[fpc-pascal] USB Human Interface Devices

[James Richters]

Thanks for figuring out the critical section needs to be initialized.  Stefan's example did not do this:
https://github.com/svpantazi/libusbxhid/blob/master/libusbhid_test_with_thread.pp

maybe it's something you can get away with on Linux...

I'll put in the init and done.   Should I enter critical section only for writing to shared variables, or also when reading them?

I'm also wondering if there is some way to tell if a thread is currently running or not... I don't want to try to start it again if it's already running.  I can make some flag that the threat sets when it starts and clears when it exits, but I am wondering if there already something in place to check to see if a thread exists.

James


-----Original Message-----
From: fpc-pascal <fpc-pascal-bounces at lists.freepascal.org> On Behalf Of Jean SUZINEAU
Sent: Wednesday, August 28, 2019 7:04 AM
To: fpc-pascal at lists.freepascal.org
Subject: Re: [fpc-pascal] USB Human Interface Devices

Hello,

It seems you didn't initialized you critical section using InitCriticalSection.
The documentation of EnterCriticalSection :
https://www.freepascal.org/docs-html/rtl/system/entercriticalsection.html
The one of InitCriticalSection:
https://www.freepascal.org/docs-html/rtl/system/initcriticalsection.html

At the end, you need to call DoneCriticalSection  to release the associated system resources ( https://www.freepascal.org/docs-html/rtl/system/donecriticalsection.html).

Note: these is related to freepascal implementation of critical sections, in windows API, the function names are slightly different, InitializeCriticalSection/EnterCriticalSection/DeleteCriticalSection
(https://docs.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-entercriticalsection)


Le 28/08/2019 à 01:50, James Richters a écrit :
> One thing I wasn't able to duplicate however was the use of      EnterCriticalsection(criticalSection);  and  LeaveCriticalsection(criticalSection);  when writing to shared variables.  If I try to ever use EnterCriticalsection(criticalSection); in the read thread, My program just instantly locks up and I can't even break out of it.    If I try to use it in the main program I instantly get
> EAccessViolation: Access violation
>    $00007FFF18A2DF23
>    $00007FFF189E9BBC
>    $00007FFF189E9AD0
>    $000000010000DCDA
>    $000000010000D54B
>    $000000010000218B  PROCESS_USB_DATA,  line 475 of WHB04B-4_test.pas
>    $0000000100002B37  SIMPLETERMINAL,  line 641 of WHB04B-4_test.pas
>    $0000000100002DDD  USE_MPG_DEVICE,  line 675 of WHB04B-4_test.pas
>    $0000000100002F93  main,  line 699 of WHB04B-4_test.pas
>    $0000000100002FE6
>    $0000000100011350
>    $0000000100001980
>    $00007FFF17B47E94
>    $00007FFF18A4A251
> Line 475 is    EnterCriticalsection(criticalSection);
> I left where I had the criticalsection stuff in the program but commented out.   It does seem to work fine without it though.. since the read, I am curious what I'm doing wrong, or if I need to do something else because I'm on Windows.

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