Sven Barth schrieb:
Am 25.08.2010 23:07, schrieb José Mejuto:
On the other hand, if Unix needs one thread creation then it should be
automagically done in the initialization section of cthreads, do not ?
SB> This might indeed be a solution.
If windows have the same problem, threading system should be
initialized in... somewhere automagically as windows multithread is
always present.
This only solves one point (but is needed nevertheless).
As I've showed in the last message to Alexander yesterday evening you
need to initialize some things PER THREAD and I don't know whether
this can be automised. We might need to ask the FPC devs for help
regarding this. Perhaps the first time a threadvar in this new thread
is accessed might be a good possibilty, but I don't know (yet) how we
could track whether this is the first call, because threadvars are not
yet allocated (hen-egg-problem). I'll have to take a deeper look into
the threading system on Win32 :)
Regards,
Sven
I'm currently trying to summarize all aspects we discussed to add them
to the FreePascal Multithreading wiki page (see below) - did I forget
something that should be mentioned?
Thanks,
Alexander
External threads
To make Free Pascal's threading system to work properly, each newly
created FPC thread needs to be initialized (more exactly, the thread
local storage per thread needs to be initialized so threadvars and heap
are working). That is fully automatically done for you if you use
BeginThread (or indirectly by using the TThread class). However, if you
use threads that were created without BeginThread (i.e. external
threads), additional work (currently) might be required. External
threads also include those that were created in external C libraries
(.DLL/.so).
Things to consider when using external threads (might not be needed in
all or future compiler versions):
A) Initialize the FPC's threading system by creating a dummy thread:
{ initialise threading system }
with tc.create(false) do
begin
waitfor;
free;
end;
B) Make the runtime aware that your application uses multiple threads in
the first line of your application (.dpr):
IsMultithread:=true;
(This will make FPC routines to perform locks here and there.)
C) Do not use external threads at all - use FPC threads.
D) If for some reason this doesn't work for you, try this code in your
external thread function:
function ExternalThread(param: Pointer): LongInt; stdcall;
var
tm: TThreadManager;
begin
GetThreadManager(tm);
tm.AllocateThreadVars;
InitThread(100000000);
someFunc(param);
Result:=0;
end;
How to identify if your code is executed in an external thread context
1. Ask the OS for the ID of the current thread at your application's start
Win32: WriteLn('Thread ID=', GetCurrentThreadID);
Darwin: WriteLn('Thread ID=', GetThreadID);
Linux: Writeln('Thread ID=', TThreadID(pthread_self) );
2. Ask again for the ID of the current thread inside the thread function
and compare this by the result of step 1.
--
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