUM_THREADS } { incr i } {
+	set test "thread $i restarted"
+	gdb_test_multiple "" $test {
+	    -re "breakpoint here" {
+		# The prompt was already matched in the "continue &"
+		# test above.  We're now consuming asynchronous output
+		# that comes after the prompt.
+		pass $test
+	    }
+	}
+    }
+
+    delete_breakpoints
+}
+
+# The test proper.  SIGNAL_THREAD is the thread that has been elected
+# to receive the SIGUSR1 signal.
+
+proc test {signal_thread} {
+    global gdb_prompt
+    global NUM_THREADS
+
+    with_test_prefix "signal_thread=$signal_thread" {
+	restart
+
+	# Set all threads stepping the infinite loop line in parallel.
+	for {set i 2} { $i <= $NUM_THREADS } { incr i } {
+	    gdb_test "thread $i" \
+		"child_function.*set thread breakpoint here.*" \
+		"switch to thread $i to step it"
+
+	    if {$i == $signal_thread} {
+		gdb_test "print signal_thread = self" " = .*"
+	    }
+
+	    gdb_test "step&" "" "set $i thread stepping"
+	}
+
+	gdb_test "thread 1" "Switching to .*" \
+	    "switch to the main thread to queue signal"
+
+	# Let the main thread queue the signal.
+	gdb_breakpoint "loop_broke"
+	set test "continue &"
+	gdb_test_multiple $test $test {
+	    -re "Continuing.\r\n$gdb_prompt " {
+		pass $test
+	    }
+	}
+
+	# Wait for all threads to finish their steps, and for the main
+	# thread to hit the breakpoint.
+	for {set i 1} { $i <= $NUM_THREADS } { incr i } {
+	    set test "thread $i broke out of loop"
+	    gdb_test_multiple "" $test {
+		-re "loop_broke" {
+		    # The prompt was already matched in the "continue
+		    # &" test above.  We're now consuming asynchronous
+		    # output that comes after the prompt.
+		    pass $test
+		}
+	    }
+	}
+
+	# It's helpful to have this in the log if the test ever
+	# happens to fail.
+	gdb_test "info threads"
+    }
+}
+
+# The kernel/debug API may always walk its thread list looking for the
+# first with an event, resulting in giving priority to e.g. the thread
+# with lowest kernel thread ID.  So test once with the signal pending
+# in each thread, except the main thread.
+for {set i 2} { $i <= $NUM_THREADS } { incr i } {
+    test $i
+}