Android NDK pthreads詳細使用
寫這個博客的原因是我要寫如何使用FFmpeg播放視頻，因為同時需要播放音頻和視頻所以需要開啟線程，並設置生產者和消費者的關系。
好了直接上整體
1.開啟和銷毀線程
pthread_create函數能夠創建線程，第一個參數是線程的引用，第二個是線程的屬性，一般為NULL，第三個為線程運行的函數，第四個是給線程運行函數的參數
pthread_create又是開啟線程，只要運行了這個函數線程就會運行起來，也就是運行第三個參數所代表的函數
pthread_t pthreads; pthread_create(&pthreads, NULL, threadFunc, (void *) "zzw");
等待線程完成和返回參數，這個如果開啟線程只有一個可以不寫，但是如果有多個線程這個就必須要寫，不寫的話只會運行第一個線程
int retvalue;
pthread_join(pthreads,(void**)&retvalue);
if(retvalue!=0){
__android_log_print(ANDROID_LOG_ERROR,"hello","thread error occurred");
}我們再來看看線程運行函數，這個他可以獲取參數，並且能能夠提前結束線程
void threadFunc(void arg){
char* str=(char*)arg; for(int i=0;i<3;i++){ __android_log_print(ANDROID_LOG_VERBOSE,"hello","i = %d arg = %s",i,str); //線程自殺，需要返回參數 //pthread_exit((void*)2); //線程他殺 //pthread_cancel() } return (void *) 0;
}
完整例子代碼
#include <jni.h>
#include <string>
#include <android/log.h>
#define LOGE(FORMAT,...) android_log_print(ANDROID_LOG_ERROR,"LC XXX",FORMAT,##VA_ARGS__);
extern "C"
JNIEXPORT jstring
JNICALL
Java_com_example_zth_ndkthread_MainActivity_stringFromJNI(
JNIEnv env,
jobject /
std::string hello = "Hello from C++";
return env->NewStringUTF(hello.c_str());
}
void threadFunc(void arg){
char* str=(char*)arg;
for(int i=0;i<3;i++){
__android_log_print(ANDROID_LOG_VERBOSE,"hello","i = %d arg = %s",i,str);
//線程自殺，需要返回參數
//pthread_exit((void*)2);
//線程他殺
//pthread_cancel()
}
return (void *) 0;}
extern "C"
JNIEXPORT void JNICALL
Java_com_example_zth_ndkthread_MainActivity_startNativeThread(JNIEnv* env, jobject thiz,jint count) {
pthread_t pthreads;
pthread_create(&pthreads, NULL, threadFunc, (void *) "zzw");
int retvalue;
pthread_join(pthreads,(void**)&retvalue);
if(retvalue!=0){
__android_log_print(ANDROID_LOG_ERROR,"hello","thread error occurred");
}}
2.互斥鎖
互斥鎖指的是它能夠鎖住一段代碼，使得這段代碼在解鎖之前不能再被執行一次，
初始化
pthread_mutex_t pthread_mutex;
if(pthread_mutex_init(&pthread_mutex,NULL)!=0)
return;開啟線程時把互斥鎖傳給線程運行函數
for(int i=0;i<count;i++){
pthread_create(&pthreads[i],NULL,threadFunc,&pthread_mutex);
}我們再來看看線程運行函數
取出互斥鎖並上鎖
pthread_mutex_t* pthread_mutex=(pthread_mutex_t*)arg;
pthread_mutex_lock(pthread_mutex);然後一段代碼
for(int i=0;i<3;i++){
__android_log_print(ANDROID_LOG_VERBOSE,"hello","i = %d",i);
}
__android_log_print(ANDROID_LOG_VERBOSE,"hello","————————————");解鎖
pthread_mutex_unlock(pthread_mutex);
最後銷毀互斥鎖
pthread_mutex_destroy(&pthread_mutex);運行效果如下
03-02 14:25:58.346 10022-10077/com.example.zth.ndkthread V/hello: i = 0
03-02 14:25:58.346 10022-10077/com.example.zth.ndkthread V/hello: i = 1
03-02 14:25:58.346 10022-10077/com.example.zth.ndkthread V/hello: i = 2
03-02 14:25:58.346 10022-10077/com.example.zth.ndkthread V/hello: ------------------------
03-02 14:25:58.346 10022-10078/com.example.zth.ndkthread V/hello: i = 0
