小记——linux线程

linux线程标准是POSIX threads, 也就是著名的 Pthreads。

Pthreads实现于glibc库中，分别有两个版本：LinuxThreads和Native POSIX Thread Library (NPTL) 。libc2.6后包含了NPTL。后续版本是NGPL(Next Generation POSIX Threads)。

现在一般说的linux线程多指NPTL版本，本文也只讨论NPTL版本的线程及其相关API。

头文件#include <pthread.h>

APIS:

1. 创建线程

int pthread_create (pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void *), void *arg);

Upon successful invocation, a new thread is created and begins executing the function provided by start_routine, passed the sole argument arg.

线程创建API的特别之处在于其失败时并不设置errno。下面是示例代码：

pthread_t tread;int ret;ret = pthread_create (&thread, NULL, start_routine, NULL);if (!ret) {errno = ret;perror("pthread_create");return -1;}

2. 获得自身线程

pthread_t pthread_self (void);

Usage is simple, because the function cannot fail
3. 线程相等性判断

int pthread_equal (pthread_t t1, pthread_t t2);

通过线程ID来判断其相等性，相等则返回非零

4. 线程本身退出

Threads may terminate under several circumstances, all of which have analogues to process termination:
• If a thread returns from its start routine, it terminates. This is akin to “falling off the end” of main().
• If a thread invokes the pthread_exit() function (discussed subsequently), it terminates. This is akin to calling exit().
• If the thread is canceled by another thread via the pthread_cancel() function, it terminates. This is akin to being sent the SIGKILL signal via kill().

4.1 结束自己

void pthread_exit (void *retval);

4.2 结束其它线程

int pthread_cancel (pthread_t thread);

该函数会阻塞直到指定的线程结束，当指定的线程是不可被其它线程结束时，该函数会一直阻塞。

一个线程可以设置为可被其它线程结束和不可被其它线程结束，缺省为可以被其它线程结束。

4.2.1

int pthread_setcancelstate (int state, int *oldstate);

设置线程可被其它线程结束与否

state may be PTHREAD_CANCEL_ENABLE or PTHREAD_CANCEL_DISABLE, to enable or disable cancellation, respectively.

4.2.2

int pthread_setcanceltype (int type, int *oldtype);

设置结束类型：异步或者延迟

type may be PTHREAD_CANCEL_ASYNCHRONOUS or PTHREAD_CANCEL_DEFERRED, to use asynchronous or deferred cancellation, respectively

5. 等待线程结束

int pthread_join (pthread_t thread, void **retval);

如果等待的线程已经结束，函数将立刻返回。

Once thread terminates, the invoking thread is woken up and, if retval is not NULL, provided the return value the terminated thread passed to pthread_exit() or returned from its start routine. 

6. 分离线程

int pthread_detach (pthread_t thread);

对于不希望join的线程，可将其detach.

On success, pthread_detach() detaches the thread specified by thread and returns zero. Results are undefined if you call pthread_detach() on a thread that is already detached. On error, the function returns ESRCH indicating that thread is invalid.
EXAMPLE:

#include <stdlib.h>#include <stdio.h>#include <pthread.h>void * start_thread (void *message){printf ("%s\n", (const char *) message);return message;}int main (void){pthread_t thing1, thing2;const char *message1 = "Thing 1";const char *message2 = "Thing 2";/* Create two threads, each with a different message. */pthread_create (&thing1, NULL, start_thread, (void *) message1);pthread_create (&thing2, NULL, start_thread, (void *) message2);/** Wait for the threads to exit. If we didn't join here,* we'd risk terminating this main thread before the* other two threads finished.*/pthread_join (thing1, NULL);pthread_join (thing2, NULL);return 0;}

7. 互斥变量（Pthread Mutexes）

互斥变量仅仅能被一个线程使用。

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;int pthread_mutex_lock (pthread_mutex_t *mutex);int pthread_mutex_unlock (pthread_mutex_t *mutex);

实现局部锁：

class ScopedMutex {public:ScopedMutex (pthread_mutex_t& mutex):mutex_ (mutex){    pthread_mutex_lock (&mutex_);} ~ScopedMutex (){    pthread_mutex_unlock (&mutex_);}private:    pthread_mutex_t& mutex_;};