13、iOS底层探索-GCD单例、阻塞使用

语言: CN / TW / HK
时间 2022-06-29 08:15:26

highlight: hybrid

1、单例(dispatch_once)

```swift

ifdef BLOCKS

void dispatch_once(dispatch_once_t *val, dispatch_block_t block) { // 以 val 做为标记是否被执行过 dispatch_once_f(val, block, _dispatch_Block_invoke(block)); }

endif

```

1.1、dispatch_once_f

```swift DISPATCH_NOINLINE void dispatch_once_f(dispatch_once_t val, void ctxt, dispatch_function_t func) { // val 转换为 dispatch_once_gate_t 类型 // 1、执行过的直接返回 dispatch_once_gate_t l = (dispatch_once_gate_t)val;

if !DISPATCH_ONCE_INLINE_FASTPATH || DISPATCH_ONCE_USE_QUIESCENT_COUNTER

uintptr_t v = os_atomic_load(&l->dgo_once, acquire);
if (likely(v == DLOCK_ONCE_DONE)) {
    return;
}

if DISPATCH_ONCE_USE_QUIESCENT_COUNTER

if (likely(DISPATCH_ONCE_IS_GEN(v))) {
    return _dispatch_once_mark_done_if_quiesced(l, v);
}

endif

endif

// 2、没执行过的先进行判断再进行调用
if (_dispatch_once_gate_tryenter(l)) {
    return _dispatch_once_callout(l, ctxt, func);
}
// 3、正在执行的进入等待
return _dispatch_once_wait(l);

} ```

1.2、_dispatch_once_gate_tryenter

swift DISPATCH_ALWAYS_INLINE static inline bool _dispatch_once_gate_tryenter(dispatch_once_gate_t l) { // os_atomic_cmpxchg:原子操作、比较+交换 return os_atomic_cmpxchg(&l->dgo_once, DLOCK_ONCE_UNLOCKED, (uintptr_t)_dispatch_lock_value_for_self(), relaxed); } - DLOCK_ONCE_UNLOCKED代表还未被执行过 - 当 &l->dgo_once 等于 DLOCK_ONCE_UNLOCKED 时将 (uintptr_t)_dispatch_lock_value_for_self() 赋值给 dgo_once 并返回true，否则返回false

1.3、_dispatch_once_callout

swift DISPATCH_NOINLINE static void _dispatch_once_callout(dispatch_once_gate_t l, void *ctxt, dispatch_function_t func) { // 执行方法 _dispatch_client_callout(ctxt, func); // 改变是否执行过的标记 _dispatch_once_gate_broadcast(l); }

```swift DISPATCH_ALWAYS_INLINE static inline void _dispatch_once_gate_broadcast(dispatch_once_gate_t l) { dispatch_lock value_self = _dispatch_lock_value_for_self(); uintptr_t v;

if DISPATCH_ONCE_USE_QUIESCENT_COUNTER

v = _dispatch_once_mark_quiescing(l);

else

// 改变是否执行过的标记
v = _dispatch_once_mark_done(l);

endif

if (likely((dispatch_lock)v == value_self)) return;
_dispatch_gate_broadcast_slow(&l->dgo_gate, (dispatch_lock)v);

} ```

swift DISPATCH_ALWAYS_INLINE static inline uintptr_t _dispatch_once_mark_done(dispatch_once_gate_t dgo) { // 将 &dgo->dgo_once 的值变为 DLOCK_ONCE_DONE return os_atomic_xchg(&dgo->dgo_once, DLOCK_ONCE_DONE, release); }

