Memcached源码分析之items.c

1. #include "memcached.h"
2. #include <sys/stat.h>
3. #include <sys/socket.h>
4. #include <sys/signal.h>
5. #include <sys/resource.h>
6. #include <fcntl.h>
7. #include <netinet/in.h>
8. #include <errno.h>
9. #include <stdlib.h>
10. #include <stdio.h>
11. #include <string.h>
12. #include <time.h>
13. #include <assert.h>
14. #include <unistd.h>
15. static void item_link_q(item *it);
16. static void item_unlink_q(item *it);
17. #define LARGEST_ID POWER_LARGEST
18. typedef struct {
19. uint64_t evicted;
20. uint64_t evicted_nonzero;
21. rel_time_t evicted_time;
22. uint64_t reclaimed;
23. uint64_t outofmemory;
24. uint64_t tailrepairs;
25. uint64_t expired_unfetched;
26. uint64_t evicted_unfetched;
27. uint64_t crawler_reclaimed;
28. } itemstats_t;
29. static item *heads[LARGEST_ID]; //各个slabclass的LRU队列头指针数组
30. static item *tails[LARGEST_ID]; //各个slabclass的LRU队列尾指针数组
31. static crawler crawlers[LARGEST_ID]; //各个slabclass的item爬虫数组
32. static itemstats_t itemstats[LARGEST_ID]; //各个slabclass的item统计数组
33. static unsigned int sizes[LARGEST_ID]; //各个slabclass的chunk大小数组
34. static int crawler_count = 0;
35. static volatile int do_run_lru_crawler_thread = 0;
36. static int lru_crawler_initialized = 0;
37. static pthread_mutex_t lru_crawler_lock = PTHREAD_MUTEX_INITIALIZER;
38. static pthread_cond_t lru_crawler_cond = PTHREAD_COND_INITIALIZER;
39. //重置统计
40. void item_stats_reset(void) {
41. mutex_lock(&cache_lock);
42. memset(itemstats, 0, sizeof(itemstats));
43. mutex_unlock(&cache_lock);
44. }
45. /* Get the next CAS id for a new item. */
46. uint64_t get_cas_id(void) {
47. static uint64_t cas_id = 0;
48. return ++cas_id;
49. }
50. /* Enable this for reference-count debugging. */
51. #if 0
52. # define DEBUG_REFCNT(it,op) \
53. fprintf(stderr, "item %x refcnt(%c) %d %c%c%c\n", \
54. it, op, it->refcount, \
55. (it->it_flags & ITEM_LINKED) ? 'L' : ' ', \
56. (it->it_flags & ITEM_SLABBED) ? 'S' : ' ')
57. #else
58. # define DEBUG_REFCNT(it,op) while(0)
59. #endif
60. /**
61. 算出item总大小
62. */
63. static size_t item_make_header(const uint8_t nkey, const int flags, const int nbytes,
64. char *suffix, uint8_t *nsuffix) {
65. /* suffix is defined at 40 chars elsewhere.. */
66. *nsuffix = (uint8_t) snprintf(suffix, 40, " %d %d\r\n", flags, nbytes - 2);
67. return sizeof(item) + nkey + *nsuffix + nbytes;
68. }
69. /**
70. item分配
71. 把这个函数弄清楚，基本就把memcached内存管理机制大体弄清楚了。
72. */
73. item *do_item_alloc(char *key, const size_t nkey, const int flags,
74. const rel_time_t exptime, const int nbytes,
75. const uint32_t cur_hv) {
76. uint8_t nsuffix;
77. item *it = NULL;
78. char suffix[40];
79. size_t ntotal = item_make_header(nkey + 1, flags, nbytes, suffix, &nsuffix); //item总大小
80. if (settings.use_cas) {
81. ntotal += sizeof(uint64_t); //如果有用到cas 那么item大小还要加上unit64_t的size
82. }
83. unsigned int id = slabs_clsid(ntotal); //根据item大小，找到适合的slabclass
84. if (id == 0)
85. return 0;
86. mutex_lock(&cache_lock); //cache锁
87. /* do a quick check if we have any expired items in the tail.. */
88. /* 准备分配新的item了，随便快速瞄一下lru链表末尾有没有过期item，有的话就用过期的空间 */
89. int tries = 5;
90. int tried_alloc = 0;
91. item *search;
92. void *hold_lock = NULL;
93. rel_time_t oldest_live = settings.oldest_live;
94. search = tails[id]; //这个tails是一个全局变量，tails[xx]是id为xx的slabclass lru链表的尾部
95. /* We walk up *only* for locked items. Never searching for expired.
