COCOS2DX Center Thread Priority

COCOS2DX Thread Priority problem

Whether it's iOS or Android, the time-consuming tasks have to be threaded, otherwise the program will not be able to prompt users for feedback. In the game if a lap cycle can not be completed in the 1/framerate (frame rate is 30 1/30) seconds, there will be dropped frames, game lag. For example, in the game to parse an animation JSON configuration, need 60ms, this if in the main thread to drop the frame, then another thread to parse the JSON, the parsing is finished and then notify the main thread? This is possible, but consider an extreme case where the thread switches to the JSON parsing thread until the JSON parsing is complete before switching to the main thread, which is not the same as dropping frames! so the ideal situation is to let the JSON parsing thread priority lower than the main thread, JSON parsing when the main thread is idle, which is the priority of the control threads, can I set the thread priority in COCOS2DX? Please see below.

1. Create threading Mode：

The creation thread takes the thread library in c++11, but the thread in c++11 does not specify a method for threading priority or CPU affinity (affinity) (such as Sched_setaffinity, Setthreadaffinitymask, Pthread_attr_setschedpolicy). It is possible to control thread priority by using a function in the Pthread library (currently using Pthread_setschedparam).

2. Thread Priority:

Sched_other, Sched_fifo, SCHED_RR, and other Sched_batch, Sched_batch and sched_idle are commonly used in the scheduling strategy of the middle thread priority of Unix-like systems. Refer to Sched_setscheduler (2)-Linux man page.

Sched_other: The newly created thread is this dispatch by default , and the main thread is this scheduling mode, which has no thread priority, and is fairly dispatched by the operating system when all threads are Sched_other-Dispatch mode.

Sched_fifo and SCHED_RR: There are priority schedules , high priority threads, and operating systems running high-priority threads. When both Sched_other and Sched_fifo (or SCHED_RR) are available,Sched_fifo (or SCHED_RR) always runs before Sched_other .

The difference between Sched_fifo and SCHED_RR is that, if the thread priority is the same, the Sched_fifo runs in the FIFO order, and the incoming thread waits until the previous thread finishes running or discards the CPU to execute. The SCHED_RR will rotate the time slice, the time slice is up, switch the execution thread.

The advantage of Sched_other is that the CPU utilization is higher than sched_fifo and SCHED_RR without the real-time (high priority thread switching thread) switch on the processing thread.

You can refer to the Linux process scheduling method (SCHED_OTHER,SCHED_FIFO,SCHED_RR)

3. Conclusion:

　　If the default scheduling rule of the main thread is not changed sched_other, the thread priority is set through pthread_setschedparm without effect, that is, there is no guarantee that other threads will not affect the execution efficiency of the main thread. If you change the schedule rule of the main thread to Sched_fifo (or SCHED_RR), the created thread also sets the schedule rule to Sched_fifo and sets the low priority, which guarantees a higher CPU usage for the main thread.

Add the following code in the appdelegate::applicationdidfinishlaunching change the main thread scheduling mode, the game can run normally, side effects are not found.

4. test Data

The maximum minimum value of the thread priority priority for a print is 47 to 15, not the legendary 1 to 99. Sched_other Max is a, Min is 15. Sched_fifo Max is a, Min is 15. SCHED_RR Max is a, Min is 15. Each test opens 2 threads (thread 1 and Thread 2), sets the scheduling mode and priority respectively, and the Scarlet Letter is a confusing place.

Mac Simulator

	Dispatch mode	Priority level	Log Print Count
Thread 1	Sched_other	46	16374
Thread 2	Sched_other	16	311
Thread 1	Sched_other	16	579
Thread 2	Sched_other	46	7856
Thread 1	Sched_other	30	1400
Thread 2	Sched_other	31	8082
Thread 1	Sched_other	31	8628
Thread 2	Sched_other	30	1864
Thread 1	Sched_rr	16	1099
Thread 2	Sched_other	46	12784

iOS simulator under Mac

	Dispatch mode	Priority level	Log Print Count
Thread 1	Sched_other	46	16799
Thread 2	Sched_other	16	238
Thread 1	Sched_other	16	3982
Thread 2	Sched_other	46	103177
Thread 1	Sched_other	30	2147
Thread 2	Sched_other	31	21478
Thread 1	Sched_rr	16	1674
Thread 2	Sched_other	46	16096

iphone 5s:

	Dispatch mode	Priority level	Log Print Count
Thread 1	Sched_other	46	463/1465/1553
Thread 2	Sched_other	16	1781/1726/1568
Thread 1	Sched_other	16	1030
Thread 2	Sched_other	46	1284
Thread 1	Sched_other	30	372
Thread 2	Sched_other	31	2005
Thread 1	Sched_rr	16	52262
Thread 2	Sched_other	46	1161
Thread 1	Sched_rr	46	13055
Thread 2	Sched_rr	16	1145
Thread 1	Sched_rr	46	19858
Thread 2	Sched_rr	45	2046

Under Mac App

	Dispatch mode	Priority level	Log Print Count
Thread 1	Sched_other	46	13099
Thread 2	Sched_other	16	59311
Thread 1	Sched_other	16	45864
Thread 2	Sched_other	46	3598
Thread 1	Sched_other	30	7512
Thread 2	Sched_other	31	4561
Thread 1	Sched_rr	16	57981
Thread 2	Sched_other	46	5909
Thread 1	Sched_rr	46	58960
Thread 2	Sched_rr	45	5494

Test the code for Mac app:

COCOS2DX Test Code:

COCOS2DX Center Thread Priority