1/* Copyright (C) 2001-2021 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Ulrich Drepper <drepper@redhat.com>, 2001.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <assert.h>
20#include <errno.h>
21#include <pthread.h>
22#include <stdlib.h>
23#include <sys/time.h>
24
25#include <gai_misc.h>
26
27
28
29#ifndef gai_create_helper_thread
30# define gai_create_helper_thread __gai_create_helper_thread
31
32extern inline int
33__gai_create_helper_thread (pthread_t *threadp, void *(*tf) (void *),
34 void *arg)
35{
36 pthread_attr_t attr;
37
38 /* Make sure the thread is created detached. */
39 pthread_attr_init (&attr);
40 pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
41
42 int ret = pthread_create (threadp, &attr, tf, arg);
43
44 (void) pthread_attr_destroy (&attr);
45 return ret;
46}
47#endif
48
49
50/* Pool of request list entries. */
51static struct requestlist **pool;
52
53/* Number of total and allocated pool entries. */
54static size_t pool_max_size;
55static size_t pool_size;
56
57/* We implement a two dimensional array but allocate each row separately.
58 The macro below determines how many entries should be used per row.
59 It should better be a power of two. */
60#define ENTRIES_PER_ROW 32
61
62/* How many rows we allocate at once. */
63#define ROWS_STEP 8
64
65/* List of available entries. */
66static struct requestlist *freelist;
67
68/* Structure list of all currently processed requests. */
69static struct requestlist *requests;
70static struct requestlist *requests_tail;
71
72/* Number of threads currently running. */
73static int nthreads;
74
75/* Number of threads waiting for work to arrive. */
76static int idle_thread_count;
77
78
79/* These are the values used for optimization. We will probably
80 create a funcion to set these values. */
81static struct gaiinit optim =
82{
83 20, /* int gai_threads; Maximal number of threads. */
84 64, /* int gai_num; Number of expected simultanious requests. */
85 0,
86 0,
87 0,
88 0,
89 1,
90 0
91};
92
93
94/* Since the list is global we need a mutex protecting it. */
95pthread_mutex_t __gai_requests_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
96
97/* When you add a request to the list and there are idle threads present,
98 you signal this condition variable. When a thread finishes work, it waits
99 on this condition variable for a time before it actually exits. */
100pthread_cond_t __gai_new_request_notification = PTHREAD_COND_INITIALIZER;
101
102
103/* Functions to handle request list pool. */
104static struct requestlist *
105get_elem (void)
106{
107 struct requestlist *result;
108
109 if (freelist == NULL)
110 {
111 struct requestlist *new_row;
112 int cnt;
113
114 if (pool_size + 1 >= pool_max_size)
115 {
116 size_t new_max_size = pool_max_size + ROWS_STEP;
117 struct requestlist **new_tab;
118
119 new_tab = (struct requestlist **)
120 realloc (pool, new_max_size * sizeof (struct requestlist *));
121
122 if (new_tab == NULL)
123 return NULL;
124
125 pool_max_size = new_max_size;
126 pool = new_tab;
127 }
128
129 /* Allocate the new row. */
130 cnt = pool_size == 0 ? optim.gai_num : ENTRIES_PER_ROW;
131 new_row = (struct requestlist *) calloc (cnt,
132 sizeof (struct requestlist));
133 if (new_row == NULL)
134 return NULL;
135
136 pool[pool_size++] = new_row;
137
138 /* Put all the new entries in the freelist. */
139 do
140 {
141 new_row->next = freelist;
142 freelist = new_row++;
143 }
144 while (--cnt > 0);
145 }
146
147 result = freelist;
148 freelist = freelist->next;
149
150 return result;