96. * Waste of CPU for almost all deployments */
97. //从LRU链表尾部（就是最久没使用过的item）开始往前找
98. for (; tries > 0 && search != NULL; tries--, search=search->prev) {
99. if (search->nbytes == 0 && search->nkey == 0 && search->it_flags == 1) {
100. /* We are a crawler, ignore it. */
101. /*
102. 这里注释意思是说我们现在是以爬虫的身份来爬出过期的空间，
103. 像爬到这种很怪的item，就别管了，不是爬虫要做的事，不要就行了。
104. */
105. tries++;
106. continue;
107. }
108. /**
109. 你会看到很多地方有这个hv，简单说下，其实它是对item的一个hash，得到hv值，这个hv主要有两个
110. 作用：
111. 1）用于hash表保存item，通过hv计算出哈希表中的桶号
112. 2）用于item lock表中锁住item，通过hv计算出应该用item lock表中哪个锁对当前item进行加锁
113. 这两者都涉及到一个粒度问题，不可能保证每个不一样的key的hv不会相同，所有hash方法都可能
114. 出现冲突。
115. 所以hash表中用链表的方式处理冲突的item，而item lock表中会多个item共享一个锁，或者说
116. 多个桶共享一个锁。
117. */
118. uint32_t hv = hash(ITEM_key(search), search->nkey);
119. /**
120. 尝试去锁住当前item。
121. */
122. if (hv == cur_hv || (hold_lock = item_trylock(hv)) == NULL)
123. continue;
124. /* Now see if the item is refcount locked */
125. if (refcount_incr(&search->refcount) != 2) {
126. refcount_decr(&search->refcount);
127. /* Old rare bug could cause a refcount leak. We haven't seen
128. * it in years, but we leave this code in to prevent failures
129. * just in case
130. 没看懂这里的意思.....
131. */
132. if (settings.tail_repair_time &&
133. search->time + settings.tail_repair_time < current_time) {
134. itemstats[id].tailrepairs++;
135. search->refcount = 1;
136. do_item_unlink_nolock(search, hv);
137. }
138. if (hold_lock)
139. item_trylock_unlock(hold_lock);
140. continue;
141. }
142. /* Expired or flushed */
143. //超时了...
144. if ((search->exptime != 0 && search->exptime < current_time)
145. || (search->time <= oldest_live && oldest_live <= current_time)) {
146. itemstats[id].reclaimed++;
147. if ((search->it_flags & ITEM_FETCHED) == 0) {
148. itemstats[id].expired_unfetched++;
149. }
150. it = search; //拿下空间
151. slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal); //更新统计数据
152. /**
153. 什么是link，在这简单说下，就是把item加到哈希表和LRU链表的过程。详见items::do_item_link函数这里把item旧的link取消掉，当前函数do_item_alloc的工作只是拿空间，而往后可知道拿到item空间后会对这块item进行“link”工作，而这里这块item空间是旧的item超时然后拿来用的，所以先把它unlink掉
154. */
155. do_item_unlink_nolock(it, hv);
156. /* Initialize the item block: */
157. it->slabs_clsid = 0;
158. } else if ((it = slabs_alloc(ntotal, id)) == NULL) {/*如果没有找到超时的item，则
159. 调用slabs_alloc分配空间，详见slabs_alloc
160. 如果slabs_alloc分配空间失败，即返回NULL，则往下走，下面的代码是
161. 把LRU列表最后一个给淘汰，即使item没有过期。
162. 这里一般是可用内存已经满了，需要按LRU进行淘汰的时候。
163. //************mark: $1**************
164. */
165. tried_alloc = 1; //标记一下，表示有进入此分支，表示有尝试过调用slabs_alloc去分配新的空间。
166. //记下被淘汰item的信息，像我们使用memcached经常会查看的evicted_time就是在这里赋值啦！
167. if (settings.evict_to_free == 0) {
168. itemstats[id].outofmemory++;
169. } else {
170. itemstats[id].evicted++;
171. itemstats[id].evicted_time = current_time - search->time; //被淘汰的item距离上次使用多长时间了
172. if (search->exptime != 0)
173. itemstats[id].evicted_nonzero++;
174. if ((search->it_flags & ITEM_FETCHED) == 0) {
175. itemstats[id].evicted_unfetched++;
176. }
177. it = search;
178. slabs_adjust_mem_requested(it->slabs_clsid, ITEM_ntotal(it), ntotal);//更新统计数据
179. do_item_unlink_nolock(it, hv); //从哈希表和LRU链表中删掉
180. /* Initialize the item block: */
181. it->slabs_clsid = 0;
182. /*
183. 如果当前slabclass有item被淘汰掉了，说明可用内存都满了，再也没有
184. slab可分配了，
185. 而如果 slab_automove=2 (默认是1)，这样会导致angry模式，
186. 就是只要分配失败了，就马上进行slab重分配：把别的slabclass空间牺牲
187. 掉一些，马上给现在的slabclass分配空间，而不会合理地根据淘汰统计
188. 数据来分析要怎么重分配（slab_automove = 1则会）。
189. */
190. if (settings.slab_automove == 2)
191. slabs_reassign(-1, id);
192. }
193. }
194. refcount_decr(&search->refcount);
195. /* If hash values were equal, we don't grab a second lock */
