I have had an issue with my 2024r2.1 desktop application that has the main thread hanging randomly while all the threads still work just fine. (Linux desktop app main thread frozen, other threads still executing) With the large changes around threading in 2024r3.1 I thought I would give it a go to see it if fixed my issue.
While I didn’t initially need to change my program to use preemptive threads, I did want to play around with them. For part of one of my apps, I am trying to get consistent cycle times for processing math calculations at a regular interval. I built a test console app to compare event loop (DoEvents), timer, co-op and preemptive threads with both normal (5) and high priority (50).
My first issue is that using Thread.Sleep(10) in a preemptive thread caused the program to crash.
libc++abi: terminating due to uncaught exception of type std::__1::system_error: mutex lock failed: Invalid argument
[1] 54023 abort
I did see some reports about Thread.Sleep in preemptive threads so I left it there and continued on without sleeping the preemptive threads. This brought some even more weird behaviour.
First test was in the debugger, I noticed that preemptive threads cause Thread.Sleep and DoEvents to finish early most of the time.
This is in microseconds, target was 10,000us.
| Iteration | Event Loop | Timer | Coop Thread | Hi-Pri Coop Thread | Preemptive Thread | Hi-Pri Preemptive Thread |
|---|---|---|---|---|---|---|
| 1 | 86.875 | 15624.042 | 4.875 | 4.583 | 0.208 | 97.792 |
| 2 | 372.292 | 12379.875 | 10081.875 | 22.042 | 0.250 | 0.250 |
| 3 | 108.958 | 15890.000 | 10652.500 | 50.333 | 0.208 | 0.250 |
| 4 | 9284.000 | 12791.750 | 37.167 | 2.667 | 0.250 | 207.583 |
| 5 | 8478.833 | 14810.125 | 110.750 | 17.167 | 0.250 | 46.917 |
| 6 | 140.542 | 12501.750 | 37.042 | 4.292 | 0.208 | 0.250 |
| 7 | 939.167 | 15985.333 | 10.875 | 42.958 | 0.250 | 0.208 |
| 8 | 137.333 | 13139.958 | 32.083 | 10380.542 | 0.250 | 0.208 |
| 9 | 35.042 | 15047.500 | 48.750 | 10075.500 | 0.250 | 288.167 |
| 10 | 162.375 | 13453.500 | 39.583 | 24.500 | 0.250 | 350.958 |
I then ran it as a built app and the behaviour changed, now the co-op threads are fairly consistent, however, DoEvents(10) finished early every time.
| Iteration | Event Loop | Timer | Coop Thread | Hi-Pri Coop Thread | Preemptive Thread | Hi-Pri Preemptive Thread |
|---|---|---|---|---|---|---|
| 1 | 19.083 | 10956.958 | 10598.625 | 10603.708 | 0.042 | 0.042 |
| 2 | 17.458 | 20549.667 | 10358.125 | 10355.750 | 0.042 | 0.000 |
| 3 | 12.458 | 10580.667 | 9434.208 | 9427.167 | 0.000 | 0.042 |
| 4 | 12.167 | 20084.833 | 11508.583 | 11320.125 | 0.000 | 0.042 |
| 5 | 19.708 | 10801.708 | 10656.292 | 10825.667 | 0.042 | 0.042 |
| 6 | 13.083 | 20842.125 | 11321.375 | 11315.708 | 0.042 | 0.042 |
| 7 | 12.417 | 12486.833 | 11277.250 | 11255.292 | 0.042 | 0.042 |
| 8 | 12.000 | 19754.875 | 9956.875 | 9955.083 | 0.042 | 0.042 |
| 9 | 11.708 | 10749.292 | 9502.125 | 9500.208 | 0.042 | 0.000 |
| 10 | 11.625 | 20827.083 | 10174.792 | 10175.833 | 0.042 | 0.042 |
This is all kinda weird and I haven’t dug in enough as I have been battling my hanging issue. Am I doing something wrong here or is this behaviour that anyone else has been observing? Please see my test app attached (I can cause the crash by uncommenting sender.Sleep(10) in a preemptive thread)