boost thread example

[Gary Wessle]

Hi

given the Boost thread example here
http://www-eleves-isia.cma.fr/documentation/BoostDoc/boost_1_29_0/libs/thread/example/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::xtime xt;
boost::xtime_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;
}
}
}

 

[Alf P. Steinbach]

* Gary Wessle:

Hi

given the Boost thread example here
http://www-eleves-isia.cma.fr/documentation/BoostDoc/boost_1_29_0/libs/thread/example/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::xtime xt;
boost::xtime_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.

 

[Gary Wessle]

* Gary Wessle:

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.

 

[Gary Wessle]

* Gary Wessle:

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?

 

[dasjotre]

Hi

struct thread_alarm
{
thread_alarm(int secs) : m_secs(secs) { }
void operator()()
{
boost::xtime xt;
boost::xtime_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

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

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::xtime xt;
boost::xtime_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;
};