本文起初主要想写个示例实测下pthread_mutex_lock和pthread_mutex_trylock区别。在linux机器上很快就over了,但是想了一下,pthread是unix系的,在windows没办法直接运行代码很不方便。于是想到了android,windows上安装ndk,手机root就可以跑pthread代码咯。。。
demo
lock和trylock的区别也很好理解:,前者是阻塞的,死等知道互斥锁被释放;而后者则更加灵活,浅尝辄止,做个尝试不行则干其他事情去。。测试代码pt_lock.c如下:
- #include <stdio.h>
- #include <stdlib.h>
- #include <string.h>
- #include <pthread.h>
- #include <unistd.h>
- #include <sys/types.h>
-
- typedef pthread_t pt_t;
- typedef unsigned int uint_t;
-
- pthread_mutex_t mt = PTHREAD_MUTEX_INITIALIZER;
-
- void lock_func(void* arg)
- {
- pid_t pid; //process
- pt_t tid; // thread
-
- pid = getpid();
- tid = pthread_self();
-
- printf("want to lock mutex, msg=%s, tid=%u\n", (char*)arg, (uint_t)tid);
-
- pthread_mutex_lock( &mt );
- printf("I[tid=%u] am using, (*|^_^|*)\n", (uint_t)tid);
- sleep(10);
- pthread_mutex_unlock( &mt );
- }
-
- void try_lock_func(void* arg)
- {
- uint_t tid = (uint_t)pthread_self();
- int counter = 0;
-
- while ( pthread_mutex_trylock( &mt ) )
- {
- sleep(1);
- ++counter;
-
- printf("after sleep 1s, i [tid=%u] want to try again, iter=%d.\n", tid, counter);
- }
- printf("It is my[tid=%u] turn, so long i waited...msg=%s\n", tid, (char*)arg);
- pthread_mutex_unlock( &mt );
- }
-
- #define XX_CREATE_FAILED(err) \
- printf("create thread error : %s\n", strerror(err));\
- return 1;
-
- int main()
- {
- int rc;
- pt_t pt1, pt2, pt3;
-
- const char* msg1 = "block";
- const char* msg2 = "unblock";
-
- rc = pthread_create(&pt1, NULL, (void*)&lock_func, (void*)msg1); if (rc != 0)
- {
- XX_CREATE_FAILED(rc);
- }
-
- rc = pthread_create(&pt2, NULL, (void*)&lock_func, (void*)msg1); if (rc != 0)
- {
- XX_CREATE_FAILED(rc);
- }
- sleep(1);
-
- rc = pthread_create(&pt3, NULL, (void*)&try_lock_func, (void*)msg2); if (rc != 0)
- {
- XX_CREATE_FAILED(rc);
- }
-
- pthread_join(pt1, NULL);
- pthread_join(pt2, NULL);
- pthread_join(pt3, NULL);
- return 0;
- }
代码思路也很好理解:创建三个线程,1和2通过lock方式去争抢mt互斥锁,3线程则灵活,每隔1秒去检测下mt互斥锁是否可以用,不会阻塞。线程1或者2占有mt的时间为10秒。
linux run
- xx@h10-1-152-72:~/peteryfren/cpp/pthread> gcc -Wall -o pt_lock pt_lock.c -lpthread
- xx@h10-1-152-72:~/peteryfren/cpp/pthread> ./pt_lock
输出结果与预期一致,id=1082132800线程先占有mt,10s内线程tid=1090525504阻塞,而线程tid=1098918208每隔1s测试下mt可用性。
- want to lock mutex, msg=block, tid=1082132800
- I[tid=1082132800] am using, (*|^_^|*)
- want to lock mutex, msg=block, tid=1090525504
- after sleep 1s, i [tid=1098918208] want to try again, iter=1.
- after sleep 1s, i [tid=1098918208] want to try again, iter=2.
- after sleep 1s, i [tid=1098918208] want to try again, iter=3.
- after sleep 1s, i [tid=1098918208] want to try again, iter=4.
- after sleep 1s, i [tid=1098918208] want to try again, iter=5.
- after sleep 1s, i [tid=1098918208] want to try again, iter=6.
- after sleep 1s, i [tid=1098918208] want to try again, iter=7.
- after sleep 1s, i [tid=1098918208] want to try again, iter=8.
- I[tid=1090525504] am using, (*|^_^|*)
- after sleep 1s, i [tid=1098918208] want to try again, iter=9.
- after sleep 1s, i [tid=1098918208] want to try again, iter=10.
- after sleep 1s, i [tid=1098918208] want to try again, iter=11.
- after sleep 1s, i [tid=1098918208] want to try again, iter=12.