1.4、_dispatch_once_wait

```swift void _dispatch_once_wait(dispatch_once_gate_t dgo) { dispatch_lock self = _dispatch_lock_value_for_self(); uintptr_t old_v, new_v; dispatch_lock *lock = &dgo->dgo_gate.dgl_lock; uint32_t timeout = 1;

//不断循环
for (;;) {
    //当 &dgo->dgo_once 值变为 DLOCK_ONCE_DONE 跳出循环
    os_atomic_rmw_loop(&dgo->dgo_once, old_v, new_v, relaxed, {
    if (likely(old_v == DLOCK_ONCE_DONE)) {
        os_atomic_rmw_loop_give_up(return);
    }
    ……
    (void)timeout;
}

} ```

小结

主要在 dispatch_once_f 中进行，分为3步： 1. 执行过方法的直接返回 2. 未执行过方法的进行判断，若是 DLOCK_ONCE_UNLOCKED 状态则返回true，然后执行方法并将状态变为 DLOCK_ONCE_DONE 3. 若是正在执行中则进入循环，不停的判断状态，直到状态变成了 DLOCK_ONCE_DONE 退出循环

2、栅栏函数

swift void dispatch_barrier_sync(dispatch_queue_t dq, dispatch_block_t work) { uintptr_t dc_flags = DC_FLAG_BARRIER | DC_FLAG_BLOCK; if (unlikely(_dispatch_block_has_private_data(work))) { return _dispatch_sync_block_with_privdata(dq, work, dc_flags); } // _dispatch_barrier_sync_f _dispatch_barrier_sync_f(dq, work, _dispatch_Block_invoke(work), dc_flags); }

底层流程

我们以同步栅栏函数 dispatch_barrier_sync 为例，整体结构与同步函数高度相似；异步栅栏函数更为复杂，但与同步栅栏函数功能区别就是同步函数与异步函数的区别

2.1、_dispatch_barrier_sync_f

swift DISPATCH_NOINLINE static void _dispatch_barrier_sync_f(dispatch_queue_t dq, void *ctxt, dispatch_function_t func, uintptr_t dc_flags) { _dispatch_barrier_sync_f_inline(dq, ctxt, func, dc_flags); }

2.2、_dispatch_barrier_sync_f_inline

```swift DISPATCH_ALWAYS_INLINE static inline void _dispatch_barrier_sync_f_inline(dispatch_queue_t dq, void *ctxt, dispatch_function_t func, uintptr_t dc_flags) { dispatch_tid tid = _dispatch_tid_self();

if (unlikely(dx_metatype(dq) != _DISPATCH_LANE_TYPE)) {
    DISPATCH_CLIENT_CRASH(0, "Queue type doesn't support dispatch_sync");
}

dispatch_lane_t dl = upcast(dq)._dl;
DISPATCH_ROOT_QUEUE_STATE_INIT_VALUE
if (unlikely(!_dispatch_queue_try_acquire_barrier_sync(dl, tid))) {
    // _dispatch_sync_f_slow 是下断点流程会进入的方法
    return _dispatch_sync_f_slow(dl, ctxt, func, DC_FLAG_BARRIER, dl,
            DC_FLAG_BARRIER | dc_flags);
}

if (unlikely(dl->do_targetq->do_targetq)) {
    return _dispatch_sync_recurse(dl, ctxt, func,
            DC_FLAG_BARRIER | dc_flags);
}
_dispatch_introspection_sync_begin(dl);
_dispatch_lane_barrier_sync_invoke_and_complete(dl, ctxt, func
      DISPATCH_TRACE_ARG(_dispatch_trace_item_sync_push_pop(
                dq, ctxt, func, dc_flags | DC_FLAG_BARRIER)));

} ``` - 通过查看都有哪些方法调用了func参数（即任务block），然后将这些方法打上符号断点，运行后发现走到了 dispatch_sync_f_slow 方法中 - dispatch_sync_f_slow

2.3、dispatch_sync_f_slow

image.png

2.3.1、_dispatch_sync_invoke_and_complete_recurse

swift DISPATCH_NOINLINE static void _dispatch_sync_invoke_and_complete_recurse(dispatch_queue_class_t dq, void *ctxt, dispatch_function_t func, uintptr_t dc_flags DISPATCH_TRACE_ARG(void *dc)) { // 调用方法 _dispatch_sync_function_invoke_inline(dq, ctxt, func); _dispatch_trace_item_complete(dc); // 拔出栅栏,执行后边代码 _dispatch_sync_complete_recurse(dq._dq, NULL, dc_flags); }

