mod_mem_cache.c

Apache HTTP Server 是一个功能强大的灵活的与HTTP/1.1相兼容的web服务器.这里给出的是Apache HTTP服务器的源码。

/* Copyright 2001-2005 The Apache Software Foundation or its licensors, as
 * applicable.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * Rules for managing obj->refcount:
 * refcount should be incremented when an object is placed in the cache. Insertion 
 *   of an object into the cache and the refcount increment should happen under 
 *   protection of the sconf->lock.
 *
 * refcount should be decremented when the object is removed from the cache.
 *   Object should be removed from the cache and the refcount decremented while
 *   under protection of the sconf->lock.
 * 
 * refcount should be incremented when an object is retrieved from the cache
 *   by a worker thread. The retrieval/find operation and refcount increment
 *   should occur under protection of the sconf->lock
 *
 * refcount can be atomically decremented w/o protection of the sconf->lock
 *   by worker threads.
 *
 * Any object whose refcount drops to 0 should be freed/cleaned up. A refcount 
 * of 0 means the object is not in the cache and no worker threads are accessing 
 * it.
 */
#define CORE_PRIVATE
#include "mod_cache.h"
#include "cache_pqueue.h"
#include "cache_cache.h"
#include "ap_provider.h"
#include "ap_mpm.h"
#include "apr_thread_mutex.h"
#if APR_HAVE_UNISTD_H
#include <unistd.h>
#endif

#if !APR_HAS_THREADS
#error This module does not currently compile unless you have a thread-capable APR. Sorry!
#endif

module AP_MODULE_DECLARE_DATA mem_cache_module;

typedef enum {
    CACHE_TYPE_FILE = 1,
    CACHE_TYPE_HEAP,
    CACHE_TYPE_MMAP
} cache_type_e;

typedef struct {
    char* hdr;
    char* val;
} cache_header_tbl_t;

typedef struct mem_cache_object {
    cache_type_e type;
    apr_ssize_t num_header_out;
    apr_ssize_t num_err_header_out;
    apr_ssize_t num_subprocess_env;
    apr_ssize_t num_notes;
    apr_ssize_t num_req_hdrs;
    cache_header_tbl_t *header_out;
    cache_header_tbl_t *err_header_out;
    cache_header_tbl_t *subprocess_env;
    cache_header_tbl_t *notes;
    cache_header_tbl_t *req_hdrs; /* for Vary negotiation */
    apr_size_t m_len;
    void *m;
    apr_os_file_t fd;
    apr_int32_t flags;  /* File open flags */
    long priority;      /**< the priority of this entry */
    long total_refs;          /**< total number of references this entry has had */

    apr_uint32_t pos;   /**< the position of this entry in the cache */

} mem_cache_object_t;

typedef struct {
    apr_thread_mutex_t *lock;
    cache_cache_t *cache_cache;

    /* Fields set by config directives */
    apr_size_t min_cache_object_size;   /* in bytes */
    apr_size_t max_cache_object_size;   /* in bytes */
    apr_size_t max_cache_size;          /* in bytes */
    apr_size_t max_object_cnt;
    cache_pqueue_set_priority cache_remove_algorithm;

    /* maximum amount of data to buffer on a streamed response where
     * we haven't yet seen EOS */
    apr_off_t max_streaming_buffer_size;
} mem_cache_conf;
static mem_cache_conf *sconf;

#define DEFAULT_MAX_CACHE_SIZE 100*1024
#define DEFAULT_MIN_CACHE_OBJECT_SIZE 0
#define DEFAULT_MAX_CACHE_OBJECT_SIZE 10000
#define DEFAULT_MAX_OBJECT_CNT 1009
#define DEFAULT_MAX_STREAMING_BUFFER_SIZE 100000
#define CACHEFILE_LEN 20

/* Forward declarations */
static int remove_entity(cache_handle_t *h);
static apr_status_t store_headers(cache_handle_t *h, request_rec *r, cache_info *i);
static apr_status_t store_body(cache_handle_t *h, request_rec *r, apr_bucket_brigade *b);
static apr_status_t recall_headers(cache_handle_t *h, request_rec *r);
static apr_status_t recall_body(cache_handle_t *h, apr_pool_t *p, apr_bucket_brigade *bb);

static void cleanup_cache_object(cache_object_t *obj);

static long memcache_get_priority(void*a)
{
    cache_object_t *obj = (cache_object_t *)a;
    mem_cache_object_t *mobj = obj->vobj;

    return  mobj->priority;
}

static void memcache_inc_frequency(void*a)
{
    cache_object_t *obj = (cache_object_t *)a;
    mem_cache_object_t *mobj = obj->vobj;

    mobj->total_refs++;
    mobj->priority = 0;
}

static void memcache_set_pos(void *a, apr_ssize_t pos)
{
    cache_object_t *obj = (cache_object_t *)a;
    mem_cache_object_t *mobj = obj->vobj;

    apr_atomic_set(&mobj->pos, pos);
}
static apr_ssize_t memcache_get_pos(void *a)
{
    cache_object_t *obj = (cache_object_t *)a;
    mem_cache_object_t *mobj = obj->vobj;

    return apr_atomic_read(&mobj->pos);
}

static apr_size_t memcache_cache_get_size(void*a)
{
    cache_object_t *obj = (cache_object_t *)a;
    mem_cache_object_t *mobj = obj->vobj;
    return mobj->m_len;
}
/** callback to get the key of a item */
static const char* memcache_cache_get_key(void*a)
{
    cache_object_t *obj = (cache_object_t *)a;
    return obj->key;
}
/** 
 * memcache_cache_free()
 * memcache_cache_free is a callback that is only invoked by a thread 
 * running in cache_insert(). cache_insert() runs under protection
 * of sconf->lock.  By the time this function has been entered, the cache_object
 * has been ejected from the cache. decrement the refcount and if the refcount drops
 * to 0, cleanup the cache object.
 */
static void memcache_cache_free(void*a)
{
    cache_object_t *obj = (cache_object_t *)a;

