fix allocating thread pool workers

Tasks are removed from the queue before a worker starts working
on it, which means that maTasks.size() is not the number of tasks
to do, because the worked on tasks are not included there.
This means the code could spawn only a smaller number of workers
than were needed (and than CPU cores that are available).

Change-Id: Ic6e6a79316cf48d82f2b80be7ad477b723b2c4e5
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/103955
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/include/comphelper/threadpool.hxx b/include/comphelper/threadpool.hxx
index 1cb9441cfdd1..f51daf4f70a4 100644
--- a/include/comphelper/threadpool.hxx
+++ b/include/comphelper/threadpool.hxx
@@ -72,7 +72,7 @@ public:
     void        joinAll();
 
     /// return the number of live worker threads
-    sal_Int32   getWorkerCount() const { return mnWorkers; }
+    sal_Int32   getWorkerCount() const { return mnMaxWorkers; }
 
     /// wait until all work is completed, then join all threads
     void        shutdown();
@@ -90,12 +90,15 @@ private:
     */
     std::unique_ptr<ThreadTask> popWorkLocked( std::unique_lock< std::mutex > & rGuard, bool bWait );
     void shutdownLocked(std::unique_lock<std::mutex>&);
+    void incBusyWorker();
+    void decBusyWorker();
 
     /// signalled when all in-progress tasks are complete
     std::mutex              maMutex;
     std::condition_variable maTasksChanged;
     bool                    mbTerminate;
-    std::size_t const       mnWorkers;
+    std::size_t const       mnMaxWorkers;
+    std::size_t             mnBusyWorkers;
     std::vector< std::unique_ptr<ThreadTask> >   maTasks;
     std::vector< rtl::Reference< ThreadWorker > > maWorkers;
 };