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Improve cancellations, randomness, and time

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- Exhaustively document cancellation points
- Rename SIGCANCEL to SIGTHR just like BSDs
- Further improve POSIX thread cancellations
- Ensure asynchronous cancellations work correctly
- Elevate the quality of getrandom() and getentropy()
- Make futexes cancel correctly on OpenBSD 6.x and 7.x
- Add reboot.com and shutdown.com to examples directory
- Remove underscore prefix from awesome timespec_*() APIs
- Create assertions that help verify our cancellation points
- Remove bad timespec APIs (cmp generalizes eq/ne/gt/gte/lt/lte)
This commit is contained in:
Justine Tunney 2022-11-05 19:49:41 -07:00
parent 0d7c265392
commit 3f0bcdc3ef
No known key found for this signature in database
GPG key ID: BE714B4575D6E328
173 changed files with 1599 additions and 782 deletions
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69
third_party/nsync/futex.c vendored
View file

@ -28,6 +28,7 @@
#include "libc/errno.h"
#include "libc/intrin/atomic.h"
#include "libc/intrin/describeflags.internal.h"
#include "libc/intrin/kprintf.h"
#include "libc/intrin/strace.internal.h"
#include "libc/intrin/weaken.h"
#include "libc/limits.h"
@ -38,6 +39,7 @@
#include "libc/sysv/consts/timer.h"
#include "libc/sysv/errfuns.h"
#include "libc/thread/freebsd.internal.h"
#include "libc/thread/posixthread.internal.h"
#include "libc/thread/thread.h"
#include "libc/thread/tls.h"
#include "third_party/nsync/atomic.h"
@ -118,26 +120,26 @@ static int nsync_futex_polyfill_ (atomic_int *w, int expect, struct timespec *ti
int64_t nanos, maxnanos;
struct timespec ts, deadline;
ts = nsync_time_now ();
ts = timespec_real ();
if (!timeout) {
deadline = nsync_time_no_deadline;
deadline = timespec_max;
} else if (FUTEX_TIMEOUT_IS_ABSOLUTE) {
deadline = *timeout;
} else {
deadline = nsync_time_add (ts, *timeout);
deadline = timespec_add (ts, *timeout);
}
nanos = 100;
maxnanos = __SIG_POLLING_INTERVAL_MS * 1000L * 1000;
while (nsync_time_cmp (deadline, ts) > 0) {
ts = nsync_time_add (ts, _timespec_fromnanos (nanos));
if (nsync_time_cmp (ts, deadline) > 0) {
while (timespec_cmp (deadline, ts) > 0) {
ts = timespec_add (ts, timespec_fromnanos (nanos));
if (timespec_cmp (ts, deadline) > 0) {
ts = deadline;
}
if (atomic_load_explicit (w, memory_order_acquire) != expect) {
return 0;
}
if ((rc = nsync_time_sleep_until (ts))) {
if ((rc = timespec_sleep_until (ts))) {
return -rc;
}
if (nanos < maxnanos) {
@ -159,22 +161,22 @@ static int nsync_futex_wait_win32_ (atomic_int *w, int expect, char pshare, stru
if (timeout) {
deadline = *timeout;
} else {
deadline = nsync_time_no_deadline;
deadline = timespec_max;
}
while (!(rc = _check_interrupts (false, 0))) {
now = nsync_time_now ();
if (nsync_time_cmp (now, deadline) > 0) {
now = timespec_real ();
if (timespec_cmp (now, deadline) > 0) {
rc = etimedout();
break;
}
remain = nsync_time_sub (deadline, now);
interval = _timespec_frommillis (__SIG_POLLING_INTERVAL_MS);
wait = nsync_time_cmp (remain, interval) > 0 ? interval : remain;
remain = timespec_sub (deadline, now);
interval = timespec_frommillis (__SIG_POLLING_INTERVAL_MS);
wait = timespec_cmp (remain, interval) > 0 ? interval : remain;
if (atomic_load_explicit (w, memory_order_acquire) != expect) {
break;
}
if (WaitOnAddress (w, &expect, sizeof(int), _timespec_tomillis (wait))) {
if (WaitOnAddress (w, &expect, sizeof(int), timespec_tomillis (wait))) {
break;
} else {
ASSERT (GetLastError () == ETIMEDOUT);
@ -186,6 +188,7 @@ static int nsync_futex_wait_win32_ (atomic_int *w, int expect, char pshare, stru
int nsync_futex_wait_ (atomic_int *w, int expect, char pshare, struct timespec *timeout) {
int e, rc, op, fop;
struct PosixThread *pt = 0;
if (atomic_load_explicit (w, memory_order_acquire) != expect) {
return -EAGAIN;
@ -210,21 +213,31 @@ int nsync_futex_wait_ (atomic_int *w, int expect, char pshare, struct timespec *
} else if (IsFreebsd ()) {
rc = sys_umtx_timedwait_uint (w, expect, pshare, timeout);
} else {
rc = sys_futex_cp (w, op, expect, timeout, 0, FUTEX_WAIT_BITS_);
if (IsOpenbsd() && rc > 0) {
// OpenBSD futex() returns errors as
// positive numbers without setting the
// carry flag. It's an irregular miracle
// because OpenBSD returns ECANCELED if
// futex() is interrupted w/ SA_RESTART
// so we're able to tell it apart from
// PT_MASKED which causes the wrapper
// to put ECANCELED into errno.
if (rc == ECANCELED) {
rc = EINTR;
if (IsOpenbsd()) {
// OpenBSD 6.8 futex() returns errors as
// positive numbers, without setting CF.
// This irregularity is fixed in 7.2 but
// unfortunately OpenBSD futex() defines
// its own ECANCELED condition, and that
// overlaps with our system call wrapper
if ((pt = (struct PosixThread *)__get_tls()->tib_pthread)) {
pt->flags &= ~PT_OPENBSD_KLUDGE;
}
}
rc = sys_futex_cp (w, op, expect, timeout, 0, FUTEX_WAIT_BITS_);
if (IsOpenbsd()) {
// Handle the OpenBSD 6.x irregularity.
if (rc > 0) {
errno = rc;
rc = -1;
}
// Check if ECANCELED came from the kernel
// because a SA_RESTART signal handler was
// invoked, such as our SIGTHR callback.
if (rc == -1 && errno == ECANCELED &&
pt && (~pt->flags & PT_OPENBSD_KLUDGE)) {
errno = EINTR;
}
errno = rc;
rc = -1;
}
}
if (rc == -1) {