03-02 14:25:58.346 10022-10078/com.example.zth.ndkthread V/hello: i = 1
03-02 14:25:58.346 10022-10078/com.example.zth.ndkthread V/hello: i = 2
03-02 14:25:58.346 10022-10078/com.example.zth.ndkthread V/hello: ------------------------
03-02 14:25:58.347 10022-10079/com.example.zth.ndkthread V/hello: i = 0
03-02 14:25:58.347 10022-10079/com.example.zth.ndkthread V/hello: i = 1
03-02 14:25:58.347 10022-10079/com.example.zth.ndkthread V/hello: i = 2
03-02 14:25:58.347 10022-10079/com.example.zth.ndkthread V/hello: ————————————
如果我們沒有加鎖呢
pthread_mutex_t* pthread_mutex=(pthread_mutex_t*)arg;// pthread_mutex_lock(pthread_mutex);
for(int i=0;i<3;i++){
android_log_print(ANDROID_LOG_VERBOSE,"hello","i = %d",i);
}
android_log_print(ANDROID_LOG_VERBOSE,"hello","------------------------");
// pthread_mutex_unlock(pthread_mutex);
結果如下
03-02 14:36:50.035 13815-13993/com.example.zth.ndkthread V/hello: i = 0
03-02 14:36:50.035 13815-13993/com.example.zth.ndkthread V/hello: i = 1
03-02 14:36:50.035 13815-13993/com.example.zth.ndkthread V/hello: i = 2
03-02 14:36:50.035 13815-13993/com.example.zth.ndkthread V/hello: ------------------------
03-02 14:36:50.035 13815-13994/com.example.zth.ndkthread V/hello: i = 0
03-02 14:36:50.035 13815-13994/com.example.zth.ndkthread V/hello: i = 1
03-02 14:36:50.035 13815-13994/com.example.zth.ndkthread V/hello: i = 2
03-02 14:36:50.035 13815-13995/com.example.zth.ndkthread V/hello: i = 0
03-02 14:36:50.035 13815-13994/com.example.zth.ndkthread V/hello: ------------------------
03-02 14:36:50.035 13815-13995/com.example.zth.ndkthread V/hello: i = 1
03-02 14:36:50.035 13815-13995/com.example.zth.ndkthread V/hello: i = 2
03-02 14:36:50.035 13815-13995/com.example.zth.ndkthread V/hello: ------------------------
所以互斥鎖是先讓一個線程做完，然後另外一個線程做。
例子代碼：
#include <jni.h>
#include <string>
#include <android/log.h>
#include "pthread.h"
#define LOGE(FORMAT,...) android_log_print(ANDROID_LOG_ERROR,"LC XXX",FORMAT,##VA_ARGS__);
extern "C"
JNIEXPORT jstring
JNICALL
Java_com_example_zth_ndkthread_MainActivity_stringFromJNI(
JNIEnv env,
jobject / this */) {
std::string hello = "Hello from C++";
return env->NewStringUTF(hello.c_str());
}
void threadFunc(void arg){
pthread_mutex_t* pthread_mutex=(pthread_mutex_t*)arg;
pthread_mutex_lock(pthread_mutex);
for(int i=0;i<3;i++){
__android_log_print(ANDROID_LOG_VERBOSE,"hello","i = %d",i);
}
__android_log_print(ANDROID_LOG_VERBOSE,"hello","------------------------");
pthread_mutex_unlock(pthread_mutex);
return (void *) 0;}
extern "C"
JNIEXPORT void JNICALL
Java_com_example_zth_ndkthread_MainActivity_startNativeThread(JNIEnv* env, jobject thiz,jint count) {
pthread_mutex_t pthread_mutex;
