Hi Philipp,
Philipp Lohmann - Sun Germany wrote:
How sure are you that thread switching can only happen in a "message
related function" ? Then what exactly constitutes a "message related"
Quite sure, just take a look at
http://msdn2.microsoft.com/en-us/library/ms644950.aspx
somewhere in the middle you find:
"Messages sent between threads are processed only when the receiving
thread executes message retrieval code."
This actually is the documentation for "SendMessage" ...
function ? Most likely the main thread would be either waiting for the
solar mutex (basically in osl_acquireMutex, that is probably in
EnterCriticalSection) or it would wait for events and has released the
solar mutex anyway (this is the most likely case, the main thread is
yielding and therefore has released the solar mutex) and waits in
GetMessage anyway, which certainly qualifies as "message realated" ;-) .
The first example basically matches what I tried to outline in my other
mail. E.g.
- The main-thread (the one owning the invisible window) is not in VCL.
- Another thread wants to create e.g. a window. It therefor locks the
Solar Mutex, calls into VCL and eventually blocks in "SendMessage",
waiting for the main-thread to receive the non-queued message.
- The main-thread comes back and tries to lock the Solar Mutex as well,
before actually entering VCL.
=> deadlock!
The second example is not much better. E.g.
- The main-thread is in VCL, had locked the Solar Mutex before calling
in, eventually releases the Solar Mutex directly before calling
"GetMessage", where it blocks.
- Another thread wants to create a window. It therefor locks the now
unlocked Solar Mutex, calls into VCL and eventually blocks in
"SendMessage", keeping the Solar Mutex and waiting for the main-thread
to receive the non-queued message.
- The main-thread falls out of GetMessage and tries to reacquire the
Solar Mutex.
=> deadlock!
Kind regards, pl
IMHO, the current approach is flawed.
Kay
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