196. if (hold_lock)
197. item_trylock_unlock(hold_lock);
198. break;
199. }
200. /**
201. 如果上面的for循环里面没有找到空间，并且没有进入过else if ((it = slabs_alloc(ntotal, id)) == NULL)这个分支没有
202. 尝试调slabs_alloc分配空间（有这种可能性），那么，下面这行代码就是再尝试分配。
203. 你会觉得上面那个循环写得特纠结，逻辑不清，估计你也看醉了。其实整个分配原则是这样子：
204. 1）先从LRU链表找下看看有没有恰好过期的空间，有的话就用这个空间。
205. 2）如果没有过期的空间，就分配新的空间。
206. 3）如果分配新的空间失败，那么往往是内存都用光了，则从LRU链表中把最旧的即使没过期的item淘汰掉，空间分给新的item用。
207. 问题是：这个从“LRU链表找到的item”是一个不确定的东西，有可能这个item数据异常，有可能这个item由于与别的item共用锁的桶号
208. 这个桶被锁住了，所以总之各种原因这个item此刻不一定可用，因此用了一个循环尝试找几次（上面是5）。
209. 所以逻辑是：
210. 1）我先找5次LRU看看有没有可用的过期的item，有就用它。（for循环5次）
211. 2）5次没有找到可用的过期的item，那我分配新的。
212. 3）分配新的不成功，那我再找5次看看有没有可用的虽然没过期的item，淘汰它，把空间给新的item用。（for循环5次）
213. 那么这里有个问题，如果代码要写得逻辑清晰一点，我得写两个for循环，一个是为了第2）步前“找可用的过期的”item，
214. 一个是第2）步不成功后“找可用的用来淘汰的”空间。而且有重复的逻辑“找到可用的”，所以memcached作者就合在一起了，
215. 然后只能把第2）步也塞到for循环里面，确实挺尴尬的。。。估计memcached作者也写得很纠结。。。
216. 所以就很有可能出现5次都没找到可用的空间，都没进入过elseif那个分支就被continue掉了，为了记下有没有进过elseif
217. 分支就挫挫地用一个tried_alloc变量来做记号。。
218. */
219. if (!tried_alloc && (tries == 0 || search == NULL))
220. it = slabs_alloc(ntotal, id);
221. if (it == NULL) {
222. itemstats[id].outofmemory++;
223. mutex_unlock(&cache_lock);
224. return NULL; //没错！会有分配新空间不成功，而且尝试5次淘汰旧的item也没成功的时候，只能返回NULL。。
225. }
226. assert(it->slabs_clsid == 0);
227. assert(it != heads[id]);
228. //来到这里，说明item分配成功，下面主要是一些初始化工作。
229. /* Item initialization can happen outside of the lock; the item's already
230. * been removed from the slab LRU.
231. */
232. it->refcount = 1; /* the caller will have a reference */
233. mutex_unlock(&cache_lock);
234. it->next = it->prev = it->h_next = 0;
235. it->slabs_clsid = id;
236. DEBUG_REFCNT(it, '*');
237. it->it_flags = settings.use_cas ? ITEM_CAS : 0;
238. it->nkey = nkey;
239. it->nbytes = nbytes;
240. memcpy(ITEM_key(it), key, nkey);
241. it->exptime = exptime;
242. memcpy(ITEM_suffix(it), suffix, (size_t)nsuffix);
243. it->nsuffix = nsuffix;
244. return it;
245. }
246. /**
247. 把这块item free掉，以供再利用，注意这里的free不是指把内存空间释放哦，
248. 而是把这块item 变为“空闲”
249. */
250. void item_free(item *it) {
251. size_t ntotal = ITEM_ntotal(it);
252. unsigned int clsid;
253. assert((it->it_flags & ITEM_LINKED) == 0);
254. assert(it != heads[it->slabs_clsid]);
255. assert(it != tails[it->slabs_clsid]);
256. assert(it->refcount == 0);
257. /* so slab size changer can tell later if item is already free or not */
258. clsid = it->slabs_clsid;
259. it->slabs_clsid = 0; //在这把free掉的item 的slabs_clsid设为0
260. DEBUG_REFCNT(it, 'F');
261. slabs_free(it, ntotal, clsid);
262. }
263. /**
264. * 检查item大小
265. */
266. bool item_size_ok(const size_t nkey, const int flags, const int nbytes) {
267. char prefix[40];
268. uint8_t nsuffix;
269. size_t ntotal = item_make_header(nkey + 1, flags, nbytes,
270. prefix, &nsuffix);
271. if (settings.use_cas) {
272. ntotal += sizeof(uint64_t);
273. }
274. return slabs_clsid(ntotal) != 0;
275. }
276. /**
277. 把item插入相应的slabclass lru链表中而已
278. */
279. static void item_link_q(item *it) { /* item is the new head */
280. item **head, **tail;
281. assert(it->slabs_clsid < LARGEST_ID);
282. assert((it->it_flags & ITEM_SLABBED) == 0);
283. head = &heads[it->slabs_clsid];
284. tail = &tails[it->slabs_clsid];
285. assert(it != *head);
286. assert((*head && *tail) || (*head == 0 && *tail == 0));
287. it->prev = 0;
288. it->next = *head;
289. if (it->next) it->next->prev = it;
290. *head = it;
291. if (*tail == 0) *tail = it;
292. sizes[it->slabs_clsid]++;
293. return;
294. }
295. /**
296. 把item从相应的slabclass lru链表中删掉而已，下面就是经典的删除链表逻辑代码了
297. */
298. static void item_unlink_q(item *it) {
