| Ticket UUID: | 7aa8fd34c4e8ed00e73e06aef189fae1b092d1c4 | ||
| Title: | epoll notifier spins and never reports writable after EPOLLERR | ||
| Type: | Bug | Created on: | 2026-10-16 21:46:10 |
| Submitter: | serhiy.storchaka | Assigned to: | jan.nijtmans |
| Subsystem: | 01. Notifier | Severity: | Minor |
| Priority: | 5 Medium | Last modified: | 2026-10-30 09:40:46 |
| Status: | Closed | Closed by: | jan.nijtmans |
| Resolution: | Fixed | Closed on: | 2026-10-30 09:40:46 |
| Version: | 9.0.5, 9.1.0 | ||
| Description: | ||||
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On Linux (epoll notifier, 8.7 and later), a writable handler on a pipe whose reader has exited never fires: EPOLLERR is translated only to TCL_EXCEPTION, and the level-triggered event wakes epoll_wait() again at once, so the process spins at 100% CPU. A background flush to such a pipe never ends, and [close] reports no error although the data was lost.
set f [open |[list [info nameofexecutable] exit.tcl] w] ;# child exits at once
fconfigure $f -blocking 0
puts -nonewline $f [string repeat x 300000]
catch {flush $f}
chan event $f writable {set w writable}
after 3000 {set w timeout}
vwait w ;# 8.6: writable at once, close gives "broken pipe"; 9.x: timeout, close gives no error
select() reports such a descriptor as writable. The code is from [858569fb04]. | ||||
| User Comments: | ||||
serhiy.storchaka added on 2026-10-16 21:49:57:
Proposed fix in branch epoll-error-writable: report EPOLLERR as readable and writable, like select() does. Test io-78.1. jan.nijtmans added on 2026-10-30 09:40:46:
Fixed in [6d788a0eb3|trunk], and core-9-0-branch Many thanks! | ||||