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CVS date: 2003/04/20 16:42:06

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+                  =========================================

+                  PTHREADS-WIN32 Frequently Asked Questions

+                  =========================================

+

+INDEX

+-----

+

+Q 1	Should I use Cygwin or Mingw32 as a development environment?

+

+Q 2	Now that pthreads-win32 builds under Mingw32, why do I get

+	memory access violations?

+

+Q 3	How do I use pthread.dll for Win32 (Visual C++ 5.0)

+

+Q 4	Cancelation doesn't work for me, why?

+

+Q 5	Thread won't block after two calls to mutex_lock

+

+Q 6	How do I generate pthreadGCE.dll and libpthreadw32.a for use with Mingw32?

+

+=============================================================================

+

+Q 1	Should I use Cygwin or Mingw32 as a development environment?

+---

+

+A 1

+---

+Important: see Q2 also.

+

+In short, use Mingw32 with the MSVCRT library to build applications that use

+the DLL. Cygwin's own internal support for POSIX threads is growing. Consult

+that project's documentation for more information.

+

+Date: Mon, 07 Dec 1998 15:11:37 +0100

+From: Anders Norlander <anorland@hem2.passagen.se>

+To: Ross Johnson <rpj@ise.canberra.edu.au>

+Cc: pthreads-win32 <pthreads-win32@air.net.au>

+Subject: Re: pthreads-win32: TryEnterCriticalSection patch (fwd)

+

+Ross Johnson wrote:

+> 

+> Anders,

+> 

+> You said you're using GCC. Is that from cygwin32 or mingw32? What is your

+> environment (so I can perhaps help other people out)? We have problems

+> with cygwin32 et al that have been built on Win95. They're missing

+> _{begin,end}threadex.

+

+Ross,

+

+I use mingw32 when compiling pthreads-win32, but unlike most people I

+use MSVCRT as the C library instead of CRTDLL. For those that don't

+feel like configuring and building the necessary components themselves,

+Mumit Khan has released an add on for mingw32 to make it use MSVCRT40.

+It is available at his ftp site, follow the minw32 links at

+http://www.xraylith.wisc.edu/~khan/software/gnu-win32/

+

+For cygwin it is a completely different matter. I suppose

+pthreads-win32 uses _beginthreadex and _endthreadex because the Win32

+docs say that programs calling functions in the C library should not

+use CreateThread and ExitThread. However, this applies only to

+Microsoft's (and possibly others) multithreaded C libraries that need

+to keep track of per thread data, it does not apply to cygwin.

+This code solves the problem:

+

+/* Check for old and new versions of cygwin */

+#if defined(__CYGWIN32__) || defined(__CYGWIN__)

+/* Macro uses args so we can cast start_proc to LPTHREAD_START_ROUTINE

+   in order to avoid warnings because of return type */

+#define _beginthreadex(security, stack_size, start_proc, arg, flags,

+pid) \

+CreateThread(security, stack_size, (LPTHREAD_START_ROUTINE) start_proc,

+\

+             arg, flags, pid)

+#define _endthreadex ExitThread

+#endif

+

+I would be extremely careful using threads with cygwin, since it is

+not (yet) threadsafe.

+

+Regards,

+Anders

+

+------------------------------------------------------------------------------

+

+Q 2	Now that pthreads-win32 builds under Mingw32, why do I get

+---	memory access violations (segfaults)?

+

+A 2

+---

+Note: issue resolved.

+The latest Mingw32 package has thread-safe exception handling.

+Make sure you also read A 6 below to get a fully working build.

+

+

+The following email exchange describes the problem. Until this issue

+is resolved people without the Microsoft compiler can obtain the current

+MSVC prebuilt DLL (pthread.{dll,lib,h}) at:

+

+ftp://sources.redhat.com/pub/pthreads-win32/dll-latest 

+

+Date: Wed, 10 Feb 1999 13:21:01 -0000

+From: "Ruland, Kevin" <Kevin.Ruland@anheuser-busch.com>

+Reply-To: POSIX threads on Win32 <pthreads-win32@air.net.au>

+To: 'POSIX threads on Win32' <pthreads-win32@air.net.au>

+Subject: Mingw32 exceptions not thread safe.

+

+Hello everyone.

+

+I asked Mumit Khan, maintainer of egcs for mingw and assorted guru, about

+the Known Problem listed below.  

+

+> Known problems

+> --------------

+> 

+> There is an unresolved bug which shows up as a segmentation fault

+> (memory access violation) when the library is built using g++. Build

+> the test program "eyal1.c" and run with an argument of "2" or

+> greater. The argument is the number of threads to run, excluding the

+> main thread, so the bug appears with 2 or more worker threads.

+> 

+> Kevin Ruland has traced the exception to the try/catch blocks in

+> ptw32_threadStart().