151}
152
153
154struct requestlist *
155__gai_find_request (const struct gaicb *gaicbp)
156{
157 struct requestlist *runp;
158
159 runp = requests;
160 while (runp != NULL)
161 if (runp->gaicbp == gaicbp)
162 return runp;
163 else
164 runp = runp->next;
165
166 return NULL;
167}
168
169
170int
171__gai_remove_request (struct gaicb *gaicbp)
172{
173 struct requestlist *runp;
174 struct requestlist *lastp;
175
176 runp = requests;
177 lastp = NULL;
178 while (runp != NULL)
179 if (runp->gaicbp == gaicbp)
180 break;
181 else
182 {
183 lastp = runp;
184 runp = runp->next;
185 }
186
187 if (runp == NULL)
188 /* Not known. */
189 return -1;
190 if (runp->running != 0)
191 /* Currently handled. */
192 return 1;
193
194 /* Dequeue the request. */
195 if (lastp == NULL)
196 requests = runp->next;
197 else
198 lastp->next = runp->next;
199 if (runp == requests_tail)
200 requests_tail = lastp;
201
202 return 0;
203}
204
205
206/* The thread handler. */
207static void *handle_requests (void *arg);
208
209
210/* The main function of the async I/O handling. It enqueues requests
211 and if necessary starts and handles threads. */
212struct requestlist *
213__gai_enqueue_request (struct gaicb *gaicbp)
214{
215 struct requestlist *newp;
216 struct requestlist *lastp;
217
218 /* Get the mutex. */
219 pthread_mutex_lock (&__gai_requests_mutex);
220
221 /* Get a new element for the waiting list. */
222 newp = get_elem ();
223 if (newp == NULL)
224 {
225 pthread_mutex_unlock (&__gai_requests_mutex);
226 __set_errno (EAGAIN);
227 return NULL;
228 }
229 newp->running = 0;
230 newp->gaicbp = gaicbp;
231 newp->waiting = NULL;
232 newp->next = NULL;
233
234 lastp = requests_tail;
235 if (requests_tail == NULL)
236 requests = requests_tail = newp;
237 else
238 {
239 requests_tail->next = newp;
240 requests_tail = newp;
241 }
242
243 gaicbp->__return = EAI_INPROGRESS;
244
245 /* See if we need to and are able to create a thread. */
246 if (nthreads < optim.gai_threads && idle_thread_count == 0)
247 {
248 pthread_t thid;
249
250 newp->running = 1;
251
252 /* Now try to start a thread. */
253 if (gai_create_helper_thread (&thid, handle_requests, newp) == 0)
254 /* We managed to enqueue the request. All errors which can
255 happen now can be recognized by calls to `gai_error'. */
256 ++nthreads;
257 else
258 {
259 if (nthreads == 0)
260 {
261 /* We cannot create a thread in the moment and there is
262 also no thread running. This is a problem. `errno' is
263 set to EAGAIN if this is only a temporary problem. */
264 assert (requests == newp || lastp->next == newp);
265 if (lastp != NULL)
266 lastp->next = NULL;
267 else
268 requests = NULL;
269 requests_tail = lastp;
270
271 newp->next = freelist;
272 freelist = newp;
273
274 newp = NULL;
275 }
276 else
277 /* We are not handling the request after all. */
278 newp->running = 0;
279 }
280 }
281
282 /* Enqueue the request in the request queue. */
283 if (newp != NULL)
284 {
285 /* If there is a thread waiting for work, then let it know that we
286 have just given it something to do. */
287 if (idle_thread_count > 0)
288 pthread_cond_signal (&__gai_new_request_notification);
289 }
290
291 /* Release the mutex. */
292 pthread_mutex_unlock (&__gai_requests_mutex);
293
294 return newp;
295}
296
297
298static void *
299__attribute__ ((noreturn))
300handle_requests (void *arg)
301{
302 struct requestlist *runp = (struct requestlist *) arg;
303
304 do
305 {
306 /* If runp is NULL, then we were created to service the work queue
307 in general, not to handle any particular request. In that case we
