Add interface for querying numbers of delegated threads.

Author: insertinterestingnamehere

include/qt_threadpool.h

@@ -19,5 +19,6 @@ typedef enum {
 hw_pool_init_status hw_pool_init(uint32_t num_threads);
 void hw_pool_destroy();
 void run_on_current_pool(qt_threadpool_func_type func, void *arg);
+uint32_t get_num_delegated_threads();
 
 #endif

src/threadpool.c

@@ -382,9 +382,11 @@ API_FUNC __attribute__((no_sanitize("memory"))) void hw_pool_destroy() {
   atomic_store_explicit(&hw_pool.num_threads, 0, memory_order_release);
 }
 
-// TODO: interface for querying about the owned thread pool.
-// At least let the user get the number of threads available.
-// If no thread pool is owned, just report a single thread.
+API_FUNC uint32_t get_num_delegated_threads() {
+  if (owned_pool) return owned_pool->num_threads;
+  // Every thread at least has itself available for work.
+  return 1;
+}
 
 // TODO: have the main thread fill the role of thread 0.
 // Instead of having the main thread wait/resume, swap in its thread-locals

test/internal/threadpool.c

@@ -2,13 +2,17 @@
 #include "qt_threadpool.h"
 
 static int on_thread_test(void *arg) {
+  test_check(get_num_delegated_threads() == 1);
   printf("hello from thread\n");
   return 0;
 }
 
 int main() {
+  test_check(get_num_delegated_threads() == 1);
   hw_pool_init(2);
+  test_check(get_num_delegated_threads() == 2);
   hw_pool_destroy();
+  test_check(get_num_delegated_threads() == 1);
   hw_pool_init(2);
   run_on_current_pool(&on_thread_test, NULL);
   hw_pool_destroy();