android中库bionic线程函数pthread_create的具体执行流程

android中库bionic线程函数pthread_create的具体执行流程

int pthread_create(pthread_t *thread_out, pthread_attr_t const * attr,

                   void *(*start_routine)(void *), void * arg)

{

......

    // Create a mutex for the thread in TLS_SLOT_SELF to wait on once it starts so we can keep

    // it from doing anything until after we notify the debugger about it

    start_mutex = (pthread_mutex_t *) &tls[TLS_SLOT_SELF];

    pthread_mutex_init(start_mutex, NULL); // 初始化thread启动锁

    pthread_mutex_lock(start_mutex); // 获取thread的启动锁,clone返回

// 之后下面的__thread_entryh函数将因为调用pthread_mutex_lock(start_mutex);而被pending

// 直到pthread_create函数退出时调用下面第10行的pthread_mutex_unlock(start_mutex);解锁

// 函数,__thread_entryh函数才能获取启动锁，进而开始执行start_routine函数

// 所以我们可以看到函数pthread_create一旦返回，线程即开始自动执行[luther.gliethttp]

    tls[TLS_SLOT_THREAD_ID] = thread;

    tid = __pthread_clone((int(*)(void*))start_routine, tls,

                CLONE_FILES | CLONE_FS | CLONE_VM | CLONE_SIGHAND

                | CLONE_THREAD | CLONE_SYSVSEM | CLONE_DETACHED,

                arg); // 调用__pthread_clone函数swi陷入内核让内核执行实际clone操作

......

    // Let the thread do it's thing

    pthread_mutex_unlock(start_mutex); // pthread_create函数执行完毕,

// 那么我们在这里释放启动锁，这样下面的__thread_entry将获取到启动锁而

// 正常启动pthread_create函数传入的参数处理函数start_routine[luther.gliethttp]

    *thread_out = (pthread_t)thread;

    return 0;

}

==> __pthread_clone该函数位于bionic/libc/arch-arm/bionic/clone.S

    .text

    .type __pthread_clone, #function

    .global __pthread_clone

    .align 4

__pthread_clone:

......

#if __ARM_EABI__

    stmfd   sp!, {r4, r7}

    ldr     r7, =__NR_clone

    swi     #0 swi软中断陷入内核,让内核执行clone操作

#else

    swi     #__NR_clone

#endif

......

b       __thread_entry swi返回之后执行该函数

......

==> __thread_entry该函数位于bionic/libc/bionic/pthread.c

/*

 * This trampoline is called from the assembly clone() function

 */

void __thread_entry(int (*func)(void*), void *arg, void **tls)

{

    int retValue;

    pthread_internal_t * thrInfo;

    // Wait for our creating thread to release us. This lets it have time to

    // notify gdb about this thread before it starts doing anything.

    pthread_mutex_t * start_mutex = (pthread_mutex_t *)&tls[TLS_SLOT_SELF];

    pthread_mutex_lock(start_mutex); // 直到pthread_create函数

// 退出时执行pthread_mutex_unlock(start_mutex);这里的启动锁才能正常获取到,进而该线程

// 开始继续执行下面的操作,完成正常启动工作[luther.gliethttp]

    pthread_mutex_destroy(start_mutex);

    thrInfo = (pthread_internal_t *) tls[TLS_SLOT_THREAD_ID];

    __init_tls( tls, thrInfo );

    pthread_exit( (void*)func(arg) );

}