Pthread and keyboard - c++

Question

I want to know how to run a thread to sleep some time every time I press a key. For example, if I press the same key twice, it should have two threads to sleep for a while.
I MUST use pthreads and C++.
Honestly I have tried many ways but I still do not know how to solve it.
Sorry if my english is not very good :)
UPDATE
This is my code:
#include <pthread.h>
#include <iostream>
#include <unistd.h>
using namespace std;
pthread_mutex_t mutex;
pthread_cond_t cond;
int a;
void* executer2(void*)
{
pthread_mutex_lock(&mutex);
while (a > 0) {
pthread_cond_wait(&cond, &mutex);
}
cout << "Thread: " << pthread_self() << endl;
sleep(a);
pthread_mutex_unlock(&mutex);
}
void* executer(void*)
{
int key;
while (1) {
pthread_mutex_lock(&mutex);
key = cin.get();
if (key == 'a') {
cout << "Sleep for 4 seconds" << endl;
a = 4;
} else if (key == 'b') {
cout << "Sleep for 8 seconds" << endl;
a = 8;
} else {
cout << "Sleep for 2 seconds" << endl;
a = 2;
}
pthread_cond_signal(&cond);
pthread_mutex_unlock(&mutex);
sleep(1);
}
}
int main()
{
pthread_t tr, t;
pthread_attr_t attr;
pthread_mutex_init(&mutex, NULL);
pthread_cond_init(&cond, NULL);
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
pthread_create(&tr, &attr, executer, NULL);
pthread_create(&t, &attr, executer2, NULL);
pthread_join(tr, NULL);
pthread_join(t, NULL);
}

Answer 1

since you want to create a thread each time you press a key, and that the keypress handler is in executer, you should move the code to create executer2 in executer.
executer is made to sleep 1 sec. after reading a key press, but it seems that's not what you want. Just remove that call to sleep(1) to get an immediate response
the code of executer seems to indicate that you wish to modulate the time spent sleeping by the thread depending on the input key. You can pass the sleep time as a parameter to executer2, as indicated by the void * parameter of that function. The idea is to cast the time value to a void *, pass it at thread creation time, and cast it back to int within executer2:
// executer2 thread creation
pthread_create(&t, &attr, executer2,(void *)a);
and in executer2:
void *executer2(void *arg){
int a = (int)arg;
// ...
The thread creation code should go after the switch in executer2, and you should not need the global a variable anymore.
you are currently using a mutex to lock the code of executer2. This will prevent all the sleeping threads to sleep together at the same time. You will have to remove the lock to allow them to sleep concurrently (but leave the lock around the text output).
you say that you wish a C++ solution. You could benefit from using the thread library from the stl, which wraps the OS thread primitives (pthreads in your case) with higher level constructs and are easier to manipulate, especially for parameters. It would be a good exercise to convert your programme to use this library once you have the current code working.