  • _dispatch_sync_function_invoke_inline swift DISPATCH_ALWAYS_INLINE static inline void _dispatch_sync_function_invoke_inline(dispatch_queue_class_t dq, void *ctxt, dispatch_function_t func) { dispatch_thread_frame_s dtf; _dispatch_thread_frame_push(&dtf, dq); // 具体调用的方法 _dispatch_client_callout(ctxt, func); _dispatch_perfmon_workitem_inc(); _dispatch_thread_frame_pop(&dtf); }

  • _dispatch_sync_complete_recurse swift DISPATCH_NOINLINE static void _dispatch_sync_complete_recurse(dispatch_queue_t dq, dispatch_queue_t stop_dq, uintptr_t dc_flags) { bool barrier = (dc_flags & DC_FLAG_BARRIER); // do while阻塞线程 do { if (dq == stop_dq) return; if (barrier) { // 有栅栏时通过 dx_wakeup 唤醒后边队列中的任务 dx_wakeup(dq, 0, DISPATCH_WAKEUP_BARRIER_COMPLETE); } else { // 没有栅栏时调用后边代码 _dispatch_lane_non_barrier_complete(upcast(dq)._dl, 0); } dq = dq->do_targetq; barrier = (dq->dq_width == 1); } while (unlikely(dq->do_targetq)); } 唤醒方法由 dx_wakeup 转为 dq_wakeup swift #define dx_wakeup(x, y, z) dx_vtable(x)->dq_wakeup(x, y, z)

    image.png - 上篇GCD中分析异步时也找到过这里（证明了异步操作了线程相关内容），这次看的是 不同的队列类型有不同的唤醒方式

    • _dispatch_root_queue_wakeup swift DISPATCH_NOINLINE void _dispatch_root_queue_wakeup(dispatch_queue_global_t dq, DISPATCH_UNUSED dispatch_qos_t qos, dispatch_wakeup_flags_t flags) { if (!(flags & DISPATCH_WAKEUP_BLOCK_WAIT)) { DISPATCH_INTERNAL_CRASH(dq->dq_priority, "Don't try to wake up or override a root queue"); } if (flags & DISPATCH_WAKEUP_CONSUME_2) { return _dispatch_release_2_tailcall(dq); } }

      • 全局队列的调用的，并没进行栅栏的判断，因此并不会出现阻塞

    • _dispatch_lane_wakeup ```swift DISPATCH_NOINLINE void _dispatch_lane_wakeup(dispatch_lane_class_t dqu, dispatch_qos_t qos, dispatch_wakeup_flags_t flags) { dispatch_queue_wakeup_target_t target = DISPATCH_QUEUE_WAKEUP_NONE;

      if (unlikely(flags & DISPATCH_WAKEUP_BARRIER_COMPLETE)) {
    // 如果执行完栅栏中的任务就调用 _dispatch_lane_barrier_complete 方法进行完成操作
    return _dispatch_lane_barrier_complete(dqu, qos, flags);
}
if (_dispatch_queue_class_probe(dqu)) {
    target = DISPATCH_QUEUE_WAKEUP_TARGET;
}
// 唤醒后边队列中的任务
return _dispatch_queue_wakeup(dqu, qos, flags, target);

      } ``` - 对栅栏中任务的状态进行了判断，从而决定是否唤醒队列中后续任务 image.png - 操作了 waiter，也对队列宽度进行了判断，dq.width == 1时即串行队列 会等待其他任务完成按顺序执行，dq.width > 1时即并发队列 则将栅栏之前的任务执行完成

      小结

      • 栅栏函数针对队列，通过do while阻塞调用队列中后续任务
      • 栅栏函数为什么不阻塞全局并发队列？因为系统也大量使用全局并发队列，如果设计成能阻塞全局并发队列会对系统造成影响
      • 整个流程跳转很多，主要了解一下注释代码的思路即可，调用方法步骤大致如下： image.png

