61 lines
1.7 KiB
V
61 lines
1.7 KiB
V
// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
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// Use of this source code is governed by an MIT license
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// that can be found in the LICENSE file.
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module sync
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[trusted]
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fn C.atomic_fetch_add_u32(voidptr, u32) u32
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// WaitGroup
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// Do not copy an instance of WaitGroup, use a ref instead.
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//
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// usage: in main thread:
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// `wg := sync.new_waitgroup()
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// `wg.add(nr_jobs)` before starting jobs with `go ...`
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// `wg.wait()` to wait for all jobs to have finished
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//
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// in each parallel job:
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// `wg.done()` when finished
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//
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// [init_with=new_waitgroup] // TODO: implement support for init_with struct attribute, and disallow WaitGroup{} from outside the sync.new_waitgroup() function.
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[heap]
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struct WaitGroup {
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mut:
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task_count u32 // current task count - reading/writing should be atomic
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sem Semaphore // This blocks wait() until tast_countreleased by add()
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}
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pub fn new_waitgroup() &WaitGroup {
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mut wg := &WaitGroup{}
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wg.init()
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return wg
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}
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pub fn (mut wg WaitGroup) init() {
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wg.sem.init(0)
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}
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// add increments (+ve delta) or decrements (-ve delta) task count by delta
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// and unblocks any wait() calls if task count becomes zero.
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// add panics if task count drops below zero.
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pub fn (mut wg WaitGroup) add(delta int) {
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old_nrjobs := int(C.atomic_fetch_add_u32(&wg.task_count, u32(delta)))
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new_nrjobs := old_nrjobs + delta
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if new_nrjobs < 0 {
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panic('Negative number of jobs in waitgroup')
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}
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if new_nrjobs == 0 {
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wg.sem.post()
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}
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}
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// done is a convenience fn for add(-1)
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pub fn (mut wg WaitGroup) done() {
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wg.add(-1)
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}
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// wait blocks until all tasks are done (task count becomes zero)
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pub fn (mut wg WaitGroup) wait() {
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wg.sem.wait() // blocks until task_count becomes 0
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}
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