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bug#1082: 23.0.60; read-char unexpectedly halts execution of script
From: |
Chong Yidong |
Subject: |
bug#1082: 23.0.60; read-char unexpectedly halts execution of script |
Date: |
Mon, 06 Oct 2008 15:35:28 -0400 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux) |
Chong Yidong <cyd@stupidchicken.com> writes:
>> Let filter.el consist of the forms:
>>
>> (defun bc-filter (proc string)
>> (message "%s" string))
>>
>> (message "starting")
>> (setq bc (start-process "bc" nil "/usr/bin/bc"))
>> (set-process-filter bc 'bc-filter)
>>
>> (while t
>> (let ((char (read-char nil nil 0.1)))
>> (message "char: %s" char)))
>>
>> Where "/usr/bin/bc" is the GNU arbitrary precision calculator. Now:
>>
>> mt-computer:~ mt$ emacs --script filter.el
>> starting
>> mt-computer:~ mt$
>>
>> I expect non-termination in this case
>
> This broke when SYNC_INPUT became the default.
To pin it down further, this breakage seems to be due to not using
SA_RESTART in the signal handler. If we set SA_RESTARTi in sysdep.c,
the problem disappears. Stefan, could you comment?
signal_handler_t
sys_signal (int signal_number, signal_handler_t action)
{
struct sigaction new_action, old_action;
sigemptyset (&new_action.sa_mask);
new_action.sa_handler = action;
#if defined (SA_RESTART) && ! defined (BROKEN_SA_RESTART) &&
!defined(SYNC_INPUT)
/* Emacs mostly works better with restartable system services. If this
flag exists, we probably want to turn it on here.
However, on some systems this resets the timeout of `select'
which means that `select' never finishes if it keeps getting signals.
BROKEN_SA_RESTART is defined on those systems. */
/* It's not clear why the comment above says "mostly works better". --Stef
When SYNC_INPUT is set, we don't want SA_RESTART because we need to poll
for pending input so we need long-running syscalls to be interrupted
after a signal that sets the interrupt_input_pending flag. */
new_action.sa_flags = SA_RESTART;
#else
new_action.sa_flags = 0;
#endif
sigaction (signal_number, &new_action, &old_action);
return (old_action.sa_handler);
}