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Date: Sat, 29 Jun 2002 18:09:09 -0400
Subject: C++ Exceptions in Multithreaded Applications Crash
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Cc: khan AT nanotech DOT wisc DOT edu
To: cygwin AT cygwin DOT com
From: Lenny Primak <lprimak AT hope DOT nyc DOT ny DOT us>
Message-Id: <D61A7C0C-8BAC-11D6-8506-000393640A02@hope.nyc.ny.us>

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This has been submitted to GCC GNATS as PR/7168.

Using the G++ exception system from multiple threads corrupts the gcc's 
internal exception stack, due to not including the thread-specific 
exception context in the compile.
GCC Version: 2.95.3-5 from default Cygwin install.

I tried to re-compile gcc with --enable-threads=posix and with 
--enable-sjlj-exceptions
with no results.  The following program is used to determine if the 
exception context is thread-specific or not:


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#include <stdio.h>
#include <pthread.h>
#include <sys/poll.h>


extern "C" void *
__get_eh_context ();


static void* saved_eh_context = 0;

static void* func(void*) throw(char*)
{
	void* eh_cntxt = __get_eh_context();
	printf("func() - eh_context = %X\n", eh_cntxt);
	if(saved_eh_context == 0)
	{
		saved_eh_context = eh_cntxt;
	}
	else
	{
		if(eh_cntxt == saved_eh_context)
		{
			printf("FATAL: Identical Exception Stacks!\n");
		}
		else
		{
			printf("Great! Exception Stacks Differ.\n");
		}
	}
	int svar = 5;
	try {
		throw 1;
	}
	catch(char*)
	{
		printf("caught string\n");
	}
	catch(int)
	{
		// nothing
	}

	poll(0, 0, 5000);
	return 0;
}

int main()
{
	pthread_t thr, thr2;
	pthread_create(&thr, 0, &func, 0);
	poll(0, 0, 1000);
	pthread_create(&thr2, 0, &func, 0);
	pthread_join(thr, 0);
	pthread_join(thr2, 0);
	return 0;
}

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This prevents any sort of complex exception-sensitive multithreaded C++ 
programs to run in Cygwin/GCC environment.

Thanks for all your help,
Lenny


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