v/vlib/sync/once.v

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module sync
import sync.stdatomic
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pub struct Once {
mut:
m RwMutex
pub:
count u64
}
// new_once return a new Once struct.
pub fn new_once() &Once {
mut once := &Once{}
once.m.init()
return once
}
// do executes the function `f()` only once
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pub fn (mut o Once) do(f fn ()) {
if stdatomic.load_u64(&o.count) < 1 {
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o.do_slow(f)
}
}
fn (mut o Once) do_slow(f fn ()) {
o.m.@lock()
if o.count < 1 {
stdatomic.store_u64(&o.count, 1)
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f()
}
o.m.unlock()
}
// do_with_param executes `f(param)` only once`
// This method can be used as a workaround for passing closures to once.do/1 on Windows
// (they are not implemented there yet) - just pass your data explicitly.
// i.e. instead of:
// ```v
// once.do(fn [mut o] () {
// o.add(5)
// })
// ```
// ... you can use:
// ```v
// once.do_with_param(fn (mut o One) {
// o.add(5)
// }, o)
// ```
pub fn (mut o Once) do_with_param(f fn (voidptr), param voidptr) {
if stdatomic.load_u64(&o.count) < 1 {
o.do_slow_with_param(f, param)
}
}
fn (mut o Once) do_slow_with_param(f fn (p voidptr), param voidptr) {
o.m.@lock()
if o.count < 1 {
stdatomic.store_u64(&o.count, 1)
f(param)
}
o.m.unlock()
}