示例

```swift dispatch_queue_t t = dispatch_queue_create("LZ", DISPATCH_QUEUE_CONCURRENT); dispatch_queue_t t2 = dispatch_queue_create("LZ2", DISPATCH_QUEUE_CONCURRENT); dispatch_async(t, ^{ NSLog(@"1"); }); dispatch_barrier_async(t, ^{ sleep(2); NSLog(@"2"); }); dispatch_async(t, ^{ NSLog(@"3"); }); //不同队列 dispatch_async(t2, ^{ NSLog(@"4"); });

//打印结果 14 (睡眠2秒) 23 - `栅栏只能栅住同队列的任务`swift // 稍作修改 1. dispatch_queue_t t = dispatch_queue_create("LZ", DISPATCH_QUEUE_CONCURRENT); 2. dispatch_queue_t t2 = dispatch_queue_create("LZ2", DISPATCH_QUEUE_CONCURRENT); 3. dispatch_async(t, ^{ 4. NSLog(@"1"); 5. }); 6. dispatch_barrier_async(t, ^{ 7. NSLog(@"2"); 8. }); //改为sync 9. dispatch_sync(t, ^{ // 睡眠改为此处 10. sleep(2); 11. NSLog(@"3"); 12. }); 13. dispatch_async(t2, ^{ 14. NSLog(@"4"); 15. });

//打印结果 1 (睡眠2秒) 234 ``` - 即使是不同队列的异步函数，也会被上边的sync卡住读不到内容而导致添加不到队列中 - 9-12行的sync不执行完，不会读到13行的async，因此虽然13-15行有穿越栅栏的能力，但也只能最后执行

3、调度组

  • 与 栅栏函数针对队列 不同，调度组针对 group，类似于引用计数的原理

  • dispatch_group_enter()：进组

  • dispatch_group_leave()：出组

  • dispatch_group_enter() 与 dispatch_group_leave() 需要成对出现

  • dispatch_group_async()：对 dispatch_group_enter() 与 dispatch_group_leave() 进行了封装，更常用的方法 ```swift #ifdef BLOCKS void dispatch_group_async(dispatch_group_t dg, dispatch_queue_t dq, dispatch_block_t db) { dispatch_continuation_t dc = _dispatch_continuation_alloc(); uintptr_t dc_flags = DC_FLAG_CONSUME | DC_FLAG_GROUP_ASYNC; dispatch_qos_t qos;

    qos = _dispatch_continuation_init(dc, dq, db, 0, dc_flags);
_dispatch_continuation_group_async(dg, dq, dc, qos);

    }

    endif

    ``` 文档也有流程说明 image.png

  • dispatch_group_notify()：进出组平衡，计数为0后通知执行

3.1、dispatch_group_enter

```swift void dispatch_group_enter(dispatch_group_t dg) { // The value is decremented on a 32bits wide atomic so that the carry // for the 0 -> -1 transition is not propagated to the upper 32bits.

// os_atomic_sub_orig2o: sub代表将 dg_bits 减1
uint32_t old_bits = os_atomic_sub_orig2o(dg, dg_bits,
        DISPATCH_GROUP_VALUE_INTERVAL, acquire);
uint32_t old_value = old_bits & DISPATCH_GROUP_VALUE_MASK;
if (unlikely(old_value == 0)) {
    _dispatch_retain(dg); // <rdar://problem/22318411>
}
if (unlikely(old_value == DISPATCH_GROUP_VALUE_MAX)) {
        DISPATCH_CLIENT_CRASH(old_bits,
                "Too many nested calls to dispatch_group_enter()");
}

