1 /*
2 * Copyright 2022-2025 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9 #ifndef OSSL_QUIC_REACTOR_H
10 # define OSSL_QUIC_REACTOR_H
11
12 # include "internal/time.h"
13 # include "internal/sockets.h"
14 # include "internal/quic_predef.h"
15 # include "internal/thread_arch.h"
16 # include "internal/rio_notifier.h"
17 # include <openssl/bio.h>
18
19 # ifndef OPENSSL_NO_QUIC
20
21 /*
22 * Core I/O Reactor Framework
23 * ==========================
24 *
25 * Manages use of async network I/O which the QUIC stack is built on. The core
26 * mechanic looks like this:
27 *
28 * - There is a pollable FD for both the read and write side respectively.
29 * Readability and writeability of these FDs respectively determines when
30 * network I/O is available.
31 *
32 * - The reactor can export these FDs to the user, as well as flags indicating
33 * whether the user should listen for readability, writeability, or neither.
34 *
35 * - The reactor can export a timeout indication to the user, indicating when
36 * the reactor should be called (via libssl APIs) regardless of whether
37 * the network socket has become ready.
38 *
39 * The reactor is based around a tick callback which is essentially the mutator
40 * function. The mutator attempts to do whatever it can, attempting to perform
41 * network I/O to the extent currently feasible. When done, the mutator returns
42 * information to the reactor indicating when it should be woken up again:
43 *
44 * - Should it be woken up when network RX is possible?
45 * - Should it be woken up when network TX is possible?
46 * - Should it be woken up no later than some deadline X?
47 *
48 * The intention is that ALL I/O-related SSL_* functions with side effects (e.g.
49 * SSL_read/SSL_write) consist of three phases:
50 *
51 * - Optionally mutate the QUIC machine's state.
52 * - Optionally tick the QUIC reactor.
53 * - Optionally mutate the QUIC machine's state.
54 *
55 * For example, SSL_write is a mutation (appending to a stream buffer) followed
56 * by an optional tick (generally expected as we may want to send the data
57 * immediately, though not strictly needed if transmission is being deferred due
58 * to Nagle's algorithm, etc.).
59 *
60 * SSL_read is also a mutation and in principle does not need to tick the
61 * reactor, but it generally will anyway to ensure that the reactor is regularly
62 * ticked by an application which is only reading and not writing.
63 *
64 * If the SSL object is being used in blocking mode, SSL_read may need to block
65 * if no data is available yet, and SSL_write may need to block if buffers
66 * are full.
67 *
68 * The internals of the QUIC I/O engine always use asynchronous I/O. If the
69 * application desires blocking semantics, we handle this by adding a blocking
70 * adaptation layer on top of our internal asynchronous I/O API as exposed by
71 * the reactor interface.
72 */
73 struct quic_tick_result_st {
74 OSSL_TIME tick_deadline;
75 char net_read_desired;
76 char net_write_desired;
77 char notify_other_threads;
78 };
79
80 static ossl_inline ossl_unused void
ossl_quic_tick_result_merge_into(QUIC_TICK_RESULT * r,const QUIC_TICK_RESULT * src)81 ossl_quic_tick_result_merge_into(QUIC_TICK_RESULT *r,
82 const QUIC_TICK_RESULT *src)
83 {
84 r->net_read_desired = r->net_read_desired || src->net_read_desired;
85 r->net_write_desired = r->net_write_desired || src->net_write_desired;
86 r->notify_other_threads = r->notify_other_threads || src->notify_other_threads;
87 r->tick_deadline = ossl_time_min(r->tick_deadline, src->tick_deadline);
88 }
89
90 struct quic_reactor_st {
91 /*
92 * BIO poll descriptors which can be polled. poll_r is a poll descriptor
93 * which becomes readable when the QUIC state machine can potentially do
94 * work, and poll_w is a poll descriptor which becomes writable when the
95 * QUIC state machine can potentially do work. Generally, either of these
96 * conditions means that SSL_tick() should be called, or another SSL
97 * function which implicitly calls SSL_tick() (e.g. SSL_read/SSL_write()).
