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openssl/ssl/quic/quic_reactor.c

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/*
* Copyright 2022-2025 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include "internal/quic_reactor.h"
#include "internal/common.h"
#include "internal/thread_arch.h"
#include <assert.h>
/*
* Core I/O Reactor Framework
* ==========================
*/
static void rtor_notify_other_threads(QUIC_REACTOR *rtor);
int ossl_quic_reactor_init(QUIC_REACTOR *rtor,
void (*tick_cb)(QUIC_TICK_RESULT *res, void *arg,
uint32_t flags),
void *tick_cb_arg,
CRYPTO_MUTEX *mutex,
OSSL_TIME initial_tick_deadline,
uint64_t flags)
{
rtor->poll_r.type = BIO_POLL_DESCRIPTOR_TYPE_NONE;
rtor->poll_w.type = BIO_POLL_DESCRIPTOR_TYPE_NONE;
rtor->net_read_desired = 0;
rtor->net_write_desired = 0;
rtor->can_poll_r = 0;
rtor->can_poll_w = 0;
rtor->tick_deadline = initial_tick_deadline;
rtor->tick_cb = tick_cb;
rtor->tick_cb_arg = tick_cb_arg;
rtor->mutex = mutex;
rtor->cur_blocking_waiters = 0;
if ((flags & QUIC_REACTOR_FLAG_USE_NOTIFIER) != 0) {
if (!ossl_rio_notifier_init(&rtor->notifier))
return 0;
if ((rtor->notifier_cv = ossl_crypto_condvar_new()) == NULL) {
ossl_rio_notifier_cleanup(&rtor->notifier);
return 0;
}
rtor->have_notifier = 1;
} else {
rtor->have_notifier = 0;
}
return 1;
}
void ossl_quic_reactor_cleanup(QUIC_REACTOR *rtor)
{
if (rtor == NULL)
return;
if (rtor->have_notifier) {
ossl_rio_notifier_cleanup(&rtor->notifier);
rtor->have_notifier = 0;
ossl_crypto_condvar_free(&rtor->notifier_cv);
}
}
void ossl_quic_reactor_set_poll_r(QUIC_REACTOR *rtor, const BIO_POLL_DESCRIPTOR *r)
{
if (r == NULL)
rtor->poll_r.type = BIO_POLL_DESCRIPTOR_TYPE_NONE;
else
rtor->poll_r = *r;
rtor->can_poll_r
= ossl_quic_reactor_can_support_poll_descriptor(rtor, &rtor->poll_r);
}
void ossl_quic_reactor_set_poll_w(QUIC_REACTOR *rtor, const BIO_POLL_DESCRIPTOR *w)
{
if (w == NULL)
rtor->poll_w.type = BIO_POLL_DESCRIPTOR_TYPE_NONE;
else
rtor->poll_w = *w;
rtor->can_poll_w
= ossl_quic_reactor_can_support_poll_descriptor(rtor, &rtor->poll_w);
}
const BIO_POLL_DESCRIPTOR *ossl_quic_reactor_get_poll_r(const QUIC_REACTOR *rtor)
{
return &rtor->poll_r;
}
const BIO_POLL_DESCRIPTOR *ossl_quic_reactor_get_poll_w(const QUIC_REACTOR *rtor)
{
return &rtor->poll_w;
}
int ossl_quic_reactor_can_support_poll_descriptor(const QUIC_REACTOR *rtor,
const BIO_POLL_DESCRIPTOR *d)
{
return d->type == BIO_POLL_DESCRIPTOR_TYPE_SOCK_FD;
}
int ossl_quic_reactor_can_poll_r(const QUIC_REACTOR *rtor)
{
return rtor->can_poll_r;
}
int ossl_quic_reactor_can_poll_w(const QUIC_REACTOR *rtor)
{
return rtor->can_poll_w;
}
int ossl_quic_reactor_net_read_desired(QUIC_REACTOR *rtor)
{
return rtor->net_read_desired;
}
int ossl_quic_reactor_net_write_desired(QUIC_REACTOR *rtor)
{
return rtor->net_write_desired;
}
OSSL_TIME ossl_quic_reactor_get_tick_deadline(QUIC_REACTOR *rtor)
{
return rtor->tick_deadline;
}
int ossl_quic_reactor_tick(QUIC_REACTOR *rtor, uint32_t flags)
{
QUIC_TICK_RESULT res = {0};
/*
* Note that the tick callback cannot fail; this is intentional. Arguably it
* does not make that much sense for ticking to 'fail' (in the sense of an
* explicit error indicated to the user) because ticking is by its nature
* best effort. If something fatal happens with a connection we can report
* it on the next actual application I/O call.