} ``` - dg_bits 本质也是 dg_state - 进组一个任务，将 dg_bits 减 1

3.2、dispatch_group_leave

```swift void dispatch_group_leave(dispatch_group_t dg) { // The value is incremented on a 64bits wide atomic so that the carry for // the -1 -> 0 transition increments the generation atomically.

// os_atomic_add_orig2o: add代表将 dg_state 加1
uint64_t new_state, old_state = os_atomic_add_orig2o(dg, dg_state,
        DISPATCH_GROUP_VALUE_INTERVAL, release);
uint32_t old_value = (uint32_t)(old_state & DISPATCH_GROUP_VALUE_MASK);

if (unlikely(old_value == DISPATCH_GROUP_VALUE_1)) {
    old_state += DISPATCH_GROUP_VALUE_INTERVAL;
do {
    new_state = old_state;
    if ((old_state & DISPATCH_GROUP_VALUE_MASK) == 0) {
        new_state &= ~DISPATCH_GROUP_HAS_WAITERS;
        new_state &= ~DISPATCH_GROUP_HAS_NOTIFS;
    } else {
        // If the group was entered again since the atomic_add above,
        // we can't clear the waiters bit anymore as we don't know for
        // which generation the waiters are for

new_state &= ~DISPATCH_GROUP_HAS_NOTIFS; } if (old_state == new_state) break; } while (unlikely(!os_atomic_cmpxchgv2o(dg, dg_state, old_state, new_state, &old_state, relaxed))); return _dispatch_group_wake(dg, old_state, true); }

if (unlikely(old_value == 0)) {
    DISPATCH_CLIENT_CRASH((uintptr_t)old_value,
            "Unbalanced call to dispatch_group_leave()");
}

} ``` - 出组一个任务，将 dg_state 加 1

3.3、_dispatch_group_notify

image.png

示例

```swift dispatch_group_t g = dispatch_group_create(); dispatch_queue_t t = dispatch_queue_create("LZ", DISPATCH_QUEUE_CONCURRENT); dispatch_queue_t t2 = dispatch_queue_create("LZ2", DISPATCH_QUEUE_CONCURRENT);

// 进组 dispatch_group_enter(g); dispatch_async(t, ^{ sleep(1); NSLog(@"1"); // 出组 dispatch_group_leave(g); });

// 对进出组封装后的简写,更常用 dispatch_group_async(g, t2, ^{ sleep(2); NSLog(@"2"); });

dispatch_group_async(g, dispatch_get_main_queue(), ^{ sleep(3); NSLog(@"3"); });

dispatch_group_async(g, dispatch_get_global_queue(0, 0), ^{ sleep(4); NSLog(@"4"); }); // 出入组平衡后通知执行 dispatch_group_notify(g, dispatch_get_global_queue(0, 0), ^{ NSLog(@"5"); }); ``` - 例中任务都来自不同的队列，依然能按预期阻塞排序成功，说明任务来自哪个队列的调度组并不关心

使用场景

在开发过程中，经常遇到一个页面里面有多个请求，而这多个请求之间还有关联关系。以一个视频播放页面为例，上一级页面传入参数为节目ID，需要从A接口获取视频播放的地址，从B接口获取节目的信息，从C接口获取大数据推荐节目表。需要等这3个接口的数据都回来才能展示UI。 这时候就需要我们的调度组来接受所有任务完成的回调了 ```swift - (void)groupTest01 { dispatch_group_t group = dispatch_group_create(); dispatch_group_enter(group); [self asyncInvoke:^{ NSLog(@"网络请求A回来了"); dispatch_group_leave(group); }]; dispatch_group_enter(group); [self asyncInvoke:^{ NSLog(@"网络请求B回来了"); dispatch_group_leave(group); }];

dispatch_group_enter(group);
[self asyncInvoke:^{
    NSLog(@"网络请求C回来了");
    dispatch_group_leave(group);
}];

dispatch_group_notify(group, dispatch_get_main_queue(), ^{
    NSLog(@"绘制ui");
});

}

//模仿异步执行 - (void)asyncInvoke:(dispatch_block_t)block { dispatch_queue_t queue = dispatch_get_global_queue(0, 0); dispatch_async(queue, block); } ```

小结

  • 与 栅栏函数关注队列 不同 调度组关注group，设置了一个标识dp_state，进组（enter）-1，出组（leave）+1，当任务都执行完毕最后出组后值为0时，此时会立即执行dispatch_group_notify中的任务