98 */
99 BIO_POLL_DESCRIPTOR poll_r, poll_w;
100 OSSL_TIME tick_deadline; /* ossl_time_infinite() if none currently applicable */
101
102 void (*tick_cb)(QUIC_TICK_RESULT *res, void *arg, uint32_t flags);
103 void *tick_cb_arg;
104
105 /* The mutex used for ticking. Not owned by the reactor. */
106 CRYPTO_MUTEX *mutex;
107
108 /* Used to notify other threads. Valid only if have_notifier is set. */
109 RIO_NOTIFIER notifier;
110
111 /*
112 * Condvar to assist synchronising use of the notifier. Valid only if
113 * have_notifier is set.
114 */
115 CRYPTO_CONDVAR *notifier_cv;
116
117 /*
118 * Count of the current number of blocking waiters. Like everything else,
119 * this is protected by the caller's mutex (i.e., the engine mutex).
120 */
121 size_t cur_blocking_waiters;
122
123 /*
124 * These are true if we would like to know when we can read or write from
125 * the network respectively.
126 */
127 unsigned int net_read_desired : 1;
128 unsigned int net_write_desired : 1;
129
130 /*
131 * Are the read and write poll descriptors we are currently configured with
132 * things we can actually poll?
133 */
134 unsigned int can_poll_r : 1;
135 unsigned int can_poll_w : 1;
136
137 /* 1 if notifier is present and initialised. */
138 unsigned int have_notifier : 1;
139
140 /* 1 if a block_until_pred call has put the notifier in the signalled state. */
141 unsigned int signalled_notifier : 1;
142 };
143
144 /* Create an OS notifier? */
145 #define QUIC_REACTOR_FLAG_USE_NOTIFIER (1U << 0)
146
147 int ossl_quic_reactor_init(QUIC_REACTOR *rtor,
148 void (*tick_cb)(QUIC_TICK_RESULT *res, void *arg,
149 uint32_t flags),
150 void *tick_cb_arg,
151 CRYPTO_MUTEX *mutex,
152 OSSL_TIME initial_tick_deadline,
153 uint64_t flags);
154
155 void ossl_quic_reactor_cleanup(QUIC_REACTOR *rtor);
156
157 void ossl_quic_reactor_set_poll_r(QUIC_REACTOR *rtor,
158 const BIO_POLL_DESCRIPTOR *r);
159
160 void ossl_quic_reactor_set_poll_w(QUIC_REACTOR *rtor,
161 const BIO_POLL_DESCRIPTOR *w);
162
163 const BIO_POLL_DESCRIPTOR *ossl_quic_reactor_get_poll_r(const QUIC_REACTOR *rtor);
164 const BIO_POLL_DESCRIPTOR *ossl_quic_reactor_get_poll_w(const QUIC_REACTOR *rtor);
165
166 int ossl_quic_reactor_can_poll_r(const QUIC_REACTOR *rtor);
167 int ossl_quic_reactor_can_poll_w(const QUIC_REACTOR *rtor);
168
169 int ossl_quic_reactor_can_support_poll_descriptor(const QUIC_REACTOR *rtor,
170 const BIO_POLL_DESCRIPTOR *d);
171
172 int ossl_quic_reactor_net_read_desired(QUIC_REACTOR *rtor);
173 int ossl_quic_reactor_net_write_desired(QUIC_REACTOR *rtor);
174
175 OSSL_TIME ossl_quic_reactor_get_tick_deadline(QUIC_REACTOR *rtor);
176
177 /*
178 * Do whatever work can be done, and as much work as can be done. This involves
179 * e.g. seeing if we can read anything from the network (if we want to), seeing
180 * if we can write anything to the network (if we want to), etc.
181 *
182 * If the CHANNEL_ONLY flag is set, this indicates that we should only
183 * touch state which is synchronised by the channel mutex.
184 */
185 #define QUIC_REACTOR_TICK_FLAG_CHANNEL_ONLY (1U << 0)
186
187 int ossl_quic_reactor_tick(QUIC_REACTOR *rtor, uint32_t flags);
188
189 RIO_NOTIFIER *ossl_quic_reactor_get0_notifier(QUIC_REACTOR *rtor);
190
191 /*
192 * Blocking I/O Adaptation Layer
193 * =============================
194 *
195 * The blocking I/O adaptation layer implements blocking I/O on top of our
196 * asynchronous core.
