C++ TUTORIALS - C++ Multithreading
C++ Multithreading
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Creating Threads:
Parameter | Description |
---|---|
thread | An opaque, unique identifier for the new thread returned by the subroutine. |
attr | An opaque attribute object that may be used to set thread attributes. You can specify a thread attributes object, or NULL for the default values. |
start_routine | The C++ routine that the thread will execute once it is created. |
arg | A single argument that may be passed to start_routine. It must be passed by reference as a pointer cast of type void. NULL may be used if no argument is to be passed. |
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Creating Threads:
#include <pthread.h> pthread_create (thread, attr, start_routine, arg)ADVERTISEMENTSTerminating Threads:
#include <pthread.h> pthread_exit (status)Example:
#include <iostream> #include <cstdlib> #include <pthread.h> using namespace std; #define NUM_THREADS 5 void *PrintHello(void *threadid) { long tid; tid = (long)threadid; cout << "Hello World! Thread ID, " << tid << endl; pthread_exit(NULL); } int main () { pthread_t threads[NUM_THREADS]; int rc; int i; for( i=0; i < NUM_THREADS; i++ ){ cout << "main() : creating thread, " << i << endl; rc = pthread_create(&threads[i], NULL, PrintHello, (void *)i); if (rc){ cout << "Error:unable to create thread," << rc << endl; exit(-1); } } pthread_exit(NULL); }
$gcc test.cpp -lpthread
main() : creating thread, 0 main() : creating thread, 1 main() : creating thread, 2 main() : creating thread, 3 main() : creating thread, 4 Hello World! Thread ID, 0 Hello World! Thread ID, 1 Hello World! Thread ID, 2 Hello World! Thread ID, 3 Hello World! Thread ID, 4Passing Arguments to Threads:
#include <iostream> #include <cstdlib> #include <pthread.h> using namespace std; #define NUM_THREADS 5 struct thread_data{ int thread_id; char *message; }; void *PrintHello(void *threadarg) { struct thread_data *my_data; my_data = (struct thread_data *) threadarg; cout << "Thread ID : " << my_data->thread_id ; cout << " Message : " << my_data->message << endl; pthread_exit(NULL); } int main () { pthread_t threads[NUM_THREADS]; struct thread_data td[NUM_THREADS]; int rc; int i; for( i=0; i < NUM_THREADS; i++ ){ cout <<"main() : creating thread, " << i << endl; td[i].thread_id = i; td[i].message = "This is message"; rc = pthread_create(&threads[i], NULL, PrintHello, (void *)&td[i]); if (rc){ cout << "Error:unable to create thread," << rc << endl; exit(-1); } } pthread_exit(NULL); }
main() : creating thread, 0 main() : creating thread, 1 main() : creating thread, 2 main() : creating thread, 3 main() : creating thread, 4 Thread ID : 3 Message : This is message Thread ID : 2 Message : This is message Thread ID : 0 Message : This is message Thread ID : 1 Message : This is message Thread ID : 4 Message : This is messageJoining and Detaching Threads:
pthread_join (threadid, status) pthread_detach (threadid)
#include <iostream> #include <cstdlib> #include <pthread.h> #include <unistd.h> using namespace std; #define NUM_THREADS 5 void *wait(void *t) { int i; long tid; tid = (long)t; sleep(1); cout << "Sleeping in thread " << endl; cout << "Thread with id : " << tid << " ...exiting " << endl; pthread_exit(NULL); } int main () { int rc; int i; pthread_t threads[NUM_THREADS]; pthread_attr_t attr; void *status; // Initialize and set thread joinable pthread_attr_init(&attr); pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE); for( i=0; i < NUM_THREADS; i++ ){ cout << "main() : creating thread, " << i << endl; rc = pthread_create(&threads[i], NULL, wait, (void *)i ); if (rc){ cout << "Error:unable to create thread," << rc << endl; exit(-1); } } // free attribute and wait for the other threads pthread_attr_destroy(&attr); for( i=0; i < NUM_THREADS; i++ ){ rc = pthread_join(threads[i], &status); if (rc){ cout << "Error:unable to join," << rc << endl; exit(-1); } cout << "Main: completed thread id :" << i ; cout << " exiting with status :" << status << endl; } cout << "Main: program exiting." << endl; pthread_exit(NULL); }
main() : creating thread, 0 main() : creating thread, 1 main() : creating thread, 2 main() : creating thread, 3 main() : creating thread, 4 Sleeping in thread Thread with id : 0 .... exiting Sleeping in thread Thread with id : 1 .... exiting Sleeping in thread Thread with id : 2 .... exiting Sleeping in thread Thread with id : 3 .... exiting Sleeping in thread Thread with id : 4 .... exiting Main: completed thread id :0 exiting with status :0 Main: completed thread id :1 exiting with status :0 Main: completed thread id :2 exiting with status :0 Main: completed thread id :3 exiting with status :0 Main: completed thread id :4 exiting with status :0 Main: program exiting.