core: fix parallel_for data race

modules/core/src/parallel_impl.cpp

@@ -190,7 +190,7 @@ class WorkerThread
 {
 public:
     ThreadPool& thread_pool;
-    unsigned id;
+    const unsigned id;
     pthread_t posix_thread;
     bool is_created;
 
@@ -418,14 +418,15 @@ void WorkerThread::thread_body()
         stat.threadWake = getTickCount();
 #endif
 
+        CV_LOG_VERBOSE(NULL, 5, "Thread: checking for new job");
+        if (CV_WORKER_ACTIVE_WAIT_THREADS_LIMIT == 0)
+            allow_active_wait = true;
+        Ptr<ParallelJob> j_ptr; swap(j_ptr, job);
+        has_wake_signal = false;    // TODO .store(false, std::memory_order_release)
+        pthread_mutex_unlock(&mutex);
+
         if (!stop_thread)
         {
-            CV_LOG_VERBOSE(NULL, 5, "Thread: checking for new job");
-            if (CV_WORKER_ACTIVE_WAIT_THREADS_LIMIT == 0)
-                allow_active_wait = true;
-            Ptr<ParallelJob> j_ptr; swap(j_ptr, job);
-            has_wake_signal = false;
-            pthread_mutex_unlock(&mutex);
             ParallelJob* j = j_ptr;
             if (j)
             {
@@ -480,10 +481,6 @@ void WorkerThread::thread_body()
                 }
             }
         }
-        else
-        {
-            pthread_mutex_unlock(&mutex);
-        }
 #ifdef CV_PROFILE_THREADS
         stat.threadFree = getTickCount();
         stat.keepActive = allow_active_wait;
@@ -595,40 +592,42 @@ void ThreadPool::run(const Range& range, const ParallelLoopBody& body, double ns
             CV_LOG_VERBOSE(NULL, 5, "MainThread: wake worker threads...");
             for (size_t i = 0; i < threads.size(); ++i)
             {
+                WorkerThread& thread = *(threads[i].get());
+                if (
 #if !defined(CV_USE_GLOBAL_WORKERS_COND_VAR)
-                bool isActive = threads[i]->isActive;
-                if (isActive || threads[i]->has_wake_signal)
-#else
-                if (threads[i]->has_wake_signal)
+                        thread.isActive ||
 #endif
+                        thread.has_wake_signal
+                        || !thread.job.empty()  // #10881
+                )
                 {
-                    pthread_mutex_lock(&threads[i]->mutex);
-                    threads[i]->job = job;
+                    pthread_mutex_lock(&thread.mutex);
+                    thread.job = job;
 #if !defined(CV_USE_GLOBAL_WORKERS_COND_VAR)
-                    isActive = threads[i]->isActive;
+                    bool isActive = thread.isActive;
 #endif
-                    threads[i]->has_wake_signal = true;
+                    thread.has_wake_signal = true;
 #ifdef CV_PROFILE_THREADS
                     threads_stat[i + 1].reset();
 #endif
-                    pthread_mutex_unlock(&threads[i]->mutex);
+                    pthread_mutex_unlock(&thread.mutex);
 #if !defined(CV_USE_GLOBAL_WORKERS_COND_VAR)
                     if (!isActive)
                     {
-                        pthread_cond_broadcast/*pthread_cond_signal*/(&threads[i]->cond_thread_wake); // wake thread
+                        pthread_cond_broadcast/*pthread_cond_signal*/(&thread.cond_thread_wake); // wake thread
                     }
 #endif
                 }
                 else
                 {
-                    CV_Assert(threads[i]->job.empty());
-                    threads[i]->job = job;
-                    threads[i]->has_wake_signal = true;
+                    CV_Assert(thread.job.empty());
+                    thread.job = job;
+                    thread.has_wake_signal = true;
 #ifdef CV_PROFILE_THREADS
                     threads_stat[i + 1].reset();
 #endif
 #if !defined(CV_USE_GLOBAL_WORKERS_COND_VAR)
-                    pthread_cond_broadcast/*pthread_cond_signal*/(&threads[i]->cond_thread_wake); // wake thread
+                    pthread_cond_broadcast/*pthread_cond_signal*/(&thread.cond_thread_wake); // wake thread
 #endif
                 }
             }