299. item **head, **tail;
300. assert(it->slabs_clsid < LARGEST_ID);
301. head = &heads[it->slabs_clsid];
302. tail = &tails[it->slabs_clsid];
303. if (*head == it) {
304. assert(it->prev == 0);
305. *head = it->next;
306. }
307. if (*tail == it) {
308. assert(it->next == 0);
309. *tail = it->prev;
310. }
311. assert(it->next != it);
312. assert(it->prev != it);
313. if (it->next) it->next->prev = it->prev;
314. if (it->prev) it->prev->next = it->next;
315. sizes[it->slabs_clsid]--;
316. return;
317. }
318. /**
319. 把item "link"起来，主要包括：
320. 1）改变一些统计数据
321. 2）把item加到哈希表
322. 3）把item插入到相应的slabclass lru链表中
323. */
324. int do_item_link(item *it, const uint32_t hv) {
325. MEMCACHED_ITEM_LINK(ITEM_key(it), it->nkey, it->nbytes);
326. assert((it->it_flags & (ITEM_LINKED|ITEM_SLABBED)) == 0);
327. mutex_lock(&cache_lock);
328. it->it_flags |= ITEM_LINKED;
329. it->time = current_time;
330. STATS_LOCK();
331. stats.curr_bytes += ITEM_ntotal(it);
332. stats.curr_items += 1;
333. stats.total_items += 1;
334. STATS_UNLOCK();
335. /* Allocate a new CAS ID on link. */
336. ITEM_set_cas(it, (settings.use_cas) ? get_cas_id() : 0);
337. assoc_insert(it, hv); //插入哈希表
338. item_link_q(it); //加入LRU链表
339. refcount_incr(&it->refcount);
340. mutex_unlock(&cache_lock);
341. return 1;
342. }
343. /**
344. 就是和do_item_link反过来的一些操作
345. */
346. void do_item_unlink(item *it, const uint32_t hv) {
347. MEMCACHED_ITEM_UNLINK(ITEM_key(it), it->nkey, it->nbytes);
348. mutex_lock(&cache_lock);
349. if ((it->it_flags & ITEM_LINKED) != 0) {
350. it->it_flags &= ~ITEM_LINKED;
351. STATS_LOCK();
352. stats.curr_bytes -= ITEM_ntotal(it);
353. stats.curr_items -= 1;
354. STATS_UNLOCK();
355. assoc_delete(ITEM_key(it), it->nkey, hv);
356. item_unlink_q(it);
357. do_item_remove(it);
358. }
359. mutex_unlock(&cache_lock);
360. }
361. /* FIXME: Is it necessary to keep this copy/pasted code? */
362. void do_item_unlink_nolock(item *it, const uint32_t hv) {
363. MEMCACHED_ITEM_UNLINK(ITEM_key(it), it->nkey, it->nbytes);
364. if ((it->it_flags & ITEM_LINKED) != 0) {
365. it->it_flags &= ~ITEM_LINKED;
366. STATS_LOCK();
367. stats.curr_bytes -= ITEM_ntotal(it);
368. stats.curr_items -= 1;
369. STATS_UNLOCK();
370. assoc_delete(ITEM_key(it), it->nkey, hv);
371. item_unlink_q(it);
372. do_item_remove(it);
373. }
374. }
375. /**
376. 指向item的指针不用的时候都会调用此函数
377. */
378. void do_item_remove(item *it) {
379. MEMCACHED_ITEM_REMOVE(ITEM_key(it), it->nkey, it->nbytes);
380. assert((it->it_flags & ITEM_SLABBED) == 0);
381. assert(it->refcount > 0);
382. if (refcount_decr(&it->refcount) == 0) { //引用计数减1，当引用计数为0时，才真正把item free掉。
383. item_free(it);
384. }
385. }
386. /**
387. 主要作用是重置在最近使用链表中的位置，更新最近使用时间
388. */
389. void do_item_update(item *it) {
390. MEMCACHED_ITEM_UPDATE(ITEM_key(it), it->nkey, it->nbytes);
391. if (it->time < current_time - ITEM_UPDATE_INTERVAL) {
392. assert((it->it_flags & ITEM_SLABBED) == 0);
393. mutex_lock(&cache_lock);
394. if ((it->it_flags & ITEM_LINKED) != 0) {
395. item_unlink_q(it);
396. it->time = current_time;
397. item_link_q(it);
398. }
399. mutex_unlock(&cache_lock);
400. }
401. }
402. int do_item_replace(item *it, item *new_it, const uint32_t hv) {
403. MEMCACHED_ITEM_REPLACE(ITEM_key(it), it->nkey, it->nbytes,
404. ITEM_key(new_it), new_it->nkey, new_it->nbytes);
405. assert((it->it_flags & ITEM_SLABBED) == 0);
406. do_item_unlink(it, hv);
407. return do_item_link(new_it, hv);
408. }
409. void item_stats_evictions(uint64_t *evicted) {
410. int i;
411. mutex_lock(&cache_lock);
412. for (i = 0; i < LARGEST_ID; i++) {
413. evicted[i] = itemstats[i].evicted;