  • dispatch_group_enter 与 dispatch_group_leave 必须成对使用；dispatch_group_leave 次数多于 dispatch_group_enter 会导致崩溃；

4、信号量

  • dispatch_semaphore_create：创建信号量，通过指定信号量值的大小可以用来控制并发数

  • dispatch_semaphore_dispose：释放信号量，在出作用域时调用

  • dispatch_semaphore_wait：等待信号量，当信号量的值为0时，阻塞线程一直等待，当信号量的值大于等于1时，对信号量-1

  • dispatch_semaphore_signal：发送信号量，将信号量的值+1

4.1、dispatch_semaphore_create

创建信号量，指定信号量初始值 ```swift dispatch_semaphore_t dispatch_semaphore_create(long value) { dispatch_semaphore_t dsema;

// If the internal value is negative, then the absolute of the value is
// equal to the number of waiting threads. Therefore it is bogus to
// initialize the semaphore with a negative value.
if (value < 0) {
    return DISPATCH_BAD_INPUT;
}

dsema = _dispatch_object_alloc(DISPATCH_VTABLE(semaphore),
sizeof(struct dispatch_semaphore_s));
dsema->do_next = DISPATCH_OBJECT_LISTLESS;
dsema->do_targetq = _dispatch_get_default_queue(false);
// 当前值
dsema->dsema_value = value;
_dispatch_sema4_init(&dsema->dsema_sema, _DSEMA4_POLICY_FIFO);
// 设定值
dsema->dsema_orig = value;
return dsema;

} `` -dsema_value：当前信号量值，后续 **wait、signal** 会改变这个值 -dsema_orig`：设定的信号量初始值

4.2、_dispatch_semaphore_dispose

释放信号量，出作用域时调用，会判断当前信号量是否小于初始信号量，如果小于会引发崩溃，因此 dispatch_semaphore_wait 数量要少于 dispatch_semaphore_signal 的数量，最好成对出现 ```swift void _dispatch_semaphore_dispose(dispatch_object_t dou, DISPATCH_UNUSED bool *allow_free) { dispatch_semaphore_t dsema = dou._dsema; // 若当前信号量 < 初始信号量会抛出报错 if (dsema->dsema_value < dsema->dsema_orig) { DISPATCH_CLIENT_CRASH(dsema->dsema_orig - dsema->dsema_value, "Semaphore object deallocated while in use"); }

_dispatch_sema4_dispose(&dsema->dsema_sema, _DSEMA4_POLICY_FIFO);

} ```

4.3、dispatch_semaphore_wait

信号量阻塞线程 swift long dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout) { // os_atomic_dec2o 进行-1操作 long value = os_atomic_dec2o(dsema, dsema_value, acquire); if (likely(value >= 0)) { // 信号量值>=0不阻塞线程 return 0; } // 阻塞线程方法 return _dispatch_semaphore_wait_slow(dsema, timeout); } - 对信号量的值进行-1操作，得到的 值>=0 的话直接返回，不用进行等待 - _dispatch_semaphore_wait_slow image.png

_dispatch_sema4_wait

swift void _dispatch_sema4_wait(_dispatch_sema4_t *sema) { kern_return_t kr; // 通过do while盲等阻塞线程 do { kr = semaphore_wait(*sema); // 一直等kr,即信号量的值>=0后 } while (kr == KERN_ABORTED); DISPATCH_SEMAPHORE_VERIFY_KR(kr); } - 使用 do while 盲等到信号量的值>=0

