## retry-syscall-in-eintr.pkg
#
# Some system calls may take a long time
# to complete and may be interrupted by
# timer signals before they complete.
#
# This module implements a simple hack to
# partially protect against this problem.
#
# For a longer discussion see comments at bottom of:
#
# src/c/lib/socket/connect.c
#
# This hack gets used in:
# src/lib/x-kit/xclient/pkg/wire/display.pkg# Compiled by:
# src/lib/std/standard.libstipulate
package log = logger; # logger is from src/lib/src/lib/thread-kit/src/lib/logger.pkg package ts = thread_scheduler; # thread_scheduler is from src/lib/src/lib/thread-kit/src/core-thread-kit/thread-scheduler.pkg package psx = posix_1003_1b; # posix_1003_1b is from src/lib/std/src/posix-1003.1b/posix-1003-1b.pkgherein
package retry_syscall_on_eintr: (weak) api {
is_intr: winix::System_Error -> Bool;
#
# Return TRUE iff error was due to system
# call being interrupted -- that is, if it
# returned posix EINTR in errno.
do_syscall_retry_on_eintr: (X -> Y) -> X -> Y;
#
# Do a system call, and restart if it is interrupted
# (that is, if it returns posix EINTR in errno).
do_atomic_syscall: (X -> Y) -> X -> Y;
#
# Do a system call with timer signals masked (i.e., SIGALRM ignored)
tracing: file::Logtree_Node; # Controls printing of thread watching messages.
} {
tracing = log::make_logtree_leaf { parent => file::all_logging, name => "retry_syscall_tracing" };
to_log = log::log_if tracing; # Conditionally write strings to tracing.log or whatever.
#
# To debug via tracelogging, annotate the code with lines like
#
# to_log .{ sprintf "foo/top: bar d=%d" bar; };
fun is_intr err
=
err == psx::error::intr; # == posix EINTR.
fun do_atomic_syscall f x
=
{
# Note that stopping the timer will stop all
# thread_scheduler timeslicing dead in its
# tracks, including all threads attempting to
# maintain periodic user interface stuff etc.
#
# This is probably a REALLY BAD IDEA. XXX BUGGO FIXME
#
ts::stop_thread_scheduler_timer();
#
# XXX BUGGO FIXME this is still pretty slapdash;
# we can still get interrupted by
# signals like SIGCHLD, and if we
# do we're screwed.
result = (f x)
except
x = {
ts::restart_thread_scheduler_timer ();
raise exception x;
};
ts::restart_thread_scheduler_timer ();
result;
};
# This function is only called in
#
# src/lib/std/src/posix/threadkit-winix-data-file-io-driver-for-posix.pkg #
# where it protects a few read() and write() calls;
# if any other "slow" system call is interrupted,
# we are still screwed. :-( XXX BUGGO FIXME
#
fun do_syscall_retry_on_eintr f x
=
try 3
where
fun try 0
=>
do_atomic_syscall f x;
try n
=>
(f x)
except
(ex as winix::RUNTIME_EXCEPTION(_, THE err))
=
if (is_intr err) try (n - 1);
else raise exception ex;
fi;
end;
end;
};
end;
## COPYRIGHT (c) 1996 AT&T Research.
## Subsequent changes by Jeff Prothero Copyright (c) 2010-2012,
## released under Gnu Public Licence version 3.