414. }
415. mutex_unlock(&cache_lock);
416. }
417. void do_item_stats_totals(ADD_STAT add_stats, void *c) {
418. itemstats_t totals;
419. memset(&totals, 0, sizeof(itemstats_t));
420. int i;
421. for (i = 0; i < LARGEST_ID; i++) {
422. totals.expired_unfetched += itemstats[i].expired_unfetched;
423. totals.evicted_unfetched += itemstats[i].evicted_unfetched;
424. totals.evicted += itemstats[i].evicted;
425. totals.reclaimed += itemstats[i].reclaimed;
426. totals.crawler_reclaimed += itemstats[i].crawler_reclaimed;
427. }
428. APPEND_STAT("expired_unfetched", "%llu",
429. (unsigned long long)totals.expired_unfetched);
430. APPEND_STAT("evicted_unfetched", "%llu",
431. (unsigned long long)totals.evicted_unfetched);
432. APPEND_STAT("evictions", "%llu",
433. (unsigned long long)totals.evicted);
434. APPEND_STAT("reclaimed", "%llu",
435. (unsigned long long)totals.reclaimed);
436. APPEND_STAT("crawler_reclaimed", "%llu",
437. (unsigned long long)totals.crawler_reclaimed);
438. }
439. void do_item_stats(ADD_STAT add_stats, void *c) {
440. int i;
441. for (i = 0; i < LARGEST_ID; i++) {
442. if (tails[i] != NULL) {
443. const char *fmt = "items:%d:%s";
444. char key_str[STAT_KEY_LEN];
445. char val_str[STAT_VAL_LEN];
446. int klen = 0, vlen = 0;
447. if (tails[i] == NULL) {
448. /* We removed all of the items in this slab class */
449. continue;
450. }
451. APPEND_NUM_FMT_STAT(fmt, i, "number", "%u", sizes[i]);
452. APPEND_NUM_FMT_STAT(fmt, i, "age", "%u", current_time - tails[i]->time);
453. APPEND_NUM_FMT_STAT(fmt, i, "evicted",
454. "%llu", (unsigned long long)itemstats[i].evicted);
455. APPEND_NUM_FMT_STAT(fmt, i, "evicted_nonzero",
456. "%llu", (unsigned long long)itemstats[i].evicted_nonzero);
457. APPEND_NUM_FMT_STAT(fmt, i, "evicted_time",
458. "%u", itemstats[i].evicted_time);
459. APPEND_NUM_FMT_STAT(fmt, i, "outofmemory",
460. "%llu", (unsigned long long)itemstats[i].outofmemory);
461. APPEND_NUM_FMT_STAT(fmt, i, "tailrepairs",
462. "%llu", (unsigned long long)itemstats[i].tailrepairs);
463. APPEND_NUM_FMT_STAT(fmt, i, "reclaimed",
464. "%llu", (unsigned long long)itemstats[i].reclaimed);
465. APPEND_NUM_FMT_STAT(fmt, i, "expired_unfetched",
466. "%llu", (unsigned long long)itemstats[i].expired_unfetched);
467. APPEND_NUM_FMT_STAT(fmt, i, "evicted_unfetched",
468. "%llu", (unsigned long long)itemstats[i].evicted_unfetched);
469. APPEND_NUM_FMT_STAT(fmt, i, "crawler_reclaimed",
470. "%llu", (unsigned long long)itemstats[i].crawler_reclaimed);
471. }
472. }
473. /* getting here means both ascii and binary terminators fit */
474. add_stats(NULL, 0, NULL, 0, c);
475. }
476. void do_item_stats_sizes(ADD_STAT add_stats, void *c) {
477. /* max 1MB object, divided into 32 bytes size buckets */
478. const int num_buckets = 32768;
479. unsigned int *histogram = calloc(num_buckets, sizeof(int));
480. if (histogram != NULL) {
481. int i;
482. /* build the histogram */
483. for (i = 0; i < LARGEST_ID; i++) {
484. item *iter = heads[i];
485. while (iter) {
486. int ntotal = ITEM_ntotal(iter);
487. int bucket = ntotal / 32;
488. if ((ntotal % 32) != 0) bucket++;
489. if (bucket < num_buckets) histogram[bucket]++;
490. iter = iter->next;
491. }
492. }
493. /* write the buffer */
494. for (i = 0; i < num_buckets; i++) {
495. if (histogram[i] != 0) {
496. char key[8];
497. snprintf(key, sizeof(key), "%d", i * 32);
498. APPEND_STAT(key, "%u", histogram[i]);
499. }
500. }
501. free(histogram);
502. }
503. add_stats(NULL, 0, NULL, 0, c);
504. }
505. //读取item数据
506. item *do_item_get(const char *key, const size_t nkey, const uint32_t hv) {
