#multi-thread

Linux code to decode Ogg Vorbis files with multi-thread support sourceforge.net/projects/jamailmar

This release fixes some bugs in multi-threading support, and introduces a new feature. Now, RF Compare automatically generates SVG graphics for each compared reference vs. predicted structure pair:

PyTorch의 DataLoader 내부에서 OpenCV를 사용할 때, multi-thread 문제로 인해 deadlock이 발생할 수 있는 듯 하다.

Differences between Locks, Mutexes, and Semaphores

  James writes to me:

I’m having trouble finding concrete definitions for Locks, Mutexes, and Semaphores

What I do know is:

Semaphores keep track of how many processes have gained access (“P”) to a resource and block (suspend and send to priority queue) processes once it’s maxed out. They have no concept of ownership and anyone can call unlock (“V”)

Binary semaphores are the same as above except…

In the program I am working on right now, I have a Qt GUI that display some relevant information. From time to time, the background thread is supposed to compute the information and update the display, such as the status bar and OpenGL viewer. At some point last week I added this functionality.

Since then I  started to run into some extremely random segmentation fault. It took me quite a while to track down the reasons. 

It turns out to be the update from the other non-GUI thread. For some reason it will crash the whole program. I am still looking into deeper causes, but for now, I just use a signal/slot to send the job back to the main GUI to update. It seems to work fine.

UPDATE: When specifying the connection betwen signals and slots, we need to specify the Qt connection type to avoid data hazard, although it's relatively rare.

connect(src, SIGNAL(signal-signature), dest, SLOT(slot-signature), Qt::QueuedConnection);

UPDATE 2: If you encounter something similar to the error below, probably you have this Qt dynamic dequeue issue.

[xcb] Unknown request in queue while dequeuing. [xcb] Most likely this is a multi-threaded client and XInitThreads has not been called. [xcb] Aborting, sorry about that. a.out: ../../src/xcb_io.c:179: dequeue_pending_request: Assertion `!xcb_xlib_unknown_req_in_deq' failed. Aborted (core dumped)

More info:

http://qt-project.org/doc/qt-4.8/threads-qobject.html

http://stackoverflow.com/questions/18109037/controlling-paintgl-method-how-to-decide-what-to-paint

http://stackoverflow.com/questions/2072735/emit-qt-signal-from-non-qt-thread-or-ouside-qt-main-event-loop-with-at-4-5

     Camille folded her arms over one another and hesitantly walked back and forth as the two of them waited for Magnus -- how exactly was she supposed to explain this..? Of course, Magnus knew Camille wasn't the most faithful immortal there was out there -- but to be dating another while the two were in a passionate relationship, and take that one seriously as well? It wasn't...cheating -- no, it was simply pleasing another. But things had changed and Camille was really beginning to feel for Rock -- it was...peculiar. "Magnus should be here any moment." She murmured before flashing Rock a slightly nervous smile. Ah, great...