Thread pools: create threads in detached state.

This prevents theoretical resource leak, since those threads are never joined.

Found with ThreadSanitizer.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

src/core/ngx_thread_pool.c

diff --git a/src/core/ngx_thread_pool.c b/src/core/ngx_thread_pool.c
index f3655aa..7fb0f7f 100644
--- a/src/core/ngx_thread_pool.c
+++ b/src/core/ngx_thread_pool.c
@@ -137,6 +137,13 @@
         return NGX_ERROR;
     }
 
+    err = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
+    if (err) {
+        ngx_log_error(NGX_LOG_ALERT, log, err,
+                      "pthread_attr_setdetachstate() failed");
+        return NGX_ERROR;
+    }
+
 #if 0
     err = pthread_attr_setstacksize(&attr, PTHREAD_STACK_MIN);
     if (err) {