Re: Cancelling threads

[reentrant <reentrant@yahoo.com>]

For this particular case, in my experience the accept() returns (with some
error) if another thread close()s the socket returned by bind().

--- Ollie Leahy <ollie@mpt.ie> wrote:
> 
> 	Reading the FAQ I'm unsure about whether snapshots after
> 	snapshot-1999-11-02 implement asynchronous thread cancelling.
> 
> 	The FAQ makes the following statement:
> 
> Snapshot 99-11-02 or earlier only partially supports asynchronous
> cancellation.
> 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.
> 
> 
> 	Does this mean that snapshots after 99-11-02 do completely support
> 	asynchronous cancel? I'm using pthreads-2000-12-29.exe and
> 	the test program below blocks in the accept call and is not cancelled.
> 	The FAQ seems to imply that the thread will be terminated in libraries
> 	built after 1999-11-02, either:
> 
> 		a) This interpretation of the FAQ is not correct and there is
> 		no way to terminate a thread that is blocked in a system call.
> 
> 	or
> 
> 		b) There something else I need to do in order to terminate
> 		the thread blocking in accept()
> 
> 	Can you tell me which is the case?
> 
> 	For what it's worth, the thread is terminated when the same program
> 	is run under Linux.
> 
> 	Thanks,
> 		Ollie Leahy
> 
> 
> 
> 
> 
> 
> #include <stdio.h>
> #ifndef _WIN32
> #include <stdlib.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <netinet/in.h>
> #include <unistd.h>
> #include <string.h>
> #else
> #include <windows.h>
> #include <winsock.h>
> #define sleep(n) Sleep(n * 1000)
> #define close(n) closesocket(n)
> #endif
> 
> #include <pthread.h>
> 
> 
> 
> pthread_t	t1;
> pthread_t	t2;
> 
> void *
> thread1(void *dummy)
> {
> 	int oldtype;
> 	int ns, s;
> 	struct sockaddr_in sin;
> 	int	len;
> 
> 	pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &oldtype);
> 	if ((s = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
> 		printf("socket error");
> 		return NULL;
> 	}
> 	memset((char *)&sin, 0, sizeof(sin));
> 	sin.sin_family = AF_INET;
> 	sin.sin_addr.s_addr = INADDR_ANY;
> 	sin.sin_port = htons(7777);
> 	if (bind(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
> 		printf("bind failed.\n");
> 		return NULL;
> 	}
> 	if (listen(s,8)) {
> 		printf("listen error");
> 		return NULL;
> 	}
> 	printf("Ready to accept a connection\n");
> 	len = sizeof(struct sockaddr_in);
> 	if ((ns = accept(s, (struct sockaddr *)&sin, &len)) < 1) {
> 		printf("accept error");
> 		return NULL;
> 	}
> 	printf("Thread finishing normally.\n");
> 	close(s);
> 	close(ns);
> 	return NULL;
> }
> 
> 
> 
> int
> main(int	ac, char ** av)
> {
> #if defined (_WIN32)
> 	WSADATA junk;
> #endif
> 	void		* rValue = NULL;
> 
> #if defined (_WIN32)
> 
> 	if (WSAStartup(MAKEWORD(2, 0), &junk) != 0) {
> 		return -1;
> 	}
> #endif
> 
> 
> 	if (pthread_create(&t1, 0, thread1, 0)) {
> 		printf("pthread_create() thread1 failed\n");
> 		return -1;
> 	}
> 
> 	/*
> 	 * Give the thread time to block in accept()
> 	 */
> 	sleep(10);
> 	printf("Canceling thread.\n");
> 	pthread_cancel(t1);
> 	pthread_join(t1, &rValue);
> 
> 
> 
> #if defined (_WIN32)
> 	WSACleanup();
> #endif
> 
> 	return 0;
> }
> 


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