*/
rtor->tick_cb(&res, rtor->tick_cb_arg, flags);
rtor->net_read_desired = res.net_read_desired;
rtor->net_write_desired = res.net_write_desired;
rtor->tick_deadline = res.tick_deadline;
if (res.notify_other_threads)
rtor_notify_other_threads(rtor);
return 1;
}
RIO_NOTIFIER *ossl_quic_reactor_get0_notifier(QUIC_REACTOR *rtor)
{
return rtor->have_notifier ? &rtor->notifier : NULL;
}
/*
* Blocking I/O Adaptation Layer
* =============================
*/
/*
* Utility which can be used to poll on up to two FDs. This is designed to
* support use of split FDs (e.g. with SSL_set_rfd and SSL_set_wfd where
* different FDs are used for read and write).
*
* Generally use of poll(2) is preferred where available. Windows, however,
* hasn't traditionally offered poll(2), only select(2). WSAPoll() was
* introduced in Vista but has seemingly been buggy until relatively recent
* versions of Windows 10. Moreover we support XP so this is not a suitable
* target anyway. However, the traditional issues with select(2) turn out not to
* be an issue on Windows; whereas traditional *NIX select(2) uses a bitmap of
* FDs (and thus is limited in the magnitude of the FDs expressible), Windows
* select(2) is very different. In Windows, socket handles are not allocated
* contiguously from zero and thus this bitmap approach was infeasible. Thus in
* adapting the Berkeley sockets API to Windows a different approach was taken
* whereby the fd_set contains a fixed length array of socket handles and an
* integer indicating how many entries are valid; thus Windows select()
* ironically is actually much more like *NIX poll(2) than *NIX select(2). In
* any case, this means that the relevant limit for Windows select() is the
* number of FDs being polled, not the magnitude of those FDs. Since we only
* poll for two FDs here, this limit does not concern us.
*
* Usage: rfd and wfd may be the same or different. Either or both may also be
* -1. If rfd_want_read is 1, rfd is polled for readability, and if
* wfd_want_write is 1, wfd is polled for writability. Note that since any
* passed FD is always polled for error conditions, setting rfd_want_read=0 and
* wfd_want_write=0 is not the same as passing -1 for both FDs.
*
* deadline is a timestamp to return at. If it is ossl_time_infinite(), the call
* never times out.
*
* Returns 0 on error and 1 on success. Timeout expiry is considered a success
* condition. We don't elaborate our return values here because the way we are
* actually using this doesn't currently care.
*
* If mutex is non-NULL, it is assumed to be held for write and is unlocked for
* the duration of the call.
*
* Precondition: mutex is NULL or is held for write (unchecked)
* Postcondition: mutex is NULL or is held for write (unless
* CRYPTO_THREAD_write_lock fails)
*/
static int poll_two_fds(int rfd, int rfd_want_read,
int wfd, int wfd_want_write,
int notify_rfd,
OSSL_TIME deadline,
CRYPTO_MUTEX *mutex)
{
#if defined(OPENSSL_SYS_WINDOWS) || !defined(POLLIN)
fd_set rfd_set, wfd_set, efd_set;
OSSL_TIME now, timeout;
struct timeval tv, *ptv;
int maxfd, pres;
# ifndef OPENSSL_SYS_WINDOWS
/*
* On Windows there is no relevant limit to the magnitude of a fd value (see
* above). On *NIX the fd_set uses a bitmap and we must check the limit.
