TaskSystem: Fix early shutdown

... conceptually, it was possible that a previous task
decrements the `num_threads_running_` counter before it is
incremented by the next task. Therefore, we have to unify
the queue and thread status in a single counter
(`total_workload_`) and ensure that woken threads increment
it before decrementing it for popping a queue.

1 files changed, 1 insertions, 2 deletions

diff --git a/src/buildtool/multithreading/task_system.hpp b/src/buildtool/multithreading/task_system.hpp
index 20950142..6387988a 100644
--- a/src/buildtool/multithreading/task_system.hpp
+++ b/src/buildtool/multithreading/task_system.hpp
@@ -54,8 +54,7 @@ class TaskSystem {
     std::vector<std::thread> threads_{};
     std::vector<NotificationQueue> queues_{};
     std::atomic<std::size_t> index_{0};
-    WaitableOneWayFlag queues_read_{};
-    WaitableZeroCounter num_threads_running_{};
+    WaitableZeroCounter total_workload_{};
 
     static constexpr std::size_t kNumberOfAttempts = 5;