Supply method act 与 tap 之间的区别

Question

在 Raku 文档中关于 Supply 方法 act（相对于 tap） https://docs.raku.org/type/Supply#method_act 表示：

the given code is guaranteed to be executed by only one thread at a time

我的理解是，一个线程必须先完成特定代码对象，然后另一个线程才能运行它。

如果是这样的话，我在尝试实现该功能时偶然发现了不同的行为。看一下下面的代码片段，其中创建了 2 个“行为”并且运行在不同的线程中：

#!/usr/bin/env perl6

say 'Main  runs in [ thread : ', +$*THREAD, ' ]';

my $b = 1;

sub actor {
    print "    Tap_$*tap                             : $^a  ", now;
    
    $*tap < 2 ??
                    do {
                        say " - Sleep 0.1";
                        sleep 0.1
                    }
              !!
                    do {
                        say " - Sleep 0.2";
                        sleep 0.2;
                    }
    
    $b++;
    say "    Tap_$*tap  +1 to $b                     $b  ", now;
}

my $supply = supply {
    for 1..100 -> $i {
        say "For Tap_$*tap [ $i = $i ] => About to emit : $b  ", now;
        emit $b;
        say "For Tap_$*tap [ $i = $i ] =>       Emitted : $b  ", now;
        
        done if $b > 5
    }
}

start {
    my $*tap = 1;
    once say "Tap_$*tap runs in [ thread : {+$*THREAD} ]";
    $supply.act: &actor
}

start {
    my $*tap = 2;
    once say "Tap_$*tap runs in [ thread : {+$*THREAD} ]";
    $supply.act: &actor
}

sleep 1;

结果如下（添加了时间间隔和注释）：

  1   Main  runs in [ thread : 1 ]                                                       - Main thread              
  2   Tap_1 runs in [ thread : 4 ]                                                       - Tap 1 thread             
  3   For Tap_1 [ $i = 1 ] => About to emit : 1  Instant:1603354571.198187               - Supply thread [for tap 1]
  4       Tap_1                             : 1  Instant:1603354571.203074 - Sleep 0.1   - Tap 1 thread             
  5   Tap_2 runs in [ thread : 6 ]                                                       - Tap 2 thread             
  6   For Tap_2 [ $i = 1 ] => About to emit : 1  Instant:1603354571.213826               - Supply thread [for tap 2]
  7       Tap_2                             : 1  Instant:1603354571.213826 - Sleep 0.2   - Tap 2 thread             
  8                                                                                                                 
  9   -----------------------------------------------------------------------------------> Time +0.1 seconds        
 10                                                                                                                 
 11       Tap_1  +1 to $b                     2  Instant:1603354571.305723               - Tap 1 thread             
 12   For Tap_1 [ $i = 1 ] =>       Emitted : 2  Instant:1603354571.305723               - Supply thread [for tap 1]
 13   For Tap_1 [ $i = 2 ] => About to emit : 2  Instant:1603354571.30768                - Supply thread [for tap 1]
 14       Tap_1                             : 2  Instant:1603354571.30768  - Sleep 0.1   - Tap 1 thread             
 15                                                                                                                 
 16   -----------------------------------------------------------------------------------> Time +0.1 seconds        
 17                                                                                                                 
 18       Tap_1  +1 to $b                     3  Instant:1603354571.410354               - Tap 1 thread             
 19   For Tap_1 [ $i = 2 ] =>       Emitted : 4  Instant:1603354571.425018               - Supply thread [for tap 1]
 20       Tap_2  +1 to $b                     4  Instant:1603354571.425018               - Tap 2 thread             
 21   For Tap_1 [ $i = 3 ] => About to emit : 4  Instant:1603354571.425018               - Supply thread [for tap 1]
 22   For Tap_2 [ $i = 1 ] =>       Emitted : 4  Instant:1603354571.425995               - Supply thread [for tap 2]
 23       Tap_1                             : 4  Instant:1603354571.425995 - Sleep 0.1   - Tap 1 thread             
 24   For Tap_2 [ $i = 2 ] => About to emit : 4  Instant:1603354571.425995               - Supply thread [for tap 2]
 25       Tap_2                             : 4  Instant:1603354571.426973 - Sleep 0.2   - Tap 2 thread             
 26                                                                                                                 
 27   -----------------------------------------------------------------------------------> Time +0.1 seconds        
 28                                                                                                                 
 29       Tap_1  +1 to $b                     5  Instant:1603354571.528079               - Tap 1 thread             
 30   For Tap_1 [ $i = 3 ] =>       Emitted : 5  Instant:1603354571.52906                - Supply thread [for tap 1]
 31   For Tap_1 [ $i = 4 ] => About to emit : 5  Instant:1603354571.52906                - Supply thread [for tap 1]
 32       Tap_1                             : 5  Instant:1603354571.53004  - Sleep 0.1   - Tap 1 thread             
 33                                                                                                                 
 34   -----------------------------------------------------------------------------------> Time +0.1 seconds        
 35                                                                                                                 
 36       Tap_2  +1 to $b                     6  Instant:1603354571.62859                - Tap 2 thread             
 37   For Tap_2 [ $i = 2 ] =>       Emitted : 6  Instant:1603354571.62859                - Supply thread [for tap 2]
 38       Tap_1  +1 to $b                     7  Instant:1603354571.631512               - Tap 1 thread             
 39   For Tap_1 [ $i = 4 ] =>       Emitted : 7  Instant:1603354571.631512               - Supply thread [for tap 2]