*/
if (rfd >= FD_SETSIZE || wfd >= FD_SETSIZE)
return 0;
# endif
FD_ZERO(&rfd_set);
FD_ZERO(&wfd_set);
FD_ZERO(&efd_set);
if (rfd != INVALID_SOCKET && rfd_want_read)
openssl_fdset(rfd, &rfd_set);
if (wfd != INVALID_SOCKET && wfd_want_write)
openssl_fdset(wfd, &wfd_set);
/* Always check for error conditions. */
if (rfd != INVALID_SOCKET)
openssl_fdset(rfd, &efd_set);
if (wfd != INVALID_SOCKET)
openssl_fdset(wfd, &efd_set);
/* Check for notifier FD readability. */
if (notify_rfd != INVALID_SOCKET) {
openssl_fdset(notify_rfd, &rfd_set);
openssl_fdset(notify_rfd, &efd_set);
}
maxfd = rfd;
if (wfd > maxfd)
maxfd = wfd;
if (notify_rfd > maxfd)
maxfd = notify_rfd;
if (!ossl_assert(rfd != INVALID_SOCKET || wfd != INVALID_SOCKET
|| !ossl_time_is_infinite(deadline)))
/* Do not block forever; should not happen. */
return 0;
/*
* The mutex dance (unlock/re-locak after poll/seclect) is
* potentially problematic. This may create a situation when
* two threads arrive to select/poll with the same file
* descriptors. We just need to be aware of this.
*/
# if defined(OPENSSL_THREADS)
if (mutex != NULL)
ossl_crypto_mutex_unlock(mutex);
# endif
do {
/*
* select expects a timeout, not a deadline, so do the conversion.
* Update for each call to ensure the correct value is used if we repeat
* due to EINTR.
*/
if (ossl_time_is_infinite(deadline)) {
ptv = NULL;
} else {
now = ossl_time_now();
/*
* ossl_time_subtract saturates to zero so we don't need to check if
* now > deadline.
*/
timeout = ossl_time_subtract(deadline, now);
tv = ossl_time_to_timeval(timeout);
ptv = &tv;
}
pres = select(maxfd + 1, &rfd_set, &wfd_set, &efd_set, ptv);
} while (pres == -1 && get_last_socket_error_is_eintr());
# if defined(OPENSSL_THREADS)
if (mutex != NULL)
ossl_crypto_mutex_lock(mutex);
# endif
return pres < 0 ? 0 : 1;
#else
int pres, timeout_ms;
OSSL_TIME now, timeout;
struct pollfd pfds[3] = {0};
size_t npfd = 0;
if (rfd == wfd) {
pfds[npfd].fd = rfd;
pfds[npfd].events = (rfd_want_read ? POLLIN : 0)
| (wfd_want_write ? POLLOUT : 0);
if (rfd >= 0 && pfds[npfd].events != 0)
++npfd;
} else {
pfds[npfd].fd = rfd;
pfds[npfd].events = (rfd_want_read ? POLLIN : 0);
if (rfd >= 0 && pfds[npfd].events != 0)
++npfd;
pfds[npfd].fd = wfd;
pfds[npfd].events = (wfd_want_write ? POLLOUT : 0);
if (wfd >= 0 && pfds[npfd].events != 0)
++npfd;
}
if (notify_rfd >= 0) {
pfds[npfd].fd = notify_rfd;
pfds[npfd].events = POLLIN;
++npfd;
}
if (!ossl_assert(npfd != 0 || !ossl_time_is_infinite(deadline)))
/* Do not block forever; should not happen. */
return 0;
# if defined(OPENSSL_THREADS)
if (mutex != NULL)
ossl_crypto_mutex_unlock(mutex);
# endif
do {
if (ossl_time_is_infinite(deadline)) {
timeout_ms = -1;
} else {
now = ossl_time_now();
timeout = ossl_time_subtract(deadline, now);
timeout_ms = ossl_time2ms(timeout);
}
pres = poll(pfds, npfd, timeout_ms);
} while (pres == -1 && get_last_socket_error_is_eintr());
# if defined(OPENSSL_THREADS)
if (mutex != NULL)
ossl_crypto_mutex_lock(mutex);
# endif
return pres < 0 ? 0 : 1;
#endif
}
static int poll_descriptor_to_fd(const BIO_POLL_DESCRIPTOR *d, int *fd)
{
if (d == NULL || d->type == BIO_POLL_DESCRIPTOR_TYPE_NONE) {
*fd = INVALID_SOCKET;
return 1;
}
if (d->type != BIO_POLL_DESCRIPTOR_TYPE_SOCK_FD
|| d->value.fd == INVALID_SOCKET)
return 0;
*fd = d->value.fd;
return 1;
}
/*
* Poll up to two abstract poll descriptors, as well as an optional notify FD.