507. //mutex_lock(&cache_lock);
508. item *it = assoc_find(key, nkey, hv);
509. if (it != NULL) {
510. refcount_incr(&it->refcount);
511. if (slab_rebalance_signal &&
512. ((void *)it >= slab_rebal.slab_start && (void *)it < slab_rebal.slab_end)) {
513. do_item_unlink_nolock(it, hv);
514. do_item_remove(it);
515. it = NULL;
516. }
517. }
518. //mutex_unlock(&cache_lock);
519. int was_found = 0;
520. if (settings.verbose > 2) {
521. int ii;
522. if (it == NULL) {
523. fprintf(stderr, "> NOT FOUND ");
524. } else {
525. fprintf(stderr, "> FOUND KEY ");
526. was_found++;
527. }
528. for (ii = 0; ii < nkey; ++ii) {
529. fprintf(stderr, "%c", key[ii]);
530. }
531. }
532. if (it != NULL) {
533. if (settings.oldest_live != 0 && settings.oldest_live <= current_time &&
534. it->time <= settings.oldest_live) {
535. do_item_unlink(it, hv);
536. do_item_remove(it);
537. it = NULL;
538. if (was_found) {
539. fprintf(stderr, " -nuked by flush");
540. }
541. } else if (it->exptime != 0 && it->exptime <= current_time) {
542. do_item_unlink(it, hv);
543. do_item_remove(it);
544. it = NULL;
545. if (was_found) {
546. fprintf(stderr, " -nuked by expire");
547. }
548. } else {
549. it->it_flags |= ITEM_FETCHED;
550. DEBUG_REFCNT(it, '+');
551. }
552. }
553. if (settings.verbose > 2)
554. fprintf(stderr, "\n");
555. return it;
556. }
557. item *do_item_touch(const char *key, size_t nkey, uint32_t exptime,
558. const uint32_t hv) {
559. item *it = do_item_get(key, nkey, hv);
560. if (it != NULL) {
561. it->exptime = exptime;
562. }
563. return it;
564. }
565. /* expires items that are more recent than the oldest_live setting. */
566. void do_item_flush_expired(void) {
567. int i;
568. item *iter, *next;
569. if (settings.oldest_live == 0)
570. return;
571. for (i = 0; i < LARGEST_ID; i++) {
572. for (iter = heads[i]; iter != NULL; iter = next) {
573. /* iter->time of 0 are magic objects. */
574. if (iter->time != 0 && iter->time >= settings.oldest_live) {
575. next = iter->next;
576. if ((iter->it_flags & ITEM_SLABBED) == 0) {
577. do_item_unlink_nolock(iter, hash(ITEM_key(iter), iter->nkey));
578. }
579. } else {
580. /* We've hit the first old item. Continue to the next queue. */
581. break;
582. }
583. }
584. }
585. }
586. static void crawler_link_q(item *it) { /* item is the new tail */
587. item **head, **tail;
588. assert(it->slabs_clsid < LARGEST_ID);
589. assert(it->it_flags == 1);
590. assert(it->nbytes == 0);
591. head = &heads[it->slabs_clsid];
592. tail = &tails[it->slabs_clsid];
593. assert(*tail != 0);
594. assert(it != *tail);
595. assert((*head && *tail) || (*head == 0 && *tail == 0));
596. it->prev = *tail;
597. it->next = 0;
598. if (it->prev) {
599. assert(it->prev->next == 0);
600. it->prev->next = it;
601. }
602. *tail = it;
603. if (*head == 0) *head = it;
604. return;
605. }
606. static void crawler_unlink_q(item *it) {
607. item **head, **tail;
608. assert(it->slabs_clsid < LARGEST_ID);
609. head = &heads[it->slabs_clsid];
610. tail = &tails[it->slabs_clsid];
611. if (*head == it) {
612. assert(it->prev == 0);
613. *head = it->next;
614. }
615. if (*tail == it) {
616. assert(it->next == 0);
617. *tail = it->prev;
618. }
619. assert(it->next != it);
620. assert(it->prev != it);
621. if (it->next) it->next->prev = it->prev;
622. if (it->prev) it->prev->next = it->next;
623. return;
624. }
625. static item *crawler_crawl_q(item *it) {
626. item **head, **tail;
627. assert(it->it_flags == 1);
628. assert(it->nbytes == 0);
629. assert(it->slabs_clsid < LARGEST_ID);
630. head = &heads[it->slabs_clsid];
631. tail = &tails[it->slabs_clsid];
