WIP: readline: ctrl+c close stdin

[mdavidsaver]

My attempt at #670. Provokes readline() and getc() to return immediately, and so also interrupts interactive iocsh(NULL) . Only interrupts iocsh(NULL), just as an exit iocsh command currently does. Depends on IOC skeleton to

Consequential differences with #671.

• Does not call epicsExit().
• Instead of close(0), uses dup2() to atomically replace stdin with /dev/null to avoid potential race with re-use of FD zero.
• Avoids a new worker thread
• Signal handler only installed while waiting for input. Same as libreadline, so no new scope for conflicts.
• Uses sigaction() to also save/restore handler flags.
• Set SA_RESETHAND handler flag so that a repeated signal will trigger the default handler.
• No changes to thread signal masks. (does not matter which thread runs this handler)

Unnecessary differences, which could/should be removed.

• A bunch of calls to fprintf() for troubleshooting, which is not signal-safe.
• Clones, and later replaces, original stdin after interruption. Theoretically allows calling iocsh(NULL) in a loop with multiple interruptions.
  • Second dup2() to restore stdin loses FD flags. (could save/restore flags as well)
• Set SA_RESTART flag to approximate BSD behavior. Maybe reduces testing matrix.
• Does not handle SIGTERM.

[mdavidsaver]

@dirk-zimoch I wrote this code as I do not think I was explaining myself properly in the #671 thread. I am happy to leave this PR as an example.

[AppVeyorBot]

✅ Build EPICS Base 7 base-7.0-1782 completed (commit e976b22926 by @mdavidsaver)

[mdavidsaver]

fyi. testing with modified ralphlange/procServ#70 with --grace-period argument.

./procServ -d -f --killsig 2 --grace-period 3 5678 ~/epics/base-git/bin/linux-x86_64/softIoc
...
epics> var atExitDebug 1

Concurrent killall -TERM procServ triggers:

epics> SigTerm received
Sending signal 2 to pid 802292
Start child cleanup timer 3 sec.
atExit errlogExitHandler(0x55e14e855930)
atExit rlExit((nil))
atExit syncShutdown((nil))
atExit decShutdown((nil))
atExit dbndShutdown((nil))
atExit arrShutdown((nil))
processItem: Got error reading input connection: Input/output error

@@@ @@@ @@@ @@@ @@@
@@@ Received a sigChild for process 802292. Normal exit status = 0
Deleting connection 0x55a192657c90
@@@ Current time: Sun Jul  6 17:02:01 2025
@@@ Child process is shutting down, oneshot mode: server will exit
~connectionItem()
child exits
Close sockets
~clientItem(); handle 0 closed
~connectionItem()
~acceptItem()
~connectionItem()
Cleanup pid and info files

[codacy-production]

Not up to standards ⛔

🔴 Issues 1 high · 2 medium

Alerts:
⚠ 3 issues (≤ 0 issues of at least minor severity)

Results:
3 new issues

Category	Results
UnusedCode	2 medium
Security	1 high

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🟢 Metrics 6 complexity

Metric	Results
Complexity	6

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[mdavidsaver]

Rebased with no changes. My casual testing over the past year has not turned up any misbehavior.

[AppVeyorBot]

✅ Build EPICS Base 7 base-7.0-2379 completed (commit c3f7922ffa by @mdavidsaver)