if(pthread_mutex_init(&pthread_mutex,NULL)!=0)
return;
pthread_t pthreads[count];
for(int i=0;i<count;i++){
pthread_create(&pthreads[i],NULL,threadFunc,&pthread_mutex);
}
for(int i=0;i<count;i++){
int retvalue=0;
pthread_join(pthreads[i],(void**)&retvalue);
if(retvalue!=0){
__android_log_print(ANDROID_LOG_ERROR,"hello","thread error occurred");
}
}
pthread_mutex_destroy(&pthread_mutex);}
3.條件變量
視頻解碼的繪制使用的就是生產者—消費者的模式。比如說我們生產者生成的產品，放到一個隊列裏面，當生產者生產出產品的時候就會發送信號通知消費者去消費
這個條件變量能夠喚醒線程運行
初始化
pthread_cond_init(&c,NULL);
開啟生成者線程和消費者線程
pthread_create(&thread_producer, NULL, produce, (void *) "producer");
pthread_create(&thread_comsumer, NULL, comsume, (void *) "comsumer");循環生產產品，然後提醒消費者
for(;;){
pthread_mutex_lock(&m);
productNum++;
__android_log_print(ANDROID_LOG_VERBOSE,"hello","i = %d",productNum);
pthread_cond_signal(&c);
pthread_mutex_unlock(&m);
}消費者線程如果發現沒有產品就等待條件變量提醒，，如果有產品就消費掉
pthread_mutex_lock(&m);
while(productNum == 0){
pthread_cond_wait(&c,&m);
}
productNum--;
__android_log_print(ANDROID_LOG_VERBOSE,"hello","i = %d",productNum);
pthread_mutex_unlock(&m);註意生成者與消費者線程運行的全過程都在互斥鎖下，都是按順序一一執行的，這樣對於全局變量productNum的計算就不會錯誤，並且通過一個線程執行pthread_cond_signal來觸發另一個線程執行
例子代碼
#include <jni.h>
#include <string>
#include <android/log.h>
#include "pthread.h"
#define LOGE(FORMAT,...) android_log_print(ANDROID_LOG_ERROR,"LC XXX",FORMAT,##VA_ARGS__);
extern "C"
JNIEXPORT jstring
JNICALL
Java_com_example_zth_ndkthread_MainActivity_stringFromJNI(
JNIEnv env,
jobject / this */) {
std::string hello = "Hello from C++";
return env->NewStringUTF(hello.c_str());
}
int productNum = 0;
pthread_mutex_t m;
pthread_cond_t c;
void produce(void arg){
char no = (char)arg;
for(;;){
pthread_mutex_lock(&m);
productNum++;
__android_log_print(ANDROID_LOG_VERBOSE,"hello","i = %d",productNum);
pthread_cond_signal(&c);
pthread_mutex_unlock(&m);
}}
void comsume(void arg){
char no = (char)arg;
for(;;){
pthread_mutex_lock(&m);
while(productNum == 0){
pthread_cond_wait(&c,&m);
}
productNum--;
__android_log_print(ANDROID_LOG_VERBOSE,"hello","i = %d",productNum);
pthread_mutex_unlock(&m);
}}
extern "C"
JNIEXPORT void JNICALL
Java_com_example_zth_ndkthread_MainActivity_startNativeThread(JNIEnv* env, jobject thiz,jint count) {
pthread_mutex_init(&m,NULL);
pthread_cond_init(&c,NULL);
pthread_t thread_producer;
pthread_t thread_comsumer;
pthread_create(&thread_producer, NULL, produce, (void *) "producer");
pthread_create(&thread_comsumer, NULL, comsume, (void *) "comsumer");
pthread_join(thread_producer,NULL);
pthread_join(thread_comsumer,NULL);
pthread_mutex_destroy(&m);
pthread_cond_destroy(&c);}
參考文章
https://www.jianshu.com/p/453d12c16885
http://blog.csdn.net/lxmhuendan/article/details/11967593
Android NDK pthreads詳細使用