zos: fix potential event loop stall

trevnorris · liujinye-sys · commit 776a1d070fb8 · 2025-07-21T23:15:42.000+08:00
This is a port of 70002c8 to z/OS to fix the same potential issue that could effectively enter an infinite loop (but not a busy loop) under certain conditions when polling for events. PR-URL: libuv/libuv#2725 Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com> Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com> Reviewed-By: Jameson Nash <vtjnash@gmail.com>
diff --git a/src/unix/os390.c b/src/unix/os390.c
@@ -887,12 +887,13 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
     if (nfds == 0) {
       assert(timeout != -1);
 
-      if (timeout > 0) {
-        timeout = real_timeout - timeout;
-        continue;
-      }
+      if (timeout == 0)
+        return;
 
-      return;
+      /* We may have been inside the system call for longer than |timeout|
+       * milliseconds so we need to update the timestamp to avoid drift.
+       */
+      goto update_timeout;
     }
 
     if (nfds == -1) {
