在Rust單元測驗工具中，我如何等待回呼被呼叫？

請考慮以下功能：

pub fn shiny_function(&mut self, cb: Arc<Mutex<dyn FnMut(usize)   Send>>) {
    // Do stuff here...
}

現在，問題是，我如何撰寫一個單元測驗來檢查回呼（閉包）引數是否等于某個值？

顯而易見的解決方案如下所示：

#[test]
fn progress_cb() {
    let cut = ... // cut stands for Class Under Test
    cut.shiny_function(Arc::new(Mutex::new(move |percent| {
        // Assert here maybe? I don't know.
    })));

    cut.shiny_function();

    // Or maybe assert it somehow here? I don't know.
}

但問題是測驗甚至在回呼被呼叫之前就完成了。我如何告訴測驗工具等到回呼被呼叫？

uj5u.com熱心網友回復：

您可以使用標準庫中提供的常規并發結構來解決此問題。在這個例子中，我使用了一個屏障來確保在測驗函式退出之前到達閉包的末尾。我創建值為 2 的屏障，因為在兩個執行緒上釋放屏障之前必須呼叫兩次等待。shiny_function多次呼叫時可能不希望出現這種行為，因此您還可以替換另一個僅在單個位置阻塞的并發結構。

use std::sync::{Arc, Barrier};

#[test]
fn progress_cb() {
    let cut = ... // cut stands for Class Under Test

    // Create a barrier for this thread and clone it to move into the closure
    let barrier = Arc::new(Barrier::new(2));
    let barrier_clone = barrier.clone();

    cut.shiny_function(Arc::new(Mutex::new(move |percent| {
        // Perform tests
        assert_eq!(percent, foo);

        // Once we finish we can trigger the barrier so the outer thread can continue
        barrier_clone.wait();
    })));

    // Don't exit the function until the barrier has been resolved in the callback
    barrier.wait();
}

編輯：shiny_function如果由于每次呼叫的閉包阻塞并在單個測驗函式中阻止以后的呼叫，障礙開始成為問題，您可以使用這里的結構。

use std::sync::{Arc, Mutex, Condvar};

pub struct SingleBlockingBarrier {
    target: u32,
    counter: Mutex<u32>,
    lock: Condvar,
}

impl SingleBlockingBarrier {
    pub fn new(target: u32) -> Arc<Self> {
        Arc::new(SingleBlockingBarrier {
            target,
            counter: Mutex::new(0),
            lock: Condvar::new(),
        })
    }

    pub fn signal(&self) {
        let mut guard = self.counter.lock().unwrap();
        *guard  = 1;
        if *guard >= self.target {
            self.lock.notify_all();
        }
    }

    // Block until signal has been called the target number of times
    pub fn block_until_finished(&self) {
        let mut guard = self.counter.lock().unwrap();
        
        loop {
            if *guard >= self.target {
                return;
            }

            guard = self.lock.wait(guard).unwrap();
        }
    }
}

#[test]
fn progress_cb() {
    let cut = ... // cut stands for Class Under Test

    // Create a barrier for this thread and clone it to move into the closure
    let barrier = SingleBlockingBarrier::new(10);

    for _ in 0..10 {
        let barrier_clone = barrier.clone();

        cut.shiny_function(Arc::new(Mutex::new(move |percent| {
            // Perform tests
            assert_eq!(percent, foo);
    
            // Notify barrier that a worker has finished without blocking
            barrier_clone.signal();
        })));
    }

    // Block until all non-blocking barriers have been reached
    barrier.block_until_finished();
}

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