暫停和恢復輔助，同步線程

Question

使用DispatchQueue，我可以創造一個新的線程，我可以與主線程同步或異步運行：

import Foundation 

let thread = DispatchQueue(label: "thread") 

thread.sync { 
    // Code here... 
} 

我一直在努力做的是運行單獨的線程到某個點，暫停它，繼續運行主線程，然後返回輔助線程。那可能嗎？

這裏有一個例子：

import Foundation 

let thread = DispatchQueue(label: "thread") 

thread.sync { 
    print("Thread Started") 
    // Pause Thread 
    print("Thread Ended") 
} 
print("Before Thread Ended") 
// Start Thread 
print("After Thread Ended") 

所需的輸出：

Thread Started 
Before Thread Ended 
Thread Ended 
After Thread Ended 

Answer 1

我以前也有過類似的問題 - 你可以使用dispatch_semaphore暫停和恢復線程。

dispatch_semaphore_wait遞減具有默認值爲0的信號，你可以指定你想要多少時間就需要等待包括DISPATCH_TIME_FOREVER和dispatch_semaphore_signal增加它的值返回到0，然後繼續你的線程。希望有所幫助！

例（你可以嘗試在操場這段代碼）：

// Main thread 
let semaphore = DispatchSemaphore(value:0) 
let queue = DispatchQueue(label: "Queue") 

//Asynchronously execute some code on a separate thread 
queue.async { 
    print("Code executed before pause") 

    // This will pause the thread 
    semaphore.wait(timeout: .distantFuture) 

    print("Woohoo - Code executed after resuming the semaphore") 
} 

// Some sort of trigger - I am putting the thread to sleep for 5 sec as next line will otherwise execute straight away  
sleep(5) 

// On main thread resume the semaphore 
semaphore.signal()