版权声明：本文为博主原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接和本声明。
多线程利用条件变量打印AB，ABC，奇偶数
1、条件变量
条件变量是多线程同步的一种方式。
2、两个线程打印ABAB
#include <iostream>
#include <cstdlib>
#include <pthread.h>
#include <unistd.h>
using namespace std;
#define NUM_THREADS 2
pthread_cond_t Aready = PTHREAD_COND_INITIALIZER; // A是否ready的条件
pthread_cond_t Bready = PTHREAD_COND_INITIALIZER; // B是否ready的条件
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
string nextchar = "A";
void* printerA(void*)
{
for (int i = 0; i < 10; i++) {
pthread_mutex_lock(&mutex);
while (nextchar != "A") {
pthread_cond_wait(&Aready, &mutex);
}
cout << nextchar;
nextchar = "B";
pthread_mutex_unlock(&mutex);
pthread_cond_signal(&Bready);
}
pthread_exit((void*) 1);
}
void* printerB(void*)
{
for(int i = 0; i < 10; i++) {
pthread_mutex_lock(&mutex);
while (nextchar != "B") {
pthread_cond_wait(&Bready, &mutex);
}
cout << nextchar;
nextchar = "A";
pthread_mutex_unlock(&mutex);
pthread_cond_signal(&Aready);
}
pthread_exit((void*) 2);
}
int main ()
{
int rc;
int i;
pthread_t threads[NUM_THREADS];
pthread_attr_t attr;
void *status;
// 初始化并设置线程为可连接的（joinable）
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
pthread_create(&threads[0], NULL, printerA, NULL);
pthread_create(&threads[1], NULL, printerB, NULL);
// 删除属性，并等待其他线程
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);
}
3、三个线程打印ABCABC
方法1:
#include <iostream>
#include <cstdlib>
#include <pthread.h>
#include <unistd.h>
using namespace std;
#define NUM_THREADS 3
pthread_cond_t Aready = PTHREAD_COND_INITIALIZER;
pthread_cond_t Bready = PTHREAD_COND_INITIALIZER;
pthread_cond_t Cready = PTHREAD_COND_INITIALIZER;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
string nextchar = "A";
void* printerA(void*)
{
for (int i = 0; i < 10; i++) {
pthread_mutex_lock(&mutex);
while (nextchar != "A") {
pthread_cond_wait(&Aready, &mutex);
}
cout << nextchar;
nextchar = "B";
pthread_mutex_unlock(&mutex);
pthread_cond_signal(&Bready);
}
pthread_exit((void*) 1);
}
void* printerB(void*)
{
for(int i = 0; i < 10; i++) {
pthread_mutex_lock(&mutex);
while (nextchar != "B") {
pthread_cond_wait(&Bready, &mutex);
}
cout << nextchar;
nextchar = "C";
pthread_mutex_unlock(&mutex);
pthread_cond_signal(&Cready);
}
pthread_exit((void*) 2);
}
void* printerC(void*)
{
for (int i = 0; i < 10; i++) {
pthread_mutex_lock(&mutex);
while (nextchar != "C") {
pthread_cond_wait(&Cready, &mutex);
}
cout << nextchar;
nextchar = "A";
pthread_mutex_unlock(&mutex);
pthread_cond_signal(&Aready);
}
pthread_exit((void*) 1);
}
int main ()
{
int rc;
int i;
pthread_t threads[NUM_THREADS];
pthread_attr_t attr;
void *status;
// 初始化并设置线程为可连接的（joinable）
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
pthread_create(&threads[0], NULL, printerA, NULL);
pthread_create(&threads[1], NULL, printerB, NULL);
pthread_create(&threads[2], NULL, printerC, NULL);
// 删除属性，并等待其他线程
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);
}
方法2:
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#define NUM_OF_CHARACTER 3
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
static int current_id = 0;
void* worker_thread(void *arg)
{
int thread_id = *(int *)arg;
for(int i=0; i<10; ++i){
pthread_mutex_lock(&mutex);
while(thread_id != current_id)
pthread_cond_wait(&cond, &mutex);
printf("%c", 'A'+thread_id);
current_id = (current_id + 1) % NUM_OF_CHARACTER;
pthread_mutex_unlock(&mutex);
pthread_cond_broadcast(&cond);
}
}
int main()
{
int thread_id[NUM_OF_CHARACTER] = {0, 1, 2};
pthread_t tids[NUM_OF_CHARACTER];
for(int i=0; i<NUM_OF_CHARACTER; ++i)