可以很容易地观察到代码对象（子例程 &actor）在 2 个线程中并发运行ning（例如，参见输出行 4 和 7）。

谁能澄清我对此事的误解？

Answer 1

在 Raku 的日常使用中，tap 和 act 之间几乎没有任何区别，因为您遇到的几乎每个 Supply 都是 串行电源。串行供应是一种已经强制执行协议的供应，即在处理完前一个值之前不会发出一个值。 act的实现是：

method act(Supply:D: &actor, *%others) {
    self.sanitize.tap(&actor, |%others)
}

其中 sanitize 强制值的连续发射，此外确保事件遵循语法 emit* [done | quit]。由于这些属性通常是非常需要的，每个 built-in 获得 Supply 的方法都提供了它们，除了能够创建 Supplier 并在其上调用 unsanitized-supply . （历史记录：一个非常早期的原型并没有如此广泛地强制执行这些属性，因此更需要一种方法来完成 act 所做的事情。虽然随着设计涉及到最终交付的内容，对它的需求减少了第一个语言版本，它必须保留其漂亮的简称。）

产生误解的原因是期望事件的序列化是 每个源，而实际上它是 每个订阅。考虑这个例子：

my $timer = Supply.interval(1);
$timer.tap: { say "A: {now}" };
$timer.tap: { say "B: {now}" };
sleep 5;

产生这样的输出：

A: Instant:1603364746.02766
B: Instant:1603364746.031255
A: Instant:1603364747.025255
B: Instant:1603364747.028305
A: Instant:1603364748.025584
B: Instant:1603364748.029797
A: Instant:1603364749.026596
B: Instant:1603364749.029643
A: Instant:1603364750.027881
B: Instant:1603364750.030851
A: Instant:1603364751.030137

事件源只有一个，但我们为其建立了两个订阅。每个订阅都强制执行序列规则，所以如果我们这样做：

my $timer = Supply.interval(1);
$timer.tap: { sleep 1.5; say "A: {now}" };
$timer.tap: { sleep 1.5; say "B: {now}" };
sleep 5;

然后我们观察到如下输出：

A: Instant:1603364909.442341
B: Instant:1603364909.481506
A: Instant:1603364910.950359
B: Instant:1603364910.982771
A: Instant:1603364912.451916
B: Instant:1603364912.485064

显示每个订阅一次获得一个事件，但仅仅共享一个 (on-demand) 源不会产生任何共享背压。

由于并发控制与订阅关联，如果将相同的闭包克隆传递给 tap/act 则无关紧要。跨多个订阅实施并发控制是 supply/react/whenever 的领域。例如：

my $timer = Supply.interval(1);
react {
    whenever $timer {
        sleep 1.5;
        say "A: {now}"
    }
    whenever $timer {
        sleep 1.5;
        say "B: {now}"
    }
}

给出这样的输出：

A: Instant:1603365363.872672
B: Instant:1603365365.379991
A: Instant:1603365366.882114
B: Instant:1603365368.383392
A: Instant:1603365369.884608
B: Instant:1603365371.386087

由于 react 块隐含的并发控制，每个事件相隔 1.5 秒。

Supply method act 与 tap 之间的区别

Difference between Supply method act vs tap

tap

act

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