+> 

+

+The official word is:

+

+<Quote Mumit Khan [khan@xraylith.wisc.edu]>

+EGCS-1.1.1 for win32 (either cygwin or crtdll/msvc runtimes) do not have

+thread-safe exception support. 

+

+For Cygwin, it'll happen when Cygwin runtime has mature thread safety and

+pthread is fully integrated. Then it's just a matter of rebuilding GCC (or

+just libgcc in this) with thread safe EH support.

+

+For Mingw crtdll/msvc, someone needs to write the thread-wrapper for win32

+threads. Anyone who knows win32 threads should be able to do this without

+much trouble at all. It's low on my priority list, so unless someone else

+volunteers, it'll have to wait.

+<\Quote>

+

+Kevin

+

+------------------------------------------------------------------------------

+

+Q 3	How do I use pthread.dll for Win32 (Visual C++ 5.0)

+---	

+

+A 3

+---

+>

+> I'm a "rookie" when it comes to your pthread implementation.  I'm currently

+> desperately trying to install the prebuilt .dll file into my MSVC compiler.

+> Could you please provide me with explicit instructions on how to do this (or

+> direct me to a resource(s) where I can acquire such information)?

+>

+> Thank you,

+>

+

+You should have a .dll, .lib, .def, and three .h files.

+

+The .dll can go in any directory listed in your PATH environment

+variable, so putting it into C:\WINDOWS should work.

+

+The .lib file can go in any directory listed in your LIB environment

+variable.

+

+The .h files can go in any directory listed in your INCLUDE

+environment variable.

+

+Or you might prefer to put the .lib and .h files into a new directory

+and add its path to LIB and INCLUDE. You can probably do this easiest

+by editing the file:-

+

+C:\Program Files\DevStudio\vc\bin\vcvars32.bat

+

+The .def file isn't used by anything in the pre-compiled version but 

+is included for information.

+

+Cheers.

+Ross

+

+------------------------------------------------------------------------------

+

+Q 4	Cancelation doesn't work for me, why?

+---

+

+A 4

+---

+> I'm investigating a problem regarding thread cancelation. The thread I want

+> to cancel has PTHREAD_CANCEL_ASYNCHRONOUS, however, this piece of code

+> blocks on the join():

+>

+>               if ((retv = Pthread_cancel( recvThread )) == 0)

+>               {

+>                       retv = Pthread_join( recvThread, 0 );

+>               }

+>

+> Pthread_* are just macro's; they call pthread_*.

+>

+> The thread recvThread seems to block on a select() call. It doesn't get

+> cancelled.

+>

+> Two questions:

+>

+> 1) is this normal behaviour?

+>

+> 2) if not, how does the cancel mechanism work? I'm not very familliar to

+> win32 programming, so I don't really understand how the *Event() family of

+> calls work.

+

+Async cancelation should be in versions post snapshot-1999-11-02

+of pthreads-win32 (currently only for x86 architectures).

+

+The answer to your first question is, normal POSIX behaviour would  

+be to asynchronously cancel the thread. However, even that doesn't

+guarantee cancelation as the standard only says it should be

+cancelled as soon as possible.

+

+However ...

+

+Snapshot 99-11-02 or earlier only partially supports asynchronous cancellation.

+Snapshots since then simulate async cancelation by poking the address of

+a cancelation routine into the PC of the threads context. This requires

+the thread to be resumed in some way for the cancelation to actually

+proceed. This is not true async cancelation, but it is as close as we've

+been able to get to it.

+

+If the thread you're trying to cancel is blocked (for instance, it could be

+waiting for data from the network), it will only get cancelled when it unblocks

+(when the data arrives). Unfortunately, there is no way to do so from

+outside the thread.

+

+Using deferred cancelation would normally be the way to go, however,

+even though the POSIX threads standard lists a number of C library

+functions that are defined as deferred cancelation points, there is

+no hookup between those which are provided by Windows and the

+pthreads-win32 library.

+

+Incidently, it's worth noting for code portability that the POSIX

+threads standard list doesn't include "select" because (as I read in

+Butenhof) it isn't part of POSIX.

+

+Effectively, the only cancelation points that pthreads-win32 can

+recognise are those the library implements itself, ie.

+        

+        pthread_testcancel

+        pthread_cond_wait

+        pthread_cond_timedwait

+	pthread_join

+        sem_wait

+        pthread_delay_np

+

+Pthreads-win32 also provides two functions that allow you to create

+cancelation points within your application, but only for cases where

+a thread is going to block on a Win32 handle. These are:

+

+        pthreadCancelableWait(HANDLE waitHandle) /* Infinite wait */

+ 

+        pthreadCancelableTimedWait(HANDLE waitHandle, DWORD timeout)

+

+Regards.

