说明

thread封装了pthread, 完成的功能是, 使用fixed_queue作为workquque, 将需要被执行的thread function放入其中(enqueue), 使用thread_post来enqueue,enqueue完成后semophore发送信号给dequeue, 然后使用reactor中的epoll_wait监控到dequeue semaphore变更, 就读出queue中的数据, 而queue中的item是thread function与args, 于是运行这个function, 完成任务执行功能. 

结构体

struct thread_t {   bool is_joined;  pthread_t pthread;  pid_t tid;  char name[THREAD_NAME_MAX + 1];   reactor_t *reactor;        // 对dequeue semophore fd进行监听  fixed_queue_t *work_queue; //存放work_item};struct start_arg {   thread_t *thread;  semaphore_t *start_sem;  int error;};typedef struct { //用于thread_post传递需要的执行的function以及function需要的args  thread_fn func;   void *context;} work_item_t;
函数分析
创建thread以及reactor
thread_t *thread_new_sized(const char *name, size_t work_queue_capacity) {  assert(name != NULL);  assert(work_queue_capacity != 0);  thread_t *ret = osi_calloc(sizeof(thread_t));  if (!ret)    goto error;  ret->reactor = reactor_new();   if (!ret->reactor)    goto error;  ret->work_queue = fixed_queue_new(work_queue_capacity);  if (!ret->work_queue)    goto error;  // Start is on the stack, but we use a semaphore, so it's safe  struct start_arg start;  start.start_sem = semaphore_new(0);  if (!start.start_sem)    goto error;  strncpy(ret->name, name, THREAD_NAME_MAX);   start.thread = ret;  start.error = 0;  pthread_create(&ret->pthread, NULL, run_thread, &start);  semaphore_wait(start.start_sem); // A1:等待run_thread执行后,且使用PRctl更改名字成功才返回
等待thread_post中进行唤醒才会退出,在那之前包装pthread_create创建出来的thread function可以一直执行, 这里返回即为主线程的退出  semaphore_free(start.start_sem);  if (start.error) //error值在run_pthread中设置的,见下面的B1    goto error;  return ret;error:;  if (ret) {    fixed_queue_free(ret->work_queue, osi_free);    reactor_free(ret->reactor);  }  osi_free(ret);  return NULL;}
thread_post
完成thread的main_loop函数设置
bool thread_post(thread_t *thread, thread_fn func, void *context) {  assert(thread != NULL);  assert(func != NULL);  // TODO(sharvil): if the current thread == |thread| and we've run out  // of queue space, we should abort this Operation, otherwise we'll  // deadlock.  // Queue item is freed either when the queue itself is destroyed  // or when the item is removed from the queue for dispatch.  work_item_t *item = (work_item_t *)osi_malloc(sizeof(work_item_t));  if (!item) {    LOG_ERROR("%s unable to allocate memory: %s", __func__, strerror(errno));    return false;  }  item->func = func; //设置回调函数  item->context = context;  fixed_queue_enqueue(thread->work_queue, item);//A4: enqueue后dequeue的semophore会从epoll_wait中回来, 然后就会去dequeue.对应B4  return true;}
run_thread阻塞等待poll_wait
static void *run_thread(void *start_arg) {  assert(start_arg != NULL);  struct start_arg *start = start_arg;  thread_t *thread = start->thread;  assert(thread != NULL);  if (prctl(PR_SET_NAME, (unsigned long)thread->name) == -1) {    LOG_ERROR("%s unable to set thread name: %s", __func__, strerror(errno));    start->error = errno;  // B1:设置thread name失败    semaphore_post(start->start_sem);//B2:设置好了error变量可以让new_thread返回退出了.    return NULL;  }  thread->tid = gettid();  semaphore_post(start->start_sem); //B3: 同B2  int fd = fixed_queue_get_dequeue_fd(thread->work_queue);   void *context = thread->work_queue;  reactor_object_t *work_queue_object = reactor_register(thread->reactor, fd, context, work_queue_read_cb, NULL);//B4:注意里面fd是dequeue的fd,因此在enqueue后actor会执行workqueue_read_cb读取queue的数据进行处理  reactor_start(thread->reactor); //B5: poll_wait,等待enqueue来唤醒自己,在没有enqueue之前都是休眠,有了enqueue就是有需要执行的任务(item->func)需要执行了.  reactor_unregister(work_queue_object);  // Make sure we dispatch all queued work items before exiting the thread.  // This allows a caller to safely tear down by enqueuing a teardown  // work item and then joining the thread.  size_t count = 0;  work_item_t *item = fixed_queue_try_dequeue(thread->work_queue);  while (item && count <= fixed_queue_capacity(thread->work_queue)) {    item->func(item->context); //取出callback函数进行执行    osi_free(item);    item = fixed_queue_try_dequeue(thread->work_queue);//逐个取出    ++count;   }  if (count > fixed_queue_capacity(thread->work_queue))    LOG_DEBUG("%s growing event queue on shutdown.", __func__);  return NULL;}
使用
下面以hci_layer.c中的thread为例说明一下使用.
1. 使用thread_new创建thread
这里仅仅传入thread name:
  thread = thread_new("hci_thread");  if (!thread) {    LOG_ERROR("%s unable to create thread.", __func__);    goto error;  }这里面静默创建了reactor与fixed_queue. 
2. 使用thread_post注册thread需要处理的function,即enqueue item function,然后唤醒run_thread dequeue来执行
下面这个就是event_finish_startup为需要执行的函数
  thread_post(thread, event_finish_startup, NULL);
这个注册的函数定义如下, 这里面可以看到调用到了HAL层的open, 即libbt-vendor.so中的open, 在switch中的"case BT_VND_OP_USERIAL_OPEN".
static void event_finish_startup(UNUSED_ATTR void *context) {  LOG_INFO("%s", __func__);  hal->open();  vendor->send_async_command(VENDOR_CONFIGURE_FIRMWARE, NULL);}
对于case BT_VND_OP_USERIAL_OPEN, 可以查看文件hardware/broadcom/libbt/src/bt_vendor_brcm.c中的代码, 这里面调用到了硬件操作, 例如:
        case BT_VND_OP_USERIAL_OPEN:            {                int (*fd_array)[] = (int (*)[]) param;                int fd, idx;                ALOGW("--------- BT_VND_OP_USERIAL_OPEN Done ------------");                fd = userial_vendor_open((tUSERIAL_CFG *) &userial_init_cfg); //Open硬件操作                if (fd != -1)                {                    for (idx=0; idx < CH_MAX; idx++)                        (*fd_array)[idx] = fd;                    retval = 1;                }                /* retval contains numbers of open fd of HCI channels */            }            break;dequeue取出后执行这个函数, 然后返回.