Commit e5732d2a authored by Ben Gamari's avatar Ben Gamari Committed by Ben Gamari

base: Fix hWaitForInput with timeout on POSIX

This was previously broken (#13252) by
f46369b8, which ported the fdReady
function from `select` to `poll` and in so doing dropping support for
timeouts. Unfortunately, while `select` tells us the amount of time not
slept (on Linux anyways; it turns out this is implementation dependent),
`poll` does not give us this luxury. Consequently, we manually need to
track time slept in this case.

Unfortunately, portably measuring time is hard. Ideally we would use
`clock_gettime` with the monotonic clock here, but sadly this isn't
supported on most versions of Darwin. Consequently, we instead use
`gettimeofday`, running the risk of system time changes messing us up.

Test Plan: Validate

Reviewers: simonmar, austin, hvr

Reviewed By: simonmar

Subscribers: rwbarton, thomie

GHC Trac Issues: #13252

Differential Revision: https://phabricator.haskell.org/D3473
parent 3672cf6d
......@@ -9,11 +9,13 @@
#include "HsBase.h"
#if !defined(_WIN32)
#include <poll.h>
#include <sys/time.h>
#endif
/*
* inputReady(fd) checks to see whether input is available on the file
* descriptor 'fd'. Input meaning 'can I safely read at least a
* descriptor 'fd' within 'msecs' milliseconds (or indefinitely if 'msecs' is
* negative). "Input is available" is defined as 'can I safely read at least a
* *character* from this file object without blocking?'
*/
int
......@@ -21,23 +23,41 @@ fdReady(int fd, int write, int msecs, int isSock)
{
#if !defined(_WIN32)
struct pollfd fds[1];
// We only handle msecs == 0 on non-Windows, because this is the
// only case we need. Non-zero waiting is handled by the IO manager.
if (msecs != 0) {
fprintf(stderr, "fdReady: msecs != 0, this shouldn't happen");
abort();
// if we need to track the then record the current time in case we are
// interrupted.
struct timeval tv0;
if (msecs > 0) {
if (gettimeofday(&tv0, NULL) != 0) {
fprintf(stderr, "fdReady: gettimeofday failed: %s\n",
strerror(errno));
abort();
}
}
struct pollfd fds[1];
fds[0].fd = fd;
fds[0].events = write ? POLLOUT : POLLIN;
fds[0].revents = 0;
int res;
while ((res = poll(fds, 1, 0)) < 0) {
if (errno != EINTR) {
while ((res = poll(fds, 1, msecs)) < 0) {
if (errno == EINTR) {
if (msecs > 0) {
struct timeval tv;
if (gettimeofday(&tv, NULL) != 0) {
fprintf(stderr, "fdReady: gettimeofday failed: %s\n",
strerror(errno));
abort();
}
int elapsed = 1000 * (tv.tv_sec - tv0.tv_sec)
+ (tv.tv_usec - tv0.tv_usec) / 1000;
msecs -= elapsed;
if (msecs <= 0) return 0;
tv0 = tv;
}
} else {
return (-1);
}
}
......
import System.Posix.Files
import System.IO
import System.Timeout
main :: IO ()
main = do
hWaitForInput stdin (5 * 1000)
createNamedPipe "test" accessModes
h <- openFile "test" ReadMode
hWaitForInput h (5 * 1000)
return ()
......@@ -212,4 +212,4 @@ test('T13191',
, only_ways(['normal'])],
compile_and_run,
['-O'])
test('T13525', expect_broken(13525), compile_and_run, [''])
test('T13525', normal, compile_and_run, [''])
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