FIFOScheduler: added automake wakeup

Sometimes, when the max thread count is exceeded, it is possible for
the scheduler to lock up. This is because the scheduler is only run when
a new job is put into the queue, and so it is possible for a job to be
blocked by thread limitations and be left sitting in the queue. If the
main program is waiting on this job to finish before scheduling a new one,
then the system deadlocks.

I added a second background thread to the scheduler that wakes the
scheduler up every 20us to resolve this and prevent these deadlocks.

1 files changed, 12 insertions, 1 deletions

diff --git a/include/framework/scheduling/FIFOScheduler.h b/include/framework/scheduling/FIFOScheduler.h
index 513a3a2..b77a8a1 100644
--- a/include/framework/scheduling/FIFOScheduler.h
+++ b/include/framework/scheduling/FIFOScheduler.h
@@ -10,7 +10,7 @@
 
 #include <thread>
 #include <condition_variable>
-
+#include <chrono>
 #include "framework/scheduling/Task.h"
 #include "framework/scheduling/statistics.h"
 
@@ -19,6 +19,8 @@
 
 namespace de {
 
+using namespace std::literals::chrono_literals;
+
 
 class FIFOScheduler {
 private:
@@ -33,6 +35,7 @@ public:
       , m_shutdown(false)
     {
         m_sched_thrd = std::thread(&FIFOScheduler::run, this);
+        m_sched_wakeup_thrd = std::thread(&FIFOScheduler::periodic_wakeup, this);
         m_thrd_pool.resize(m_thrd_cnt);
     }
 
@@ -77,6 +80,7 @@ private:
     std::condition_variable m_cv;
 
     std::thread m_sched_thrd;
+    std::thread m_sched_wakeup_thrd;
     ctpl::thread_pool m_thrd_pool;
 
     std::atomic<size_t> m_used_thrds;
@@ -84,6 +88,13 @@ private:
 
     SchedulerStatistics m_stats;
 
+    void periodic_wakeup() {
+        do {
+            std::this_thread::sleep_for(10us);
+            m_cv.notify_all();
+        } while (!m_shutdown.load());
+    }
+
     void schedule_next() {
         assert(m_task_queue.size() > 0);
         auto t = m_task_queue.pop();