85 lines
2.3 KiB
V
85 lines
2.3 KiB
V
// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
|
|
// Use of this source code is governed by an MIT license
|
|
// that can be found in the LICENSE file.
|
|
module sync
|
|
|
|
[trusted]
|
|
fn C.atomic_fetch_add_u32(voidptr, u32) u32
|
|
|
|
[trusted]
|
|
fn C.atomic_load_u32(voidptr) u32
|
|
|
|
[trusted]
|
|
fn C.atomic_compare_exchange_weak_u32(voidptr, voidptr, u32) bool
|
|
|
|
// WaitGroup
|
|
// Do not copy an instance of WaitGroup, use a ref instead.
|
|
//
|
|
// usage: in main thread:
|
|
// `wg := sync.new_waitgroup()
|
|
// `wg.add(nr_jobs)` before starting jobs with `go ...`
|
|
// `wg.wait()` to wait for all jobs to have finished
|
|
//
|
|
// in each parallel job:
|
|
// `wg.done()` when finished
|
|
//
|
|
// [init_with=new_waitgroup] // TODO: implement support for init_with struct attribute, and disallow WaitGroup{} from outside the sync.new_waitgroup() function.
|
|
[heap]
|
|
pub struct WaitGroup {
|
|
mut:
|
|
task_count u32 // current task count - reading/writing should be atomic
|
|
wait_count u32 // current wait count - reading/writing should be atomic
|
|
sem Semaphore // This blocks wait() until tast_countreleased by add()
|
|
}
|
|
|
|
pub fn new_waitgroup() &WaitGroup {
|
|
mut wg := WaitGroup{}
|
|
wg.init()
|
|
return &wg
|
|
}
|
|
|
|
pub fn (mut wg WaitGroup) init() {
|
|
wg.sem.init(0)
|
|
}
|
|
|
|
// add increments (+ve delta) or decrements (-ve delta) task count by delta
|
|
// and unblocks any wait() calls if task count becomes zero.
|
|
// add panics if task count drops below zero.
|
|
pub fn (mut wg WaitGroup) add(delta int) {
|
|
old_nrjobs := int(C.atomic_fetch_add_u32(&wg.task_count, u32(delta)))
|
|
new_nrjobs := old_nrjobs + delta
|
|
mut num_waiters := C.atomic_load_u32(&wg.wait_count)
|
|
if new_nrjobs < 0 {
|
|
panic('Negative number of jobs in waitgroup')
|
|
}
|
|
|
|
if new_nrjobs == 0 && num_waiters > 0 {
|
|
// clear waiters
|
|
for !C.atomic_compare_exchange_weak_u32(&wg.wait_count, &num_waiters, 0) {
|
|
if num_waiters == 0 {
|
|
return
|
|
}
|
|
}
|
|
for (num_waiters > 0) {
|
|
wg.sem.post()
|
|
num_waiters--
|
|
}
|
|
}
|
|
}
|
|
|
|
// done is a convenience fn for add(-1)
|
|
pub fn (mut wg WaitGroup) done() {
|
|
wg.add(-1)
|
|
}
|
|
|
|
// wait blocks until all tasks are done (task count becomes zero)
|
|
pub fn (mut wg WaitGroup) wait() {
|
|
nrjobs := int(C.atomic_load_u32(&wg.task_count))
|
|
if nrjobs == 0 {
|
|
// no need to wait
|
|
return
|
|
}
|
|
C.atomic_fetch_add_u32(&wg.wait_count, 1)
|
|
wg.sem.wait() // blocks until task_count becomes 0
|
|
}
|