632. /* We've hit the head, pop off */
633. if (it->prev == 0) {
634. assert(*head == it);
635. if (it->next) {
636. *head = it->next;
637. assert(it->next->prev == it);
638. it->next->prev = 0;
639. }
640. return NULL; /* Done */
641. }
642. assert(it->prev != it);
643. if (it->prev) {
644. if (*head == it->prev) {
645. *head = it;
646. }
647. if (*tail == it) {
648. *tail = it->prev;
649. }
650. assert(it->next != it);
651. if (it->next) {
652. assert(it->prev->next == it);
653. it->prev->next = it->next;
654. it->next->prev = it->prev;
655. } else {
656. it->prev->next = 0;
657. }
658. it->next = it->prev;
659. it->prev = it->next->prev;
660. it->next->prev = it;
661. if (it->prev) {
662. it->prev->next = it;
663. }
664. }
665. assert(it->next != it);
666. assert(it->prev != it);
667. return it->next; /* success */
668. }
669. /* I pulled this out to make the main thread clearer, but it reaches into the
670. * main thread's values too much. Should rethink again.
671. 上面这句注释作者是说，他把用爬虫处理过期的item的工作放到另一个专门的线程里去做
672. 是为了让主线程干净一点，但是这线程的工作涉及到太多主线程的东西了，得重新想想..
673. 这个函数的作用是“评估”一下这个item是否应该free掉。其实主要就是看下有没有过期啦~
674. 当然用户设置的settings.oldest_live参数也加入到考虑中
675. */
676. static void item_crawler_evaluate(item *search, uint32_t hv, int i) {
677. rel_time_t oldest_live = settings.oldest_live;
678. if ((search->exptime != 0 && search->exptime < current_time)
679. || (search->time <= oldest_live && oldest_live <= current_time)) {
680. itemstats[i].crawler_reclaimed++;
681. if (settings.verbose > 1) {
682. int ii;
683. char *key = ITEM_key(search);
684. fprintf(stderr, "LRU crawler found an expired item (flags: %d, slab: %d): ",
685. search->it_flags, search->slabs_clsid);
686. for (ii = 0; ii < search->nkey; ++ii) {
687. fprintf(stderr, "%c", key[ii]);
688. }
689. fprintf(stderr, "\n");
690. }
691. if ((search->it_flags & ITEM_FETCHED) == 0) {
692. itemstats[i].expired_unfetched++;
693. }
694. do_item_unlink_nolock(search, hv);
695. do_item_remove(search);
696. assert(search->slabs_clsid == 0);
697. } else {
698. refcount_decr(&search->refcount);
699. }
700. }
701. /**
702. item爬虫线程入口，负责从lru链表中把过期的item free掉
703. */
704. static void *item_crawler_thread(void *arg) {
705. int i;
706. pthread_mutex_lock(&lru_crawler_lock);
707. if (settings.verbose > 2)
708. fprintf(stderr, "Starting LRU crawler background thread\n");
709. while (do_run_lru_crawler_thread) {
710. pthread_cond_wait(&lru_crawler_cond, &lru_crawler_lock);
711. while (crawler_count) {
712. item *search = NULL;
713. void *hold_lock = NULL;
714. for (i = 0; i < LARGEST_ID; i++) {
715. if (crawlers[i].it_flags != 1) {
716. continue;
717. }
718. pthread_mutex_lock(&cache_lock);
719. search = crawler_crawl_q((item *)&crawlers[i]);
720. if (search == NULL ||
721. (crawlers[i].remaining && --crawlers[i].remaining < 1)) {
722. if (settings.verbose > 2)
723. fprintf(stderr, "Nothing left to crawl for %d\n", i);
724. crawlers[i].it_flags = 0;
725. crawler_count--;
726. crawler_unlink_q((item *)&crawlers[i]);
727. pthread_mutex_unlock(&cache_lock);
728. continue;
729. }
730. uint32_t hv = hash(ITEM_key(search), search->nkey);
731. /* Attempt to hash item lock the "search" item. If locked, no
732. * other callers can incr the refcount
733. */
734. if ((hold_lock = item_trylock(hv)) == NULL) {
735. pthread_mutex_unlock(&cache_lock);
736. continue;
737. }
738. /* Now see if the item is refcount locked */
739. if (refcount_incr(&search->refcount) != 2) {
740. refcount_decr(&search->refcount);
741. if (hold_lock)
742. item_trylock_unlock(hold_lock);
743. pthread_mutex_unlock(&cache_lock);
744. continue;