* Currently we only support poll descriptors which represent FDs.
*
* If mutex is non-NULL, it is assumed be a lock currently held for write and is
* unlocked for the duration of any wait.
*
* Precondition: mutex is NULL or is held for write (unchecked)
* Postcondition: mutex is NULL or is held for write (unless
* CRYPTO_THREAD_write_lock fails)
*/
static int poll_two_descriptors(const BIO_POLL_DESCRIPTOR *r, int r_want_read,
const BIO_POLL_DESCRIPTOR *w, int w_want_write,
int notify_rfd,
OSSL_TIME deadline,
CRYPTO_MUTEX *mutex)
{
int rfd, wfd;
if (!poll_descriptor_to_fd(r, &rfd)
|| !poll_descriptor_to_fd(w, &wfd))
return 0;
return poll_two_fds(rfd, r_want_read, wfd, w_want_write,
notify_rfd, deadline, mutex);
}
/*
* Notify other threads currently blocking in
* ossl_quic_reactor_block_until_pred() calls that a predicate they are using
* might now be met due to state changes.
*
* This function must be called after state changes which might cause a
* predicate in another thread to now be met (i.e., ticking). It is a no-op if
* inter-thread notification is not being used.
*
* The reactor mutex must be held while calling this function.
*/
static void rtor_notify_other_threads(QUIC_REACTOR *rtor)
{
if (!rtor->have_notifier)
return;
/*
* This function is called when we have done anything on this thread which
* might allow a predicate for a block_until_pred call on another thread to
* now be met.
*
* When this happens, we need to wake those threads using the notifier.
* However, we do not want to wake *this* thread (if/when it subsequently
* enters block_until_pred) due to the notifier FD becoming readable.
* Therefore, signal the notifier, and use a CV to detect when all other
* threads have woken.
*/
if (rtor->cur_blocking_waiters == 0)
/* Nothing to do in this case. */
return;
/* Signal the notifier to wake up all threads. */
if (!rtor->signalled_notifier) {
ossl_rio_notifier_signal(&rtor->notifier);
rtor->signalled_notifier = 1;
}
/*
* Wait on the CV until all threads have finished the first phase of the
* wakeup process and the last thread out has taken responsibility for
* unsignalling the notifier.
*/
while (rtor->signalled_notifier)
ossl_crypto_condvar_wait(rtor->notifier_cv, rtor->mutex);
}
/*
* Block until a predicate function evaluates to true.
*
* If mutex is non-NULL, it is assumed be a lock currently held for write and is
* unlocked for the duration of any wait.