pthread_create(&tids[i], NULL, worker_thread, (void *)(thread_id+i));
for(int i=0; i<NUM_OF_CHARACTER; ++i)
pthread_join(tids[i], NULL);
return 0;
}4、两个线程打印奇偶数
#include <iostream>
#include <cstdlib>
#include <pthread.h>
#include <unistd.h>
using namespace std;
#define NUM_THREADS 2
pthread_cond_t Oddready = PTHREAD_COND_INITIALIZER; // 奇数ready
pthread_cond_t UnOddready = PTHREAD_COND_INITIALIZER; // 偶数ready
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int i = 0;
// 打印奇数
void* printerOdd(void*)
{
for (int index = 0; index < 10; index++) {
pthread_mutex_lock(&mutex);
while (i % 2 == 0) {
pthread_cond_wait(&Oddready, &mutex); // 当前是偶数的话，等待奇数ready条件满足
}
cout << "printOdd " << i << " ";
i++;
pthread_mutex_unlock(&mutex);
pthread_cond_signal(&UnOddready);
}
pthread_exit((void*) 1);
}
void* printerUnOdd(void*)
{
for(int index = 0; index < 10; index++) {
pthread_mutex_lock(&mutex);
while (i % 2 != 0) {
pthread_cond_wait(&UnOddready, &mutex); // 当前是奇数，等待偶数ready条件满足
}
cout << "printUnodd " << i << " ";
i++;
pthread_mutex_unlock(&mutex);
pthread_cond_signal(&Oddready); // 打印完偶数后，将条件变量“奇数ready” 置为true
}
pthread_exit((void*) 2);
}
int main ()
{
int rc;
int i;
pthread_t threads[NUM_THREADS];
pthread_attr_t attr;
void *status;
// 初始化并设置线程为可连接的（joinable）
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
pthread_create(&threads[0], NULL, printerOdd, NULL);
pthread_create(&threads[1], NULL, printerUnOdd, NULL);
// 删除属性，并等待其他线程
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 << endl;
cout << "Main: completed thread id :" << i ;
cout << " exiting with status :" << status << endl;
}
cout << "Main: program exiting." << endl;
pthread_exit(NULL);
}
5、3个线程，一个线程打印1、2、3，第二个线程打印4、5、6，第三个线程打印7、8、9，第一个线程打印10、11、12，以此类推...
#include <iostream>
#include <cstdlib>
#include <pthread.h>
#include <unistd.h>
using namespace std;
#define NUM_THREADS 3
pthread_cond_t ready = PTHREAD_COND_INITIALIZER; // 线程ready
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; // 条件变量ready的互斥锁
pthread_mutex_t i_mutex = PTHREAD_MUTEX_INITIALIZER; // 全局变量i的互斥锁
int i = 0; // 全局计数
int state = 0; // 全局进程状态ready标记，0 表示线程1ready，1 表示线程2 ready，2 表示线程3 ready
// 周期性地打印数字i, i + 1, i + 2
void printer(int thread_id)
{
pthread_mutex_lock(&i_mutex);
cout << "thread-" << thread_id << endl;
for (int index = 0; index < 3; index++) {
cout << i + 1 << " ";
i++;
}
cout << endl;
pthread_mutex_unlock(&i_mutex);
}
void* printer(void* arg)
{
int thread_id = *(int* )arg;
for(int index = 0; index < 10; index++) {
pthread_mutex_lock(&mutex);
while (thread_id % 3 != state) {
pthread_cond_wait(&ready, &mutex); // 如果thread_id % 3 ！= state，则对应的线程需要继续等待ready条件满足
}
printer(thread_id);
state = (state + 1) % 3; // 修改对应的线程ready标记
pthread_mutex_unlock(&mutex);
pthread_cond_broadcast(&ready); // 某一个线程打印完毕后，设置state值，并通知其他所有线程，其他所有线程按照state的值，检查是否自己等待的ready条件是否满足
}
pthread_exit((void*) 1); // 每一个线程的返回值设置为1；
}
int main ()
{
int rc;
int i;
int thread_ids[] = {0, 1, 2};
pthread_t threads[NUM_THREADS];
pthread_attr_t attr;
void *status;
// 初始化并设置线程为可连接的（joinable）
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
// 创建3个线程
for( i=0; i < NUM_THREADS; i++ ){
rc = pthread_create(&threads[i], NULL, printer, (void*)(thread_ids + i));
if (rc){
cout << "create thread falied: " << rc << endl;
exit(-1);
}
}
// 删除属性，并等待其他线程
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 << endl;
cout << "Main: completed thread id :" << i ;
cout << " exiting with status :" << status << endl;
}
cout << "Main: program exiting." << endl;
pthread_exit(NULL);
}