107 lines
4.1 KiB
C
107 lines
4.1 KiB
C
/*
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* stat cache - speeding up stat()s
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*
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* The basic idea behind the stat cache is to reduce calls to stat() which might block due to disk io (some ms).
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* Each worker thread has its own cache so no locking contention between threads happens which could be slow.
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* This means that there will be more blocking stat() calls than there would be with only one shared cache but since there
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* should be mostly hits in most cases (few items requested frequently) it will outweight the locking contention.
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* To prevent the stat() from blocking all other requests of that worker, we hand it over to another thread.
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*
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* Entries are removed after 10 seconds (adjustable through stat_cache.ttl setup)
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*
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* TODO:
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* - create ETAGs
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* - get content type from xattr
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* - add support for inotify (linux). TTL for entries can be increased to 60s
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*
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* Technical details:
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* If a stat is requested, the following procedure takes place:
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* - a cache lookup is performed
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* - in case of a cache HIT:
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* - if state is FINISHED and entry is fresh then return HANDLER_GO_ON
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* - if state is WAITING then add vrequest to entry and return HANDLER_WAIT_FOR_EVENT (looks like a cache miss)
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* - in case of a cache MISS:
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* - a new entry is allocated and inserted into the cache, state is set to WAITING
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* - the entry is inserted into the delete queue
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* - a new job is created and HANDLER_WAIT_FOR_EVENT returned
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* - in case of an ERROR:
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* - return HANDLER_ERROR
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*
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* In the delete queue callback we check if no vrequests are working on that entry. If yes, we free it. If not then we requeue it.
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* Locking only happens in two cases: 1) a new job is send to the stat thread 2) the stat thread sends the info back to the worker.
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*
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*/
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#ifndef _LIGHTTPD_STAT_CACHE_H_
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#define _LIGHTTPD_STAT_CACHE_H_
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#ifndef _LIGHTTPD_BASE_H_
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#error Please include <lighttpd/base.h> instead of this file
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#endif
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struct liStatCacheEntryData {
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GString *path;
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GString *etag;
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GString *content_type;
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gboolean failed;
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struct stat st;
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gint err;
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};
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struct liStatCacheEntry {
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enum {
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STAT_CACHE_ENTRY_SINGLE, /* single file, this is the default or "normal" */
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STAT_CACHE_ENTRY_DIR /* get a directory listing (with stat info) */
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} type;
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enum {
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STAT_CACHE_ENTRY_WAITING, /* waiting for stat thread to do the work, no info available */
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STAT_CACHE_ENTRY_FINISHED, /* stat() done, info available */
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} state;
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liStatCacheEntryData data;
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GArray *dirlist; /* array of stat_cache_entry_data, used together with STAT_CACHE_ENTRY_DIR */
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GPtrArray *vrequests; /* vrequests waiting for this info */
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guint refcount;
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liWaitQueueElem queue_elem; /* queue element for the delete_queue */
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gboolean cached;
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};
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struct liStatCache {
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GHashTable *dirlists;
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GHashTable *entries;
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GAsyncQueue *job_queue_out; /* elements waiting for stat */
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GAsyncQueue *job_queue_in; /* elements with finished stat */
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liWaitQueue delete_queue;
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GThread *thread;
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ev_async job_watcher;
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gdouble ttl;
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guint64 hits;
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guint64 misses;
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guint64 errors;
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};
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LI_API void li_stat_cache_new(liWorker *wrk, gdouble ttl);
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LI_API void li_stat_cache_free(liStatCache *sc);
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/*
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gets a stat_cache_entry for a specified path
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if fd is set, a new fd is acquired via open() and stat info via fstat(), otherwise only a stat() is performed
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returns HANDLER_WAIT_FOR_EVENT in case of a cache MISS, HANDLER_GO_ON in case of a hit and HANDLER_ERROR in case of an error
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*/
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LI_API liHandlerResult li_stat_cache_get(liVRequest *vr, GString *path, struct stat *st, int *err, int *fd);
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/*
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sce->dirlist will contain a list of stat_cache_entry_data upon success
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returns HANDLER_WAIT_FOR_EVENT in case of a cache MISS, HANDLER_GO_ON in case of a hit and HANDLER_ERROR in case of an error
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*/
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LI_API liHandlerResult li_stat_cache_get_dirlist(liVRequest *vr, GString *path, liStatCacheEntry **result);
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LI_API void li_stat_cache_entry_acquire(liVRequest *vr, liStatCacheEntry *sce);
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/* release a stat_cache_entry so it can be cleaned up */
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LI_API void li_stat_cache_entry_release(liVRequest *vr, liStatCacheEntry *sce);
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#endif
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