*
* Precondition: Must hold channel write lock (unchecked)
* Precondition: mutex is NULL or is held for write (unchecked)
* Postcondition: mutex is NULL or is held for write (unless
* CRYPTO_THREAD_write_lock fails)
*/
int ossl_quic_reactor_block_until_pred(QUIC_REACTOR *rtor,
int (*pred)(void *arg), void *pred_arg,
uint32_t flags)
{
int res, net_read_desired, net_write_desired, notifier_fd;
OSSL_TIME tick_deadline;
notifier_fd
= (rtor->have_notifier ? ossl_rio_notifier_as_fd(&rtor->notifier)
: INVALID_SOCKET);
for (;;) {
if ((flags & SKIP_FIRST_TICK) != 0)
flags &= ~SKIP_FIRST_TICK;
else
/* best effort */
ossl_quic_reactor_tick(rtor, 0);
if ((res = pred(pred_arg)) != 0)
return res;
net_read_desired = ossl_quic_reactor_net_read_desired(rtor);
net_write_desired = ossl_quic_reactor_net_write_desired(rtor);
tick_deadline = ossl_quic_reactor_get_tick_deadline(rtor);
if (!net_read_desired && !net_write_desired
&& ossl_time_is_infinite(tick_deadline))
/* Can't wait if there is nothing to wait for. */
return 0;
ossl_quic_reactor_enter_blocking_section(rtor);
res = poll_two_descriptors(ossl_quic_reactor_get_poll_r(rtor),
net_read_desired,
ossl_quic_reactor_get_poll_w(rtor),
net_write_desired,
notifier_fd,
tick_deadline,
rtor->mutex);
/*
* We have now exited the OS poller call. We may have
* (rtor->signalled_notifier), and other threads may still be blocking.
* This means that cur_blocking_waiters may still be non-zero. As such,
* we cannot unsignal the notifier until all threads have had an
* opportunity to wake up.
*
* At the same time, we cannot unsignal in the case where
* cur_blocking_waiters is now zero because this condition may not occur
* reliably. Consider the following scenario:
*
* T1 enters block_until_pred, cur_blocking_waiters -> 1
* T2 enters block_until_pred, cur_blocking_waiters -> 2
* T3 enters block_until_pred, cur_blocking_waiters -> 3
*
* T4 enters block_until_pred, does not block, ticks,
* sees that cur_blocking_waiters > 0 and signals the notifier
*
* T3 wakes, cur_blocking_waiters -> 2
* T3 predicate is not satisfied, cur_blocking_waiters -> 3, block again
*
* Notifier is still signalled, so T3 immediately wakes again
* and is stuck repeating the above steps.
*
* T1, T2 are also woken by the notifier but never see
* cur_blocking_waiters drop to 0, so never unsignal the notifier.
*
* As such, a two phase approach is chosen when designalling the
* notifier:
*
* First, all of the poll_two_descriptor calls on all threads are
* allowed to exit due to the notifier being signalled.
*
* Second, the thread which happened to be the one which decremented
* cur_blocking_waiters to 0 unsignals the notifier and is then
* responsible for broadcasting to a CV to indicate to the other
* threads that the synchronised wakeup has been completed. Other
* threads wait for this CV to be signalled.
*
*/
ossl_quic_reactor_leave_blocking_section(rtor);
if (!res)
/*
* We don't actually care why the call succeeded (timeout, FD
* readiness), we just call reactor_tick and start trying to do I/O
* things again. If poll_two_fds returns 0, this is some other
* non-timeout failure and we should stop here.
*
* TODO(QUIC FUTURE): In the future we could avoid unnecessary
* syscalls by not retrying network I/O that isn't ready based
* on the result of the poll call. However this might be difficult
* because it requires we do the call to poll(2) or equivalent
* syscall ourselves, whereas in the general case the application
* does the polling and just calls SSL_handle_events().
* Implementing this optimisation in the future will probably
* therefore require API changes.
*/
return 0;
}
return res;
}
void ossl_quic_reactor_enter_blocking_section(QUIC_REACTOR *rtor)
{
++rtor->cur_blocking_waiters;
}
void ossl_quic_reactor_leave_blocking_section(QUIC_REACTOR *rtor)
{
assert(rtor->cur_blocking_waiters > 0);
--rtor->cur_blocking_waiters;
if (rtor->have_notifier && rtor->signalled_notifier) {
if (rtor->cur_blocking_waiters == 0) {
ossl_rio_notifier_unsignal(&rtor->notifier);
rtor->signalled_notifier = 0;
/*
* Release the other threads which have woken up (and possibly
* rtor_notify_other_threads as well).
*/
ossl_crypto_condvar_broadcast(rtor->notifier_cv);
} else {
/* We are not the last waiter out - so wait for that one. */
while (rtor->signalled_notifier)
ossl_crypto_condvar_wait(rtor->notifier_cv, rtor->mutex);
}
}
}
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