From c9d651896970fced145f6b8c875200db01116a22 Mon Sep 17 00:00:00 2001
From: Stef Walter <stefw@gnome.org>
Date: Sun, 10 Nov 2013 00:16:28 +0100
Subject: [PATCH] gthreadpool: Cleanup thread pool unused threads

This requires different phases getting involved:
 * early: Signal all the unused pool threads, and change unused
   limits to zero, so no new unused pool threads.
 * default: Join all unused pool threads.
 * late: Free up the unused thread queue

https://bugzilla.gnome.org/show_bug.cgi?id=711744
---
 glib/gthreadpool.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/glib/gthreadpool.c b/glib/gthreadpool.c
index a122d8de9..b11a3bfd1 100644
--- a/glib/gthreadpool.c
+++ b/glib/gthreadpool.c
@@ -30,6 +30,7 @@
 
 #include "gasyncqueue.h"
 #include "gasyncqueueprivate.h"
+#include "gcleanup.h"
 #include "gmain.h"
 #include "gtestutils.h"
 #include "gtimer.h"
@@ -137,6 +138,20 @@ g_thread_pool_queue_push_unlocked (GRealThreadPool *pool,
     g_async_queue_push_unlocked (pool->queue, data);
 }
 
+static void
+ref_and_join_thread (GThread *thread)
+{
+  /*
+   * This is called as a cleanup function, but removed before the thread
+   * is destroyed. So we know the thread is valid here.
+   *
+   * g_thread_join() unrefs, so we need to first ref the thread, in order
+   * to avoid use/after free elsewhere.
+   */
+  g_thread_ref (thread);
+  g_thread_join (thread);
+}
+
 static GRealThreadPool*
 g_thread_pool_wait_for_new_pool (void)
 {
@@ -146,6 +161,7 @@ g_thread_pool_wait_for_new_pool (void)
   gint local_max_idle_time;
   gint last_wakeup_thread_serial;
   gboolean have_relayed_thread_marker = FALSE;
+  gpointer cleanup;
 
   local_max_unused_threads = g_atomic_int_get (&max_unused_threads);
   local_max_idle_time = g_atomic_int_get (&max_idle_time);
@@ -153,6 +169,14 @@ g_thread_pool_wait_for_new_pool (void)
 
   g_atomic_int_inc (&unused_threads);
 
+  /*
+   * While in the unused thread queue, this thread will need cleanup.
+   * Cleaned up again below.
+   */
+
+  cleanup = g_cleanup_push (G_CLEANUP_SCOPE, G_CLEANUP_PHASE_DEFAULT,
+                            (GCleanupFunc)ref_and_join_thread, g_thread_self ());
+
   do
     {
       if (g_atomic_int_get (&unused_threads) >= local_max_unused_threads)
@@ -221,6 +245,8 @@ g_thread_pool_wait_for_new_pool (void)
     }
   while (pool == wakeup_thread_marker);
 
+  g_cleanup_remove (cleanup);
+
   g_atomic_int_add (&unused_threads, -1);
 
   return pool;
@@ -422,6 +448,12 @@ g_thread_pool_start_thread (GRealThreadPool  *pool,
   return TRUE;
 }
 
+static void
+stop_all_unused_threads (void)
+{
+  g_thread_pool_set_max_unused_threads (0);
+}
+
 /**
  * g_thread_pool_new:
  * @func: a function to execute in the threads of the new thread pool
@@ -488,7 +520,22 @@ g_thread_pool_new (GFunc      func,
 
   G_LOCK (init);
   if (!unused_thread_queue)
+    {
       unused_thread_queue = g_async_queue_new ();
+
+      /* First stop having unused threads in early phase */
+      G_CLEANUP_FUNC_IN (stop_all_unused_threads, G_CLEANUP_PHASE_EARLY);
+
+      /*
+       * Next any still outstanding unused threads get g_thread_join()'d during
+       * G_CLEANUP_PHASE_DEFAULT. See g_thread_pool_wait_for_new_pool().
+       *
+       * Lastly at the very end destroy the unused_thread_queue. We can do this
+       * very late, as it owns all its own mutexes and doesn't have an item_free_func
+       * callback.
+       */
+      G_CLEANUP_IN (unused_thread_queue, g_async_queue_unref, G_CLEANUP_PHASE_GRAVEYARD);
+    }
   G_UNLOCK (init);
 
   if (retval->pool.exclusive)