745. }
746. item_crawler_evaluate(search, hv, i);
747. if (hold_lock)
748. item_trylock_unlock(hold_lock);
749. pthread_mutex_unlock(&cache_lock);
750. if (settings.lru_crawler_sleep)
751. usleep(settings.lru_crawler_sleep);
752. }
753. }
754. if (settings.verbose > 2)
755. fprintf(stderr, "LRU crawler thread sleeping\n");
756. STATS_LOCK();
757. stats.lru_crawler_running = false;
758. STATS_UNLOCK();
759. }
760. pthread_mutex_unlock(&lru_crawler_lock);
761. if (settings.verbose > 2)
762. fprintf(stderr, "LRU crawler thread stopping\n");
763. return NULL;
764. }
765. static pthread_t item_crawler_tid;
766. //停止item爬虫线程
767. int stop_item_crawler_thread(void) {
768. int ret;
769. pthread_mutex_lock(&lru_crawler_lock);
770. do_run_lru_crawler_thread = 0;
771. pthread_cond_signal(&lru_crawler_cond);
772. pthread_mutex_unlock(&lru_crawler_lock);
773. if ((ret = pthread_join(item_crawler_tid, NULL)) != 0) {
774. fprintf(stderr, "Failed to stop LRU crawler thread: %s\n", strerror(ret));
775. return -1;
776. }
777. settings.lru_crawler = false;
778. return 0;
779. }
780. /**
781. 启动item 爬虫线程
782. */
783. int start_item_crawler_thread(void) {
784. int ret;
785. if (settings.lru_crawler)
786. return -1;
787. pthread_mutex_lock(&lru_crawler_lock);
788. do_run_lru_crawler_thread = 1;
789. settings.lru_crawler = true;
790. if ((ret = pthread_create(&item_crawler_tid, NULL,
791. item_crawler_thread, NULL)) != 0) {
792. fprintf(stderr, "Can't create LRU crawler thread: %s\n",
793. strerror(ret));
794. pthread_mutex_unlock(&lru_crawler_lock);
795. return -1;
796. }
797. pthread_mutex_unlock(&lru_crawler_lock);
798. return 0;
799. }
800. enum crawler_result_type lru_crawler_crawl(char *slabs) {
801. char *b = NULL;
802. uint32_t sid = 0;
803. uint8_t tocrawl[POWER_LARGEST];
804. if (pthread_mutex_trylock(&lru_crawler_lock) != 0) {
805. return CRAWLER_RUNNING;
806. }
807. pthread_mutex_lock(&cache_lock);
808. if (strcmp(slabs, "all") == 0) {
809. for (sid = 0; sid < LARGEST_ID; sid++) {
810. tocrawl[sid] = 1;
811. }
812. } else {
813. for (char *p = strtok_r(slabs, ",", &b);
814. p != NULL;
815. p = strtok_r(NULL, ",", &b)) {
816. if (!safe_strtoul(p, &sid) || sid < POWER_SMALLEST
817. || sid > POWER_LARGEST) {
818. pthread_mutex_unlock(&cache_lock);
819. pthread_mutex_unlock(&lru_crawler_lock);
820. return CRAWLER_BADCLASS;
821. }
822. tocrawl[sid] = 1;
823. }
824. }
825. for (sid = 0; sid < LARGEST_ID; sid++) {
826. if (tocrawl[sid] != 0 && tails[sid] != NULL) {
827. if (settings.verbose > 2)
828. fprintf(stderr, "Kicking LRU crawler off for slab %d\n", sid);
829. crawlers[sid].nbytes = 0;
830. crawlers[sid].nkey = 0;
831. crawlers[sid].it_flags = 1; /* For a crawler, this means enabled. */
832. crawlers[sid].next = 0;
833. crawlers[sid].prev = 0;
834. crawlers[sid].time = 0;
835. crawlers[sid].remaining = settings.lru_crawler_tocrawl;
836. crawlers[sid].slabs_clsid = sid;
837. crawler_link_q((item *)&crawlers[sid]);
838. crawler_count++;
839. }
840. }
841. pthread_mutex_unlock(&cache_lock);
842. pthread_cond_signal(&lru_crawler_cond);
843. STATS_LOCK();
844. stats.lru_crawler_running = true;
845. STATS_UNLOCK();
846. pthread_mutex_unlock(&lru_crawler_lock);
847. return CRAWLER_OK;
848. }
849. //初始化lru item爬虫线程
850. int init_lru_crawler(void) {
851. if (lru_crawler_initialized == 0) {
852. if (pthread_cond_init(&lru_crawler_cond, NULL) != 0) {
853. fprintf(stderr, "Can't initialize lru crawler condition\n");
854. return -1;
855. }
856. pthread_mutex_init(&lru_crawler_lock, NULL);
857. lru_crawler_initialized = 1;
858. }
859. return 0;
860. }