thread-safety - Lock.protect和callame

Question

我正在尝试自动编写一个特征以对sub进行线程安全。这就是我得到的:

#| A trait to ensure that a sub is not run on multiple threads simultaneously.
multi sub trait_mod:<is> (Sub \code, :$protected!) {

    # If :!protected, do nothing.
    if $protected {

        # Create a new lock outside the multithreaded area
        my $lock = Lock.new;

        # Wrap the sub with a routine that hides callsame in a lock
        code.wrap: sub (|) {
            $lock.protect: {callsame}
        }
    }
}

#| Should print "Start X and finish X" if properly protected
sub needs-protection($x) is protected {
   print "Start $x and ";
   sleep 1;
   say "finish $x";
}

# Test it out.
# If not protected, completes in 1 second with malformed output
(1..4).hyper(:1batch, :4degree) { 
   needs-protection $_
}

但是，对于AFAICT，似乎 callsame没有做任何事情(它返回 Nil就是这样)。我的猜测是，它以某种方式尝试调用 .protect的其他候选对象，但我没有看到一种方法来确保 callsame链接到包装的子对象，而不是其他方法。
我能够做到这一点

multi sub trait_mod:<is> (Sub \code, :$protected!) {
    if $protected {
        my $lock = Lock.new;
        code.wrap: sub (|c) {
            if CALLERS::<$*PROTECTED> {
                $*PROTECTED = False;
                return callsame;
            }

            $lock.protect: { 
                my $*PROTECTED = True;
                code.CALL-ME(|c);
            }
        }
    }
}

但这感觉很笨拙，我可能丢失了一些东西，当事情不安全时，允许 True的 $*PROTECTED值滑出。有没有办法在 callsame编码的块内制作直接的 protect？

Answer 1

像callsame这样的延迟例程会寻找最近的动态范围内的调度来恢复。传递给{callsame}方法的protect块将由protect方法调用，动态范围内最近的调度将是分配给protect的方法。因此，它将尝试遵循protect的基类中的Lock方法。没有，因此是Nil结果。
为了解决这个问题，我们需要在正确的动态范围内获取包装的目标，并使其在词法上可用。这可以使用nextcallee实现:

#| A trait to ensure that a sub is not run on multiple threads simultaneously.
multi sub trait_mod:<is> (Sub \code, :$protected!) {
    # If :!protected, do nothing.
    if $protected {

        # Create a new lock outside the multithreaded area
        my $lock = Lock.new;

        # Wrap the sub with a routine that hides callsame in a lock
        code.wrap: sub (|c) {
            my &target = nextcallee;
            $lock.protect: { target(|c) }
        }
    }
}

#| Should print "Start X and finish X" if properly protected
sub needs-protection($x) is protected {
   print "Start $x and ";
   sleep 1;
   say "finish $x";
}

# Test it out.
# If not protected, completes in 1 second with malformed output
for (1..4).hyper(:1batch, :4degree) { 
   needs-protection $_
}

这给出了我期望的输出。