Documentation for sub atomic-fetch assembled from the following types:

class Scalar

From Scalar

(Scalar) sub atomic-fetch

multi sub atomic-fetch($target is rw)

Performs an atomic read of the value in the Scalar $target and returns the read value. Using this routine instead of simply using the variable ensures that the latest update to the variable from other threads will be seen, both by doing any required hardware barriers and also preventing the compiler from lifting reads. For example:

my $started = False;
start { atomic-assign($started, True) }
until atomic-fetch($started) { }

Is certain to terminate, while in:

my $started = False;
start { atomic-assign($started, True) }
until $started { }

It would be legal for a compiler to observe that $started is not updated in the loop, and so lift the read out of the loop, thus causing the program to never terminate.

class atomicint

From atomicint

(atomicint) sub atomic-fetch

Defined as:

multi sub atomic-fetch(atomicint $ is rw)

Performs an atomic read of a native integer, which may live in a lexical, attribute, or native array element. Using this routine instead of simply using the variable ensures that the latest update to the variable from other threads will be seen, both by doing any required hardware barriers and also preventing the compiler from lifting reads. For example:

my atomicint $i = 0;
start { atomic-assign($i, 1) }
while atomic-fetch($i) == 0 { }

Is certain to terminate, while in:

my atomicint $i = 0;
start { atomic-assign($i, 1) }
while $i == 0 { }

It would be legal for a compiler to observe that $i is not updated in the loop, and so lift the read out of the loop, thus causing the program to never terminate.