Fix #33107: cycles fixed threads 1 was still having two cores do work,

because main thread works as well.

2 files changed, 12 insertions, 3 deletions

diff --git a/intern/cycles/util/util_task.cpp b/intern/cycles/util/util_task.cpp
index ea0abd6f54f..8c4ec312256 100644
--- a/intern/cycles/util/util_task.cpp
+++ b/intern/cycles/util/util_task.cpp
@@ -168,10 +168,16 @@ void TaskScheduler::init(int num_threads)
 	if(users == 0) {
 		do_exit = false;
 
-		/* launch threads that will be waiting for work */
-		if(num_threads == 0)
+		if(num_threads == 0) {
+			/* automatic number of threads will be main thread + num cores */
 			num_threads = system_cpu_thread_count();
+		}
+		else {
+			/* main thread will also work, for fixed threads we count it too */
+			num_threads -= 1;
+		}
 
+		/* launch threads that will be waiting for work */
 		threads.resize(num_threads);
 		thread_level.resize(num_threads);
 
diff --git a/intern/cycles/util/util_task.h b/intern/cycles/util/util_task.h
index a2f284479c7..b795ca7524b 100644
--- a/intern/cycles/util/util_task.h
+++ b/intern/cycles/util/util_task.h
@@ -94,7 +94,10 @@ public:
 	static void init(int num_threads = 0);
 	static void exit();
 
-	static int num_threads() { return threads.size(); }
+	/* number of threads that can work on tasks, main thread counts too */
+	static int num_threads() { return threads.size() + 1; }
+
+	/* test if any session is using the scheduler */
 	static bool active() { return users != 0; }
 
 protected: