v/vlib/context/cancel_test.v

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// vtest retry: 3
import context
// This example demonstrates the use of a cancelable context to prevent a
// routine leak. By the end of the example function, the routine started
// by gen will return without leaking.
fn test_with_cancel() {
// gen generates integers in a separate routine and
// sends them to the returned channel.
// The callers of gen need to cancel the context once
// they are done consuming generated integers not to leak
// the internal routine started by gen.
gen := fn (mut ctx context.Context) chan int {
dst := chan int{}
go fn (mut ctx context.Context, dst chan int) {
mut v := 0
ch := ctx.done()
for {
select {
_ := <-ch {
// returning not to leak the routine
return
}
dst <- v {
v++
}
}
}
}(mut ctx, dst)
return dst
}
mut background := context.background()
mut ctx, cancel := context.with_cancel(mut &background)
defer {
cancel()
}
mut mut_ctx := ctx
mut ctx2 := &mut_ctx
ch := gen(mut ctx2)
for i in 0 .. 5 {
v := <-ch
assert i == v
}
}