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boost thread example

 
 
Gary Wessle
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Posts: n/a
 
      11-20-2006

Hi

given the Boost thread example here
http://www-eleves-isia.cma.fr/docume...ple/thread.cpp

the code below attempts to run the example
thread while giving the user a prompt for data input.
I am failing to get the prompt while the thread is running, what am I
doing wrong?

thanks

************************************************** **************
#include <boost/thread/thread.hpp>
#include <boost/thread/xtime.hpp>
#include <iostream>
using namespace std;

struct thread_alarm
{
thread_alarm(int secs) : m_secs(secs) { }
void operator()()
{
boost:time xt;
boost:time_get(&xt, boost::TIME_UTC);
xt.sec += m_secs;

boost::thread::sleep(xt);

std::cout << "alarm sounded..." << std::endl;
}

int m_secs;
};

int main(){
int secs = 5;
std::cout << "setting alarm for 5 seconds..." << std::endl;
for( ;; ) {
cout << "type a number please:> " << endl;
int opt;
cin >> opt;
switch( opt ) {
case ( 1 ): {
thread_alarm alarm(secs);
boost::thread thrd(alarm);
thrd.join();
break;
}
case (99 ): cout << "Exiting ...\n"; break;
default: cout << "you typed " << opt << endl;
}
}
}
 
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Alf P. Steinbach
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Posts: n/a
 
      11-20-2006
* Gary Wessle:
> Hi
>
> given the Boost thread example here
> http://www-eleves-isia.cma.fr/docume...ple/thread.cpp
>
> the code below attempts to run the example
> thread while giving the user a prompt for data input.
> I am failing to get the prompt while the thread is running, what am I
> doing wrong?
>
> thanks
>
> ************************************************** **************
> #include <boost/thread/thread.hpp>
> #include <boost/thread/xtime.hpp>
> #include <iostream>
> using namespace std;
>
> struct thread_alarm
> {
> thread_alarm(int secs) : m_secs(secs) { }
> void operator()()
> {
> boost:time xt;
> boost:time_get(&xt, boost::TIME_UTC);
> xt.sec += m_secs;
>
> boost::thread::sleep(xt);
>
> std::cout << "alarm sounded..." << std::endl;
> }
>
> int m_secs;
> };
>
> int main(){
> int secs = 5;
> std::cout << "setting alarm for 5 seconds..." << std::endl;
> for( ;; ) {
> cout << "type a number please:> " << endl;
> int opt;
> cin >> opt;
> switch( opt ) {
> case ( 1 ): {
> thread_alarm alarm(secs);
> boost::thread thrd(alarm);
> thrd.join();
> break;
> }
> case (99 ): cout << "Exiting ...\n"; break;
> default: cout << "you typed " << opt << endl;
> }
> }
> }


The code above says to wait for the thread to finish before going on
with issuing the next prompt. From your description it seems the
program is doing exactly what the code says it should do. Btw., beware
of doing unsynchronized i/o in threads.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
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Gary Wessle
Guest
Posts: n/a
 
      11-20-2006
"Alf P. Steinbach" <(E-Mail Removed)> writes:

> * Gary Wessle:
> > Hi
> > given the Boost thread example here
> > http://www-eleves-isia.cma.fr/docume...ple/thread.cpp
> > the code below attempts to run the example
> > thread while giving the user a prompt for data input. I am failing
> > to get the prompt while the thread is running, what am I
> > doing wrong?
> > thanks
> > ************************************************** **************
> > #include <boost/thread/thread.hpp>
> > #include <boost/thread/xtime.hpp>
> > #include <iostream>
> > using namespace std;
> > struct thread_alarm
> > {
> > thread_alarm(int secs) : m_secs(secs) { }
> > void operator()()
> > {
> > boost:time xt;
> > boost:time_get(&xt, boost::TIME_UTC);
> > xt.sec += m_secs;
> > boost::thread::sleep(xt);
> > std::cout << "alarm sounded..." << std::endl;
> > }
> > int m_secs;
> > };
> > int main(){
> > int secs = 5;
> > std::cout << "setting alarm for 5 seconds..." << std::endl;
> > for( ;; ) {
> > cout << "type a number please:> " << endl;
> > int opt;
> > cin >> opt;
> > switch( opt ) {
> > case ( 1 ): {
> > thread_alarm alarm(secs);
> > boost::thread thrd(alarm);
> > thrd.join();
> > break;
> > }
> > case (99 ): cout << "Exiting ...\n"; break;
> > default: cout << "you typed " << opt << endl;
> > }
> > }
> > }

>
> The code above says to wait for the thread to finish before going on
> with issuing the next prompt. From your description it seems the
> program is doing exactly what the code says it should do. Btw.,
> beware of doing unsynchronized i/o in threads.


