avoid deadlock when using compile cache with blocking executors

- avoid taking cache lock in compile task destructor
- avoid holding cache lock while posting compile task
- add unit test trying to provoke deadlock
- bonus: fix blocking executor implementation
  (did not work with threads <= task limit)

1 files changed, 1 insertions, 1 deletions

diff --git a/vespalib/src/vespa/vespalib/util/threadstackexecutorbase.cpp b/vespalib/src/vespa/vespalib/util/threadstackexecutorbase.cpp
index efb1dbf4054..ad5d78d5ab6 100644
--- a/vespalib/src/vespa/vespalib/util/threadstackexecutorbase.cpp
+++ b/vespalib/src/vespa/vespalib/util/threadstackexecutorbase.cpp
@@ -87,6 +87,7 @@ ThreadStackExecutorBase::obtainTask(Worker &worker)
         if (!worker.idle) {
             assert(_taskCount != 0);
             --_taskCount;
+            wakeup(monitor);
             _barrier.completeEvent(worker.task.token);
             worker.idle = true;
         }
@@ -96,7 +97,6 @@ ThreadStackExecutorBase::obtainTask(Worker &worker)
             worker.task = std::move(_tasks.front());
             worker.idle = false;
             _tasks.pop();
-            wakeup(monitor);
             return true;
         }
         if (_closed) {