- after sleep 1s, i [tid=1098918208] want to try again, iter=13.
- after sleep 1s, i [tid=1098918208] want to try again, iter=14.
- after sleep 1s, i [tid=1098918208] want to try again, iter=15.
- after sleep 1s, i [tid=1098918208] want to try again, iter=16.
- after sleep 1s, i [tid=1098918208] want to try again, iter=17.
- after sleep 1s, i [tid=1098918208] want to try again, iter=18.
- after sleep 1s, i [tid=1098918208] want to try again, iter=19.
- It is my[tid=1098918208] turn, so long i waited...msg=unblock
android run
- @echo "1. build .o file"
-
- @Rem fPIE flag is used in compiling stage.
- D:\android-ndk-r9b-windows-x86\toolchains\arm-linux-androideabi-4.6\prebuilt\windows\bin\arm-linux-androideabi-gcc.exe --sysroot=D:\android-ndk-r9b-windows-x86\platforms\android-13\arch-arm -fPIE -c pt_lock.c
-
- @echo "2. build exec file"
-
- @Rem pie flag is used in linking stage.
- D:\android-ndk-r9b-windows-x86\toolchains\arm-linux-androideabi-4.6\prebuilt\windows\bin\arm-linux-androideabi-gcc.exe --sysroot=D:\android-ndk-r9b-windows-x86\platforms\android-13\arch-arm -pie -o pt_lock pt_lock.o
-
- @pause
里面的gcc和android系统库路径需要根据机器上实际位置修改。
注意android上gcc编译与linux上有点点差别:ndk中gcc不需要需要显式指定-lpthread。可能pthread默认就会链接。android-ndk-r9b-windows-x86\platforms\android-13\arch-arm\usr\lib目录下的这些so加载需要指定。。在Android.mk中类似。
命令行下运行run.cmd,编译pt_lock,然后推到手机上,注意我的nexus4必须是/data/local/tmp下面才有权限,运行后有错误,具体步骤:
- E:\GitHub\ndk_tutorial\pthread_playground>adb shell
- root@mako:/ # cd /data/local/tmp
- cd /data/local/tmp
- root@mako:/data/local/tmp # mv /sdcard/pt_lock ./
- mv /sdcard/pt_lock ./
- root@mako:/data/local/tmp # chmod 751 pt_lock
- chmod 751 pt_lock
- root@mako:/data/local/tmp # ./pt_lock
- error: only position independent executables (PIE) are supported.
报了PIE不支持的错误,n4上安装的是android L系统,gg后知道编译的链接的需要增加pie等设置,参见[ref2],fPIE是编译时候的选项,pie是链接时候的选项,再次重新编译,推到手机上运行OK。。。pt_lock.c不需要做任何修改。
1.线程相关
1)回调函数类型 void* (*pfunc) (void* arg) ,参数通过void*传入,多个参数是通过结构体/数组打包。
2)线程属性,可以设置线程类型,一般是joinable,设置线程栈的大小。如果线程内部要定义大数组一定小心栈越界。
3)线程终止的几种情况:
- 回调函数运行完成,正常退出
- 线程内调用pthread_exit函数,不管是否完成都退出。该函数后面的所有代码都不会被执行(尤其printf等语句)。
- 其他线程显式调用pthread_cancel 结束当前线程。
- 整个进程被终止,因为调用了exit等函数。它下面的所有线程都被杀死,资源被回收。
- main函数创建N个线程,两种做法等待其他线程结束:显式pthread_join等待其他线程结束;main函数中调用pthread_exit,等待其他线程结束。
2. 互斥锁相关
pthread_mutex_init
pthread_mutex_lock,阻塞等待
pthread_mutex_trylock,非阻塞等待
pthread_mutex_destroy
3. 信号量相关
pthread_mutex_init
pthread_mutex_wait 阻塞当前线程,直到满足某些条件时,伪代码如下:
begin
pthread_mutex_unlock( mutex ) 阻塞之前释放互斥锁
block_on_cond( condition ) 条件阻塞
pthread_mutex_lock(mutex) 条件满足后 占有互斥锁,完成工作后需要释放互斥锁
end
pthread_mutex_signal,只有一个线程等待时发送信号量
pthread_mutex_broadcast 多个线程同时等待时使用
pthread_mutex_destroy
4. 生存者/消费者,读写,哲学家进餐模型
refer
1. gcc下面的pie和fPIE 选项标志讲解,http://richardustc./blog/2013/05/pie/
2. android L系统下PIE错误,http://blog.csdn.net/hxdanya/article/details/39371759
3. pthread http:///linux/man-pages/man3/pthread_create.3.html
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