xwin-xdg-menu high cpu usage with rxvt-unicode

[Takashi Yano]

On Mon, 21 Jun 2021 05:49:28 +0000
Viet-Duc Le wrote:
> Hi,
> 
> I've encountered a peculiar issue with rxvt-unicode launched from xwin-xdg-menu (20170321-1)
> The image below corresponds to two rxvt-unicode instances, each occupies 30% of system resouce.
> https://imgur.com/a/FTFwIrZ
> I'm using the the latest version of cygwin. 'cygcheck.out' is attached per guideline.
> 
> Steps to reproduce:
> - Start XWin Server from Start menu
> - X applications menu -> System Tools -> rxvt-unicode
> - Kill rxvt-unicode to free the resource again
> 
> Other observations:
> - XTerm does not incur high resources.
> - Manually launching rxvt-unicode from XTerm does not incur high resources.
> 
> I think this is not an issue with rxvt but with xwin-xdg-menu.
> On laptop, it is very noticeable when the fan kicks in.
> Insights and suggestions are much appreciated.
> 
> Thanks.
> Viet-Duc

I looked into this problem and found the cause.
urxvt seems to close stdout while xwin-xdg-menu use select()
to read stdout of the launched apps. Since stdout is closed,
select() returns repeatedly without any output. This causes
high cpu load.

I also confirmed that the following patch for xwin-xdg-menu
resolves the issue.

--- execute.c.orig	2017-03-22 05:31:53.000000000 +0900
+++ execute.c	2021-06-22 10:47:28.917675400 +0900
@@ -100,30 +100,38 @@
 
     default: /* parent */
     {
+        int stdout_ok = TRUE, stderr_ok = TRUE;
         close(stdout_filedes[1]);
         close(stderr_filedes[1]);
 
         printf("executing '%s', pid %d\n", (char *) cmd, pid);
 
         /* read from pipes, write to log, until both are closed */
-        while (TRUE) {
+        while (stdout_ok || stderr_ok) {
             fd_set readfds, errorfds;
-            int nfds = max(stdout_filedes[0], stderr_filedes[0]) + 1;
+            int nfds = 0;
 
             FD_ZERO(&readfds);
-            FD_SET(stdout_filedes[0], &readfds);
-            FD_SET(stderr_filedes[0], &readfds);
+            if (stdout_ok) {
+                FD_SET(stdout_filedes[0], &readfds);
+                nfds = max(nfds, stdout_filedes[0] + 1);
+            }
+            if (stderr_ok) {
+                FD_SET(stderr_filedes[0], &readfds);
+                nfds = max(nfds, stderr_filedes[0] + 1);
+            }
             errorfds = readfds;
 
             if (select(nfds, &readfds, NULL, &errorfds, NULL) > 0) {
-                if (FD_ISSET(stdout_filedes[0], &readfds))
+                if (FD_ISSET(stdout_filedes[0], &errorfds))
+                    stdout_ok = FALSE;
+                else if (FD_ISSET(stdout_filedes[0], &readfds))
                     LogLineFromFd(stdout_filedes[0], "stdout", pid);
-                if (FD_ISSET(stderr_filedes[0], &readfds))
-                    LogLineFromFd(stderr_filedes[0], "stderr", pid);
 
-                if (FD_ISSET(stdout_filedes[0], &errorfds) &&
-                    FD_ISSET(stderr_filedes[0], &errorfds))
-                    break;
+                if (FD_ISSET(stderr_filedes[0], &errorfds))
+                    stderr_ok = FALSE;
+                else if (FD_ISSET(stderr_filedes[0], &readfds))
+                    LogLineFromFd(stderr_filedes[0], "stderr", pid);
             }
             else {
                 break;


Jon, could you please have a look?

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>