Synchronizing between TThreads
lazarus / 64-FPC development

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ArminLinder · 2023-07-14 16:44

Hi folks,

I have been using Synchronize to sync TThread instances with the
program main thread a while. Is there a similar mechanism to
synchronize two arbitrary threads?

Thnx, Armin.

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Remy Lebeau · 2023-07-14 18:09

Simply use a suitable synchronization object, such as
TCriticalSection, TMutex, TMultiReadExclusiveWriteSynchronizer, etc
(depending on your needs) to protect the code/resources you want to
synchronize access to.

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Lulu · 2023-07-19 12:40

Hi, there is also RTLEvent. See in the folder where is installed
Lazarus, subfolder examples/multithreading there is a demo
waitforexample1.lpi

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marcov · 2023-07-19 12:46

I put message objects in a thread safe queue (tthreadlist or tlist
protected by criticalsection), and let the thread block on an TEvent.

If I put objects in the queue, I .Setevent the Tevent, and the thread
drains the queue. If it is empty, it resets the tevent and blocks on
it again.

This is fine for not too finegrained threading.

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ArminLinder · 2023-07-25 17:19

I did neanwhile also note, that there is a
TThread.Synchronize(AThread: TThread; AMethod: TThreadMethod) in
classes.inc (line: 1800). Seems that TThread.Synchronize calls it,
passing "self" to AThread.

Would that thing help me out?

Armin.

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Remy Lebeau · 2023-07-25 19:26

Quote from: Nimral on July 25, 2023, 07:19:59 pmI did neanwhile also
note, that there is a TThread.Synchronize(AThread: TThread; AMethod:
TThreadMethod) in classes.inc (line: 1800). Seems that
TThread.Synchronize calls it, passing "self" to AThread.

Would that thing help me out?

You already know that TThread.Synchronize() (any flavor of it) goes
through the main UI thread.  Sure, you could have multiple threads
syncing with each other using TThread.Synchronize(), but that will
still involve the main UI thread, and if the threads are not doing any
UI work than that just becomes an unnecessary bottleneck.  There are
better options/approaches for handling non-UI synchronization.

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Thaddy · 2023-07-26 10:03

Further more you are turning a threaded application into a non-
threaded application.
Which is common and silly.