Fix data race (tsan) bug

2 files changed, 15 insertions, 12 deletions

diff --git a/build2/scheduler.cxx b/build2/scheduler.cxx
index cd621bc..e6a0bc6 100644
--- a/build2/scheduler.cxx
+++ b/build2/scheduler.cxx
@@ -186,8 +186,8 @@ namespace build2
     try { shutdown (); } catch (system_error&) {}
   }
 
-  void scheduler::
-  wait_idle ()
+  auto scheduler::
+  wait_idle () -> lock
   {
     lock l (mutex_);
 
@@ -200,6 +200,8 @@ namespace build2
       this_thread::yield ();
       l.lock ();
     }
+
+    return l;
   }
 
   size_t scheduler::
@@ -319,7 +321,7 @@ namespace build2
     // The scheduler must not be active though some threads might still be
     // comming off from finishing a task. So we busy-wait for them.
     //
-    wait_idle ();
+    lock l (wait_idle ());
 
     max_active_ = max_active;
   }
@@ -411,7 +413,7 @@ namespace build2
     // comming off from finishing a task and trying to report progress. So we
     // busy-wait for them (also in ~monitor_guard()).
     //
-    wait_idle ();
+    lock l (wait_idle ());
 
     monitor_count_ = &c;
     monitor_tshold_.store (t, memory_order_relaxed);
diff --git a/build2/scheduler.hxx b/build2/scheduler.hxx
index 20e5128..4880392 100644
--- a/build2/scheduler.hxx
+++ b/build2/scheduler.hxx
@@ -256,7 +256,7 @@ namespace build2
       {
         if (s_ != nullptr)
         {
-          s_->wait_idle (); // See monitor() for details.
+          lock l (s_->wait_idle ()); // See monitor() for details.
           s_->monitor_count_ = nullptr;
           s_->monitor_func_  = nullptr;
         }
@@ -300,12 +300,6 @@ namespace build2
       task_queue_ = nullptr;
     }
 
-    // Assuming all the task have been executed, busy-wait for all the threads
-    // to become idle. Normally you don't need to call this function directly.
-    //
-    void
-    wait_idle ();
-
     // Return the number of hardware threads or 0 if unable to determine.
     //
     static size_t
@@ -324,9 +318,16 @@ namespace build2
     size_t
     shard_size (size_t mul = 1, size_t div = 1) const;
 
-  private:
+    // Assuming all the task have been executed, busy-wait for all the threads
+    // to become idle. Return the lock over the scheduler mutex. Normally you
+    // don't need to call this function directly.
+    //
     using lock = std::unique_lock<std::mutex>;
 
+    lock
+    wait_idle ();
+
+  private:
     void
     activate_helper (lock&);