| Ticket UUID: | 21dbc600ae0a005a7f879a05580550a8da257b14 | ||
| Title: | exec hangs, iff stdin & stdout both were previously closed. | ||
| Type: | Bug | Created on: | 2022-12-06 11:45:49 |
| Submitter: | avl42 | Assigned to: | nobody |
| Subsystem: | 16. Commands A-H | Severity: | Severe |
| Priority: | 5 Medium | Last modified: | 2026-10-20 21:28:10 |
| Status: | Open | Closed by: | nobody |
| Resolution: | None | Closed on: | |
| Version: | 8.6.18, 9.0.5, 9.1.0 | ||
| Description: | ||||
simplest test script: close stdin; close stdout; exec true Workaround (assuming that original stdin & -out just need to be closed): close stdin; close stdout; open /dev/null r; exec true In either case: exec first creates a pipe, and while the child runs, the parent waits on that pipe for EOF (probably to be initiated from another thread). With at least one of stdin or stdout NOT closed (or re-opened afterwards), the EOF on that pipe is seen, but with BOTH stdin/-out closed, nothing ever closes the write-end of the pipe. PS: that pipe is NOT the one by which the main process communicates to the child. | ||||
| User Comments: | ||||
serhiy.storchaka added on 2026-10-13 18:34:38:
Still hangs with 8.6.17, 9.0 and 9.1. With stdin and stdout closed, the pipe
for the output of the child gets descriptors 0 and 1, and
Proposed fix in branch exec-closed-stdio: move pipes and files created for a pipeline above descriptor 2. Test exec-23.1. jan.nijtmans added on 2026-10-20 20:53:48:
I'm seeing this compiler warning, even though it appears to work fine:
unix/tclUnixPipe.c:469:13: warning: variable ‘errPipeIn’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Wclobbered]
469 | TclFile errPipeIn, errPipeOut;
| ^~~~~~~~~
unix/tclUnixPipe.c:469:24: warning: variable ‘errPipeOut’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Wclobbered]
469 | TclFile errPipeIn, errPipeOut;
| ^~~~~~~~~~
jan.nijtmans added on 2026-10-20 21:03:20:
This warning is caused by the line pid = fork(); in line 602 serhiy.storchaka added on 2026-10-20 21:28:10:
The warning is not new in this branch: TclpCreateProcess() is unchanged, but unix/tclUnixPipe.c has Fixed in [4af19e7744] on the branch: they are volatile now (TclpCreatePipe() fills plain temporaries). My gcc 15 never showed the warning, so please check that it is gone with yours. | ||||