197 */
198
199 /*
200 * ossl_quic_reactor_block_until_pred
201 * ----------------------------------
202 *
203 * The core mechanism of the Blocking I/O Adaption Layer is block_until_pred(),
204 * which does not return until pred() returns a value other than 0. The blocker
205 * uses OS I/O synchronisation primitives (e.g. poll(2)) and ticks the reactor
206 * until the predicate is satisfied. The blocker is not required to call pred()
207 * more than once between tick calls.
208 *
209 * When pred returns a non-zero value, that value is returned by this function.
210 * This can be used to allow pred() to indicate error conditions and short
211 * circuit the blocking process.
212 *
213 * A return value of -1 is reserved for network polling errors. Therefore this
214 * return value should not be used by pred() if ambiguity is not desired. Note
215 * that the predicate function can always arrange its own output mechanism, for
216 * example by passing a structure of its own as the argument.
217 *
218 * If the SKIP_FIRST_TICK flag is set, the first call to reactor_tick() before
219 * the first call to pred() is skipped. This is useful if it is known that
220 * ticking the reactor again will not be useful (e.g. because it has already
221 * been done).
222 *
223 * This function assumes a write lock is held for the entire QUIC_CHANNEL. If
224 * mutex is non-NULL, it must be a lock currently held for write; it will be
225 * unlocked during any sleep, and then relocked for write afterwards.
226 *
227 * This function must not be called by a thread currently using
228 * ossl_quic_reactor_(enter/leave)_blocking_section() as this function also uses
229 * those functions (see below); it is assumed if a caller is using those
230 * functions it is implementing blocking semantics itself. There is no need to
231 * use those functions if using this function.
232 *
233 * Precondition: If a reactor mutex is being used, it must be held (unchecked)
234 * Postcondition: If a reactor mutex is being used, it is held
235 * Invariant: The current thread does not have an outstanding
236 * ossl_quic_reactor_enter_blocking_section() call (unchecked)
237 */
238 #define SKIP_FIRST_TICK (1U << 0)
239
240 int ossl_quic_reactor_block_until_pred(QUIC_REACTOR *rtor,
241 int (*pred)(void *arg), void *pred_arg,
242 uint32_t flags);
243
244 /*
245 * ossl_quic_reactor_(enter/leave)_blocking_section
246 * ------------------------------------------------
247 *
248 * This is used by blocking code outside of the reactor itself to inform the
249 * reactor of when a thread begins or ends a blocking call. This is used by the
250 * reactor so it knows if a tick means other threads might need to be woken up
251 * via the notifier. The reactor mutex must be held while calling these
252 * functions.
253 *
254 * The number of 'active' calls to these functions (i.e., the number of enter
255 * calls which have yet to be matched with a subsequent leave call) must *at all
256 * times* equal the number of threads blocking on the reactor. In other words, a
257 * single thread is not permitted to use these functions "recursively". Failing
258 * to adhere to this rule will result in deadlock.
259 *
260 * This means that if a caller has the concept of multiple concurrent blocking
261 * calls on the same thread on the same reactor (which may occur in some
262 * SSL_poll-related circumstances) it must do its own housekeeping to ensure it
263 * only calls enter() once. See quic_reactor_wait_ctx.h for a utility which can
264 * be used to accomplish this.
265 *
266 * ossl_quic_reactor_enter_blocking_section:
267 * Precondition: The current thread does not have an outstanding
268 * ossl_quic_reactor_enter_blocking_section() call (unchecked)
269 * Postcondition: The current thread has an outstanding
270 * ossl_quic_reactor_enter_blocking_section() call
271 *
272 * ossl_quic_reactor_leave_blocking_section:
273 * Precondition: The current thread has an outstanding
274 * ossl_quic_reactor_enter_blocking_section() call (unchecked)
275 * Postcondition: The current thread does not have an outstanding
276 * ossl_quic_reactor_enter_blocking_section() call
277 *
278 */
279 void ossl_quic_reactor_enter_blocking_section(QUIC_REACTOR *rtor);
280 void ossl_quic_reactor_leave_blocking_section(QUIC_REACTOR *rtor);
281
282 # endif
283
284 #endif
285