4.4、dispatch_semaphore_signal

对信号量当前值+1，若其大于等于0时，dispatch_semaphore_wait 中的 do while 盲等会跳出 swift long dispatch_semaphore_signal(dispatch_semaphore_t dsema) { // os_atomic_inc2o 进行+1操作 long value = os_atomic_inc2o(dsema, dsema_value, release); if (likely(value > 0)) { return 0; } // LONG_MIN 为-1,即是说如果进行了+1操作后值等于-1就抛出错误 if (unlikely(value == LONG_MIN)) { DISPATCH_CLIENT_CRASH(value, "Unbalanced call to dispatch_semaphore_signal()"); } // 创建个 sema4 的同时返回值为1 return _dispatch_semaphore_signal_slow(dsema); }

swift DISPATCH_NOINLINE long _dispatch_semaphore_signal_slow(dispatch_semaphore_t dsema) { _dispatch_sema4_create(&dsema->dsema_sema, _DSEMA4_POLICY_FIFO); _dispatch_sema4_signal(&dsema->dsema_sema, 1); return 1; }

示例

```swift dispatch_semaphore_t sem = dispatch_semaphore_create(0);

dispatch_async(dispatch_get_global_queue(0, 0), ^{ NSLog(@"1"); // 因为创建初始信号量为0,若注释此处会无法打印任何内容 dispatch_semaphore_signal(sem); });

dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER); dispatch_async(dispatch_get_global_queue(0, 0), ^{ sleep(2); NSLog(@"2"); dispatch_semaphore_signal(sem); });

dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER); dispatch_async(dispatch_get_global_queue(0, 0), ^{ NSLog(@"3"); dispatch_semaphore_signal(sem); });

//打印结果 1 (睡眠2秒) 23 ```

小结

  • 信号量初始值可以控制线程池中的最多并发数量
  • 保持线程同步，可以将异步任务转换为同步任务
  • 保证线程安全，为线程加锁，相当于自旋锁

5、dispatch_source

可以监听事件 1487527-f704603d4fa77969.png - dispatch_source_create 创建源 - dispatch_source_set_event_handler 设置源事件回调 - dispatch_source_merge_data 源事件设置数据 - dispatch_source_get_data 获取源事件数据 - dispatch_resume 继续 - dispatch_suspend 挂起 - dispatch_source_cancel 取消源事件

定时器示例

```swift - (void)iTimer { __block int timeout = 60;

dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0);
dispatch_source_set_event_handler(_timer, ^{
    if(timeout <= 0) {
        dispatch_source_cancel(_timer);
    } else {
        timeout--;
        NSLog(@"倒计时:%d", timeout);
    }
});
dispatch_resume(_timer);

} ```

变量增加示例

```swift

import "ViewController.h"

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UIButton iBt; @property (weak, nonatomic) IBOutlet UIProgressView iProgress; @property (nonatomic, strong) dispatch_source_t source; @property (nonatomic, strong) dispatch_queue_t queue; @property (nonatomic, assign) NSUInteger totalComplete; @property (nonatomic ,assign) int iNum;

@end

@implementation ViewController

  • (void)viewDidLoad { [super viewDidLoad];

    self.totalComplete = 0; self.queue = dispatch_queue_create("lg", DISPATCH_QUEUE_SERIAL); self.source = dispatch_source_create(DISPATCH_SOURCE_TYPE_DATA_ADD, 0, 0, dispatch_get_main_queue()); dispatch_source_set_event_handler(self.source, ^{ NSUInteger value = dispatch_source_get_data(self.source); // 每次去获取iNum的值 self.totalComplete += value; NSLog(@"进度: %.2f",self.totalComplete/100.0); self.iProgress.progress = self.totalComplete/100.0; });

// [self iTimer]; }

  • (IBAction)btClick:(id)sender { if ([self.iBt.titleLabel.text isEqualToString:@"开始"]) { dispatch_resume(self.source); NSLog(@"开始了"); self.iNum = 1; [sender setTitle:@"暂停" forState:UIControlStateNormal];
    for (int i= 0; i<1000; i++) {
    dispatch_async(self.queue, ^{
        sleep(1);
        dispatch_source_merge_data(self.source, self.iNum); // 传递iNum触发hander
    });
}

    } else { dispatch_suspend(self.source); NSLog(@"暂停了"); self.iNum = 0; [sender setTitle:@"开始" forState:UIControlStateNormal]; } } @end ```

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