How do i stop a thread?

[cftmon]

I want my thread to stop as soon as the main thread finishes. My thread contains code that changes the channel of a wireless adapter through ioctl calls.It contains a infinite loop.


Problem is that the thread still keeps running even after i call pthread_exit. Is something missing here?I tried pthread_kill and it exits the entire program instead.


void* changeChannel(void* args)
{

while(true)
{
//change channel here..
}

}
//main thread
pthread_t chgchannel;
int t = pthread_create(&chgchannel,NULL,&changeChannel, (void *)devName.c_str() );

if(t)
{
std::cout << "fail" << std::endl;
}

pcap_loop(handler,100,procPacket,NULL); // packet capturing
std::cout << "got:"+client << std::endl;
std::cout << "finished" << std::endl;
pthread_exit(&chgchannel);

[MadCow108]

see pthread_cancel
http://www.kernel.org/doc/man-pages/online/pages/man3/pthread_cancel.3.html

you could also use a global/threadlocal variable for the while loop which gets changed by the mainthread or on signal from main thread (from pthread_kill)


void thread() {
while(keep_running){
...
}
}

[cftmon]

somehow using pthread_cancel and/or global variables give me segmentation fault :confused:

void thread() {
while(sig!=-1){
...
}
}

[MadCow108]

do you still have this in the code?
pthread_exit(&chgchannel);
this is wrong, pthread_exit takes a pointer the return value, not the a pointer to the thread handle

also (void *)devName.c_str() in pthread_create is unsafe.
if devName goes out of scope before the thread has copied it you have a problem.

else please post more code.

[cftmon]

do you still have this in the code?
pthread_exit(&chgchannel);
this is wrong, pthread_exit takes a pointer the return value, not the a pointer to the thread handle

also (void *)devName.c_str() in pthread_create is unsafe.
if devName goes out of scope before the thread has copied it you have a problem.

else please post more code.

thanks for the info, yea i removed pthread_exit, i need to use (void *)devName.c_str() as the thread requires a device name to call the driver.Or the compiler would complain

As for the segmentation faults, it was not the threading problem but rather my codes went haywire in a thread.I confirmed this with a simple cout in the thread.
Strange thing is that it worked okay when i fork() it.
I post the code for everyone to see(scrutinize):lolflag: Anyone good with ioctl calls? I am still new to it.



#include <linux/wireless.h>
//changing of channels
void* changeChannel(void* args)
{

char* devName = (char*) args;
int channel = 0;
int fd = sock_open();
struct iw_freq freq;
freq.e=0;
while(true)
{

struct iwreq* reqDev;
sleep(2);

freq.m =channel++;
freq.flags=IW_FREQ_FIXED;
reqDev->u.freq = freq;//segfault seeems to come from here?
strncpy(reqDev->ifr_name, devName, IFNAMSIZ);
ioctl(fd, SIOCSIWFREQ , reqDev);
if(channel==14)
{
channel=0;
}
}
}

//here create a thread to changing channels, and start capturing packets. devName is a std::string that contains a device name
pthread_t chgchannel;
int t = pthread_create(&chgchannel,NULL,&changeChannel, (void *)devName.c_str() );
if(t)
{
std::cout << "fail" << std::endl;
}
pcap_loop(handler,200,procPacket,NULL);
std::cout << "got:"+client << std::endl;
std::cout << "finished" << std::endl;
pthread_cancel(chgchannel);