I need the code to issue the next prompt without waiting for the
thread to finish so that the user can select another "opt" while the
first thread job is still going.
 
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Gary Wessle
Guest
Posts: n/a
 
      11-20-2006
"Alf P. Steinbach" <(E-Mail Removed)> writes:

> * Gary Wessle:
> > Hi
> > given the Boost thread example here
> > http://www-eleves-isia.cma.fr/docume...ple/thread.cpp
> > the code below attempts to run the example
> > thread while giving the user a prompt for data input. I am failing
> > to get the prompt while the thread is running, what am I
> > doing wrong?
> > thanks
> > ************************************************** **************
> > #include <boost/thread/thread.hpp>
> > #include <boost/thread/xtime.hpp>
> > #include <iostream>
> > using namespace std;
> > struct thread_alarm
> > {
> > thread_alarm(int secs) : m_secs(secs) { }
> > void operator()()
> > {
> > boost:time xt;
> > boost:time_get(&xt, boost::TIME_UTC);
> > xt.sec += m_secs;
> > boost::thread::sleep(xt);
> > std::cout << "alarm sounded..." << std::endl;
> > }
> > int m_secs;
> > };
> > int main(){
> > int secs = 5;
> > std::cout << "setting alarm for 5 seconds..." << std::endl;
> > for( ;; ) {
> > cout << "type a number please:> " << endl;
> > int opt;
> > cin >> opt;
> > switch( opt ) {
> > case ( 1 ): {
> > thread_alarm alarm(secs);
> > boost::thread thrd(alarm);
> > thrd.join();
> > break;
> > }
> > case (99 ): cout << "Exiting ...\n"; break;
> > default: cout << "you typed " << opt << endl;
> > }
> > }
> > }

>
> The code above says to wait for the thread to finish before going on
> with issuing the next prompt. From your description it seems the
> program is doing exactly what the code says it should do. Btw.,
> beware of doing unsynchronized i/o in threads.
>


if I comment out the line
thrd.join();
it gives me the desired effect, is that the correct way to do it?
 
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dasjotre
Guest
Posts: n/a
 
      11-20-2006

Gary Wessle wrote:
> Hi


> struct thread_alarm
> {
> thread_alarm(int secs) : m_secs(secs) { }
> void operator()()
> {
> boost:time xt;
> boost:time_get(&xt, boost::TIME_UTC);
> xt.sec += m_secs;
>
> boost::thread::sleep(xt);


cout is not synchronized, it might
overlap with main thread's output

<snip>

> std::cout << "alarm sounded..." << std::endl;
> }


<snip>

> switch( opt ) {
> case ( 1 ): {
> thread_alarm alarm(secs);
> boost::thread thrd(alarm);


join will wait till thrd terminates, that doesn't seem
to be what you want

> thrd.join();
> break;
> }
> case (99 ): cout << "Exiting ...\n"; break;
> default: cout << "you typed " << opt << endl;


I believe you want the alarm to sound if the user
takes more than 5 seconds to type

In that case you will need to cancel the alarm
here. your current implementation of thread_alarm
doesn't provide such functionality

maybe looping around a flag for a fraction
of alarm time and then changing the flag
to exit the loop would do.

general idea:

struct thread_alarm
{
bool loop_;
thread_alarm(int secs) : m_secs(secs) , loop_(true){ }

void cancel(){ loop_= false; }

void operator()()
{
while(loop_ && m_secs)
{
boost:time xt;
boost:time_get(&xt, boost::TIME_UTC);
// sleep a second at a time
xt.sec += 1;
--m_secs;
boost::thread::sleep(xt);
}
if(loop_)
std::cout << "alarm sounded..." << std::endl;
}

int m_secs;
};

 
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