v/vlib/sync/pool.v

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module sync
// * Goal: this file provides a convenient way to run identical tasks over a list
// * of items in parallel, without worrying about waitgroups, mutexes and so on.
// *
// * Usage example:
// * struct SResult{ s string }
// * fn sprocess(p &sync.PoolProcessor, idx, wid int) voidptr {
// * item := p.get_item<string>(idx)
// * println('idx: $idx, wid: $wid, item: ' + item)
// * return &SResult{ item.reverse() }
// * }
// * pool := sync.new_pool_processor({ callback: sprocess })
// * pool.work_on_items(['a','b','c','d','e','f','g'])
// * // optionally, you can iterate over the results too:
// * for x in pool.get_results<SResult>() {
// * println('result: $x.s')
// * }
// *
// * See https://github.com/vlang/v/blob/master/vlib/sync/pool_test.v for a
// * more detailed usage example.
// *
// * After all the work is done in parallel by the worker threads in the pool,
// * pool.work_on_items will return, and you can then call
// * pool.get_results<Result>() to retrieve a list of all the results,
// * that the worker callbacks returned for each item that you passed.
// * The parameters of new_pool_processor are:
// * context.maxjobs: when 0 (the default), the PoolProcessor will use an
// * optimal for your system number of threads to process your items
// * context.callback: this should be a callback function, that each worker
// * thread in the pool will run for each item.
// * The callback function will receive as parameters:
// * 1) the PoolProcessor instance, so it can call
// * p.get_item<int>(idx) to get the actual item at index idx
// * NB: for now, you are better off calling p.get_string_item(idx)
// * or p.get_int_item(idx) ; TODO: vfmt and generics
// * 2) idx - the index of the currently processed item
// * 3) task_id - the index of the worker thread in which the callback
// * function is running.
import runtime
pub const (
no_result = voidptr(0)
)
pub struct PoolProcessor {
thread_cb voidptr
mut:
njobs int
items []voidptr
results []voidptr
ntask int // writing to this should be locked by ntask_mtx.
ntask_mtx &sync.Mutex
waitgroup &sync.WaitGroup
shared_context voidptr
thread_contexts []voidptr
}
pub type ThreadCB fn(p &PoolProcessor, idx int, task_id int)voidptr
pub struct PoolProcessorConfig {
maxjobs int
callback ThreadCB
}
// new_pool_processor returns a new PoolProcessor instance.
pub fn new_pool_processor(context PoolProcessorConfig) &PoolProcessor {
if isnil(context.callback) {
panic('You need to pass a valid callback to new_pool_processor.')
}
// TODO: remove this call.
// It prevents a V warning about unused module runtime.
runtime.nr_jobs()
pool := &PoolProcessor {
items: []
results: []
shared_context: voidptr(0)
thread_contexts: []
njobs: context.maxjobs
ntask: 0
ntask_mtx: sync.new_mutex()
waitgroup: sync.new_waitgroup()
thread_cb: context.callback
}
return pool
}
// set_max_jobs gives you the ability to override the number
// of jobs *after* the PoolProcessor had been created already.
pub fn (pool mut PoolProcessor) set_max_jobs(njobs int) {
pool.njobs = njobs
}
// work_on_items receives a list of items of type T,
// then starts a work pool of pool.njobs threads, each running
// pool.thread_cb in a loop, untill all items in the list,
// are processed.
// When pool.njobs is 0, the number of jobs is determined
// by the number of available cores on the system.
// work_on_items returns *after* all threads finish.
// You can optionally call get_results after that.
pub fn (pool mut PoolProcessor) work_on_items<T>(items []T) {
pool.work_on_pointers( items.pointers() )
}
pub fn (pool mut PoolProcessor) work_on_pointers(items []voidptr) {
mut njobs := runtime.nr_jobs()
if pool.njobs > 0 {
njobs = pool.njobs
}
pool.items = []
pool.results = []
pool.thread_contexts = []
pool.items << items
pool.results = [voidptr(0)].repeat(pool.items.len)
pool.thread_contexts << [voidptr(0)].repeat(pool.items.len)
pool.waitgroup.add(njobs)
for i := 0; i < njobs; i++ {
go process_in_thread(pool,i)
}
pool.waitgroup.wait()
}
// process_in_thread does the actual work of worker thread.
// It is a workaround for the current inability to pass a
// method in a callback.
fn process_in_thread(pool mut PoolProcessor, task_id int) {
cb := ThreadCB(pool.thread_cb)
mut idx := 0
ilen := pool.items.len
for {
if pool.ntask >= ilen {
break
}
pool.ntask_mtx.lock()
idx = pool.ntask
pool.ntask++
pool.ntask_mtx.unlock()
if idx >= ilen {
break
}
pool.results[idx] = cb(pool, idx, task_id)
}
pool.waitgroup.done()
}
// get_item - called by the worker callback.
// Retrieves a type safe instance of the currently processed item
pub fn (pool &PoolProcessor) get_item<T>(idx int) T {
return *(&T(pool.items[idx]))
}
// get_string_item - called by the worker callback.
// It does not use generics so it does not mess up vfmt.
// TODO: remove the need for this when vfmt becomes smarter.
pub fn (pool &PoolProcessor) get_string_item(idx int) string {
return *(&string(pool.items[idx]))
}
// get_int_item - called by the worker callback.
// It does not use generics so it does not mess up vfmt.
// TODO: remove the need for this when vfmt becomes smarter.
pub fn (pool &PoolProcessor) get_int_item(idx int) int {
return *(&int(pool.items[idx]))
}
pub fn (pool &PoolProcessor) get_result<T>(idx int) T {
return *(&T(pool.results[idx]))
}
// get_results - can be called to get a list of type safe results.
pub fn (pool &PoolProcessor) get_results<T>() []T {
mut res := []T
for i in 0 .. pool.results.len {
res << *(&T(pool.results[i]))
}
return res
}
// set_shared_context - can be called during the setup so that you can
// provide a context that is shared between all worker threads, like
// common options/settings.
pub fn (pool mut PoolProcessor) set_shared_context(context voidptr) {
pool.shared_context = context
}
// get_shared_context - can be called in each worker callback, to get
// the context set by pool.set_shared_context
pub fn (pool &PoolProcessor) get_shared_context() voidptr {
return pool.shared_context
}
// set_thread_context - can be called during the setup at the start of
// each worker callback, so that the worker callback can have some thread
// local storage area where it can write/read information that is private
// to the given thread, without worrying that it will get overwritten by
// another thread
pub fn (pool mut PoolProcessor) set_thread_context(idx int, context voidptr) {
pool.thread_contexts[idx] = context
}
// get_thread_context - returns a pointer, that was set with
// pool.set_thread_context . This pointer is private to each thread.
pub fn (pool &PoolProcessor) get_thread_context(idx int) voidptr {
return pool.thread_contexts[idx]
}