+Ross

+

+------------------------------------------------------------------------------

+ 

+Q 5	Thread won't block after two calls to mutex_lock

+---

+ 

+A 5

+---

+> i was testing this pthread for win32 in my prog.

+> when i checked if it was blocking mutex_lock calls, i was surprised when it

+> didnt lock

+> 

+> pthread_mutex_t DBlock;

+> 

+> pthread_mutex_init( &DBlock, NULL );

+> pthread_mutex_lock( &DBlock );

+> pthread_mutex_lock( &DBlock );

+> 

+> ^^ these two calls didnt block

+

+POSIX leaves the result "undefined" for a thread that tries

+to recursively lock the same mutex (one that it owns already).

+That means the actual semantics are left up to the

+implementation, but should not be relied upon for code that

+will be ported to different POSIX threads implementations.

+

+In the pthreads-win32 implementation a thread won't deadlock

+itself by relocking the mutex. Subsequent calls to

+pthread_mutex_lock() as in your example above increment

+the lock count but the thread continues on. Consequently,

+the thread must ensure that it unlocks the mutex once for

+each lock operation. That is, pthreads-win32 mutexes are

+always recursive.

+

+You may want to look at the other synchronisation devices

+available in the library, such as condition variables or

+read-write locks.

+

+Ross

+

+------------------------------------------------------------------------------

+ 

+Q 6	How do I generate pthreadGCE.dll and libpthreadw32.a for use with Mingw32?

+---

+ 

+A 6

+---

+Once you've followed Thomas Pfaff's instructions below to fix

+Mingw32, then you can simply run "make" to build the library and dll.

+

+

+From - Sat Dec  9 22:56:10 2000

+From: "Thomas Pfaff" <tpfaff@gmx.net>

+To: <mingw-users@lists.sourceforge.net>, <pthreads-win32@sources.redhat.com>

+Subject: mingw32 DLLs, threads and exceptions HOWTO

+Date: Thu, 7 Dec 2000 11:12:43 +0100

+

+Dear all,

+

+this is a summary that should help users to have thread safe exception

+handling over DLL exported functions.

+If you don't care about c++ exceptions you can stop reading here.

+

+The first time i struggled with c++ exceptions was when i tried to throw an

+exception in a dll exported function where the exception handler resides in

+the program module.

+Instead of catching the exception the program stopped with an abnormal

+termination.

+The reason was that the exception code is in libgcc.a. Since this is a

+static library the code and some static variables are both in the dll and in

+the program module, each module runs in its own context.

+It was Franco Bez that pointed me in the right direction, that is convert

+libgcc.a into a dll.

+

+That done i tried to build the pthreads-win32 library, but some tests failed

+with an access violation. Due to the fact that the dll was not build

+was -mthreads support, eh_context_static instead of eh_context_specific (the

+mthreads version) was used for exception handling.

+I did a rebuild of the gcc dll with -mthreads, now all tests are passed

+(except a nonportable exception test that relies on a MSVC feature).

+

+To build the gcc dll i did the following steps.

+

+1. create a temporary directory libgcc

+2. copy libgcc.a from gcc-2.95.2\lib\gcc-lib\i386-mingw32\gcc-2.95.2 to that

+directory

+3. ar -x libgcc.a

+4. create a directory tmp and move __main.o, _exit.o and __dummy.o in that

+directory

+5. build the dll

+gcc -shared -mthreads -o gcc.dll *.o

+strip gcc.dll

+Move this dll into your gcc\bin directory

+6. Move _chkstk.o and frame.o to the tmp directory, otherwise you break the

+builtin alloca.

+7. Build the import library libgcc.a

+dllwrap --export-all --dllname=gcc.dll --output-def=libgcc.def --output-lib=

+libgcc.a *.o

+ar -q libgcc.a tmp/*.o

+strip --strip-debug libgcc.a

+ranlib libgcc.a

+8. save your old libgcc.a, copy the new libgcc.a into

+gcc-2.95.2\lib\gcc-lib\i386-mingw32\gcc-2.95.2

+

+I am using gcc-2.95.2-1 with Mumits patched binutils-19990818-1and msvcrt

+runtime-2000-03-27.

+I don't know if this is still required with the current binutils and gcc

+since i have seen no sources until now.

+

+I believe that these steps are at least necessary if you are trying to use

+the pthreads-win32 library (which is required if you want to use gtk+ on

+win32).

+They will make mingw32 a real replacement for MSVC (at least for me).

+

+What is left:

+

+1. Include the mingwm10.dll function into the gcc.dll to have only one dll

+left.

+2. make -mthreads and -fnative-struct default compiler options.

+3. convert libstdc++ to a dll by adding the declspec dllexport and dllimport

+to every class definition.

+

+Regards,

+    Thomas

+

+------------------------------------------------------------------------------

+