examples: add sync_pool.v for easier testing/diagnosing issues with the sync.pool implementation on different platforms

examples/sync_pool.v

@@ -0,0 +1,44 @@
+// This example illustrates how to use `sync.pool`,
+// and how the various settings for VJOBS, work items etc can interact.
+@[has_globals]
+module main
+
+import log
+import time
+import runtime
+import sync.pool
+
+const args = arguments()
+const nitems = args[1] or { '10' }.int()
+const njobs = args[2] or { runtime.nr_jobs().str() }.int()
+const delay = args[3] or { '1000' }.int()
+
+__global msgs = chan string{cap: 1000}
+
+fn worker_sleep(mut p pool.PoolProcessor, item_idx int, worker_id int) voidptr {
+	item := p.get_item[int](item_idx)
+	msgs <- '# worker_id: ${worker_id:3}, item_idx: ${item_idx + 1:03}, item: ${item:6}, started'
+	time.sleep(delay * time.millisecond)
+	msgs <- '# worker_id: ${worker_id:3}, item_idx: ${item_idx + 1:03}, item: ${item:6}, finished.'
+	return pool.no_result
+}
+
+fn logger() {
+	for {
+		msg := <-msgs
+		log.info(msg)
+		if msg == '>>> done' {
+			break
+		}
+	}
+}
+
+fn main() {
+	t := spawn logger()
+	msgs <- '>>> nitems: ${nitems:6} | njobs: ${njobs:6} | delay_ms: ${delay:6}'
+	items := []int{len: nitems, init: index * 1000}
+	mut fetcher_pool := pool.new_pool_processor(callback: worker_sleep)
+	fetcher_pool.work_on_items(items)
+	msgs <- '>>> done'
+	t.wait()
+}