308 skip the "do work" stuff on the first pass, and go directly to the
309 "get work off the work queue" part of this loop, which is near the
310 end. */
311 if (runp == NULL)
312 pthread_mutex_lock (&__gai_requests_mutex);
313 else
314 {
315 /* Make the request. */
316 struct gaicb *req = runp->gaicbp;
317 struct requestlist *srchp;
318 struct requestlist *lastp;
319
320 req->__return = getaddrinfo (req->ar_name, req->ar_service,
321 req->ar_request, &req->ar_result);
322
323 /* Get the mutex. */
324 pthread_mutex_lock (&__gai_requests_mutex);
325
326 /* Send the signal to notify about finished processing of the
327 request. */
328 __gai_notify (runp);
329
330 /* Now dequeue the current request. */
331 lastp = NULL;
332 srchp = requests;
333 while (srchp != runp)
334 {
335 lastp = srchp;
336 srchp = srchp->next;
337 }
338 assert (runp->running == 1);
339
340 if (requests_tail == runp)
341 requests_tail = lastp;
342 if (lastp == NULL)
343 requests = requests->next;
344 else
345 lastp->next = runp->next;
346
347 /* Free the old element. */
348 runp->next = freelist;
349 freelist = runp;
350 }
351
352 runp = requests;
353 while (runp != NULL && runp->running != 0)
354 runp = runp->next;
355
356 /* If the runlist is empty, then we sleep for a while, waiting for
357 something to arrive in it. */
358 if (runp == NULL && optim.gai_idle_time >= 0)
359 {
360 struct timespec now;
361 struct timespec wakeup_time;
362
363 ++idle_thread_count;
364 __clock_gettime (CLOCK_REALTIME, &now);
365 wakeup_time.tv_sec = now.tv_sec + optim.gai_idle_time;
366 wakeup_time.tv_nsec = now.tv_nsec;
367 if (wakeup_time.tv_nsec >= 1000000000)
368 {
369 wakeup_time.tv_nsec -= 1000000000;
370 ++wakeup_time.tv_sec;
371 }
372 pthread_cond_timedwait (&__gai_new_request_notification,
373 &__gai_requests_mutex, &wakeup_time);
374 --idle_thread_count;
375 runp = requests;
376 while (runp != NULL && runp->running != 0)
377 runp = runp->next;
378 }
379
380 if (runp == NULL)
381 --nthreads;
382 else
383 {
384 /* Mark the request as being worked on. */
385 assert (runp->running == 0);
386 runp->running = 1;
387
388 /* If we have a request to process, and there's still another in
389 the run list, then we need to either wake up or create a new
390 thread to service the request that is still in the run list. */
391 if (requests != NULL)
392 {
393 /* There are at least two items in the work queue to work on.
394 If there are other idle threads, then we should wake them
395 up for these other work elements; otherwise, we should try
396 to create a new thread. */
397 if (idle_thread_count > 0)
398 pthread_cond_signal (&__gai_new_request_notification);
399 else if (nthreads < optim.gai_threads)
400 {
401 pthread_t thid;
402 pthread_attr_t attr;
403
404 /* Make sure the thread is created detached. */
405 pthread_attr_init (&attr);
406 pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
407
408 /* Now try to start a thread. If we fail, no big deal,
409 because we know that there is at least one thread (us)
410 that is working on lookup operations. */
411 if (pthread_create (&thid, &attr, handle_requests, NULL)
412 == 0)
413 ++nthreads;
414 }
415 }
416 }
417
418 /* Release the mutex. */
419 pthread_mutex_unlock (&__gai_requests_mutex);
420 }
421 while (runp != NULL);
422
423 pthread_exit (NULL);
424}
425
426
427/* Free allocated resources. */
428libc_freeres_fn (free_res)
429{
430 size_t row;
431
432 for (row = 0; row < pool_max_size; ++row)
433 free (pool[row]);
434
435 free (pool);
436}
437