sync,strings,cgen: reduce memory consumption in cgen

vlib/sync/pool/pool.v

@@ -81,12 +81,10 @@ pub fn (mut pool PoolProcessor) work_on_pointers(items []voidptr) {
 	if pool.njobs > 0 {
 		njobs = pool.njobs
 	}
-	pool.items = []
-	pool.results = []
-	pool.thread_contexts = []
+	pool.thread_contexts = []voidptr{len: items.len}
+	pool.results = []voidptr{len: items.len}
+	pool.items = []voidptr{cap: items.len}
 	pool.items << items
-	pool.results = []voidptr{len: (pool.items.len)}
-	pool.thread_contexts << []voidptr{len: (pool.items.len)}
 	pool.waitgroup.add(njobs)
 	for i := 0; i < njobs; i++ {
 		if njobs > 1 {
@@ -129,13 +127,22 @@ pub fn (pool &PoolProcessor) get_result<T>(idx int) T {
 
 // get_results - get a list of type safe results in the main thread.
 pub fn (pool &PoolProcessor) get_results<T>() []T {
-	mut res := []T{}
+	mut res := []T{cap: pool.results.len}
 	for i in 0 .. pool.results.len {
 		res << *(&T(pool.results[i]))
 	}
 	return res
 }
 
+// get_results_ref - get a list of type safe results in the main thread.
+pub fn (pool &PoolProcessor) get_results_ref<T>() []&T {
+	mut res := []&T{cap: pool.results.len}
+	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.

vlib/sync/pool/pool_test.v

@@ -34,6 +34,11 @@ fn test_work_on_strings() {
 		println(x.s)
 		assert x.s.len > 1
 	}
+	println('---------- pool_s.get_results_ref: --------------')
+	for x in pool_s.get_results_ref<SResult>() {
+		println(x.s)
+		assert x.s.len > 1
+	}
 }
 
 fn test_work_on_ints() {
@@ -49,4 +54,9 @@ fn test_work_on_ints() {
 		println(x.i)
 		assert x.i > 100
 	}
+	println('---------- pool_i.get_results_ref: --------------')
+	for x in pool_i.get_results_ref<IResult>() {
+		println(x.i)
+		assert x.i > 100
+	}
 }