[gnome-keyring] test-gkd-ssh-agent-service: Avoid race condition with server thread

[Daiki Ueno <dueno src gnome org>]

commit 91bc9368ca2eedef0dec3f5aa81f641ced07a9b6
Author: Simon McVittie <smcv debian org>
Date:   Sat Mar 9 17:56:55 2019 +0000

    test-gkd-ssh-agent-service: Avoid race condition with server thread
    
    These tests create a server thread in setup() and join it in teardown(),
    but there are various race conditions between them that can cause the
    test to hang. These are particularly reproducible when building on a
    single-CPU machine or VM, and particularly in the startup_shutdown
    test (which doesn't do anything, so it runs teardown() immediately
    after setup()).
    
    It's possible to get this preemption pattern:
    
         ___ Main thread ___                ___ Server thread ___
         g_thread_new()                     (starts)
         g_cond_wait() (blocks)
                                            ...
                                            g_cond_signal()
                                            (gets preempted here)
         exit setup()
         enter teardown()
         g_main_loop_quit()
                                            g_main_loop_run()
    
    which means g_main_loop_run() will never terminate, because it wasn't
    running yet when the main thread told the GMainLoop to quit, and the
    main thread won't tell it to quit again.
    
    One way to solve this would be for the server thread to signal
    test->cond from an idle callback instead of directly from
    server_thread(), to guarantee that the GMainLoop is already running.
    However, it seems easier to reason about if we avoid GMainLoop and
    iterate the main context directly.
    
    Signed-off-by: Simon McVittie <smcv debian org>
    Bug-Debian: https://bugs.debian.org/909416

 daemon/ssh-agent/test-gkd-ssh-agent-service.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)
---
diff --git a/daemon/ssh-agent/test-gkd-ssh-agent-service.c b/daemon/ssh-agent/test-gkd-ssh-agent-service.c
index 9a9ead99..5c7a6179 100644
--- a/daemon/ssh-agent/test-gkd-ssh-agent-service.c
+++ b/daemon/ssh-agent/test-gkd-ssh-agent-service.c
@@ -38,7 +38,8 @@ typedef struct {
        EggBuffer req;
        EggBuffer resp;
        GkdSshAgentService *service;
-       GMainLoop *loop;
+       GMainContext *server_thread_context;
+       volatile gint server_thread_stop;
        GSocketConnection *connection;
        GThread *thread;
        GMutex lock;
@@ -49,13 +50,9 @@ static gpointer
 server_thread (gpointer data)
 {
        Test *test = data;
-       GMainContext *context;
        gboolean ret;
 
-       context = g_main_context_new ();
-       test->loop = g_main_loop_new (context, FALSE);
-
-       g_main_context_push_thread_default (context);
+       g_main_context_push_thread_default (test->server_thread_context);
 
        ret = gkd_ssh_agent_service_start (test->service);
        g_assert_true (ret);
@@ -64,12 +61,10 @@ server_thread (gpointer data)
        g_cond_signal (&test->cond);
        g_mutex_unlock (&test->lock);
 
-       g_main_loop_run (test->loop);
+       while (g_atomic_int_get (&test->server_thread_stop) == 0)
+               g_main_context_iteration (test->server_thread_context, TRUE);
 
-       g_main_context_pop_thread_default (context);
-
-       g_main_context_unref (context);
-       g_main_loop_unref (test->loop);
+       g_main_context_pop_thread_default (test->server_thread_context);
 
        return NULL;
 }
@@ -139,6 +134,7 @@ setup (Test *test, gconstpointer unused)
 
        g_mutex_init (&test->lock);
        g_cond_init (&test->cond);
+       test->server_thread_context = g_main_context_new ();
 
        test->thread = g_thread_new ("ssh-agent", server_thread, test);
 
@@ -151,9 +147,12 @@ setup (Test *test, gconstpointer unused)
 static void
 teardown (Test *test, gconstpointer unused)
 {
-       g_main_loop_quit (test->loop);
+       g_atomic_int_set (&test->server_thread_stop, 1);
+       g_main_context_wakeup (test->server_thread_context);
        g_thread_join (test->thread);
 
+       g_main_context_unref (test->server_thread_context);
+
        g_clear_object (&test->connection);
 
        gkd_ssh_agent_service_stop (test->service);