    /* Decrement the refcount to account for the object being ejected
     * from the cache. If the refcount is 0, free the object.
     */
    if (!apr_atomic_dec(&obj->refcount)) {
        cleanup_cache_object(obj);
    }
}
/*
 * functions return a 'negative' score since priority queues
 * dequeue the object with the highest value first
 */
static long memcache_lru_algorithm(long queue_clock, void *a) 
{
    cache_object_t *obj = (cache_object_t *)a;
    mem_cache_object_t *mobj = obj->vobj;
    if (mobj->priority == 0)
        mobj->priority = queue_clock - mobj->total_refs;

    /*	
     * a 'proper' LRU function would just be
     *  mobj->priority = mobj->total_refs; 
     */
    return mobj->priority;
}

static long memcache_gdsf_algorithm(long queue_clock, void *a) 
{
    cache_object_t *obj = (cache_object_t *)a;
    mem_cache_object_t *mobj = obj->vobj;

    if (mobj->priority == 0)
        mobj->priority = queue_clock -
                           (long)(mobj->total_refs*1000 / mobj->m_len);

    return mobj->priority;
}

static void cleanup_cache_object(cache_object_t *obj)
{
    mem_cache_object_t *mobj = obj->vobj;

    /* TODO:
     * We desperately need a more efficient way of allocating objects. We're
     * making way too many malloc calls to create a fully populated 
     * cache object...
     */

    /* Cleanup the cache_object_t */
    if (obj->key) {
        free(obj->key);
    }
    if (obj->info.content_type) {
        free(obj->info.content_type);
    }
    if (obj->info.etag) {
        free(obj->info.etag);
    }
    if (obj->info.lastmods) {
        free(obj->info.lastmods);
    }
    if (obj->info.filename) {
        free(obj->info.filename);
    }

    free(obj);
    
    /* Cleanup the mem_cache_object_t */
    if (mobj) {
        if (mobj->type == CACHE_TYPE_HEAP && mobj->m) {
            free(mobj->m);
        }
        if (mobj->type == CACHE_TYPE_FILE && mobj->fd) {
#ifdef WIN32
            CloseHandle(mobj->fd);
#else
            close(mobj->fd);
#endif
        }
        if (mobj->header_out) {
            if (mobj->header_out[0].hdr) 
                free(mobj->header_out[0].hdr);
            free(mobj->header_out);
        }
        if (mobj->err_header_out) {
            if (mobj->err_header_out[0].hdr) 
                free(mobj->err_header_out[0].hdr);
            free(mobj->err_header_out);
        }
        if (mobj->subprocess_env) {
            if (mobj->subprocess_env[0].hdr) 
                free(mobj->subprocess_env[0].hdr);
            free(mobj->subprocess_env);
        }
        if (mobj->notes) {
            if (mobj->notes[0].hdr) 
                free(mobj->notes[0].hdr);
            free(mobj->notes);
        }
        if (mobj->req_hdrs) {
            if (mobj->req_hdrs[0].hdr)
                free(mobj->req_hdrs[0].hdr);
            free(mobj->req_hdrs);
        }
        free(mobj);
    }
}
static apr_status_t decrement_refcount(void *arg) 
{
    cache_object_t *obj = (cache_object_t *) arg;

    /* If obj->complete is not set, the cache update failed and the
     * object needs to be removed from the cache then cleaned up.
     * The garbage collector may have ejected the object from the
     * cache already, so make sure it is really still in the cache
     * before attempting to remove it.
     */
    if (!obj->complete) {
        cache_object_t *tobj = NULL;
        if (sconf->lock) {
            apr_thread_mutex_lock(sconf->lock);
        }
        tobj = cache_find(sconf->cache_cache, obj->key);
        if (tobj == obj) {
            cache_remove(sconf->cache_cache, obj);
            apr_atomic_dec(&obj->refcount);
        }
        if (sconf->lock) {
            apr_thread_mutex_unlock(sconf->lock);
        }
    } 

    /* If the refcount drops to 0, cleanup the cache object */
    if (!apr_atomic_dec(&obj->refcount)) {
        cleanup_cache_object(obj);
    }
    return APR_SUCCESS;
}
static apr_status_t cleanup_cache_mem(void *sconfv)
{
    cache_object_t *obj;
    mem_cache_conf *co = (mem_cache_conf*) sconfv;

    if (!co) {
        return APR_SUCCESS;
    }
    if (!co->cache_cache) {
        return APR_SUCCESS;
    }

    if (sconf->lock) {
        apr_thread_mutex_lock(sconf->lock);
    }
    obj = cache_pop(co->cache_cache);
    while (obj) {         
        /* Iterate over the cache and clean up each unreferenced entry */
        if (!apr_atomic_dec(&obj->refcount)) {
            cleanup_cache_object(obj);
        }
        obj = cache_pop(co->cache_cache);
    }

    /* Cache is empty, free the cache table */        
    cache_free(co->cache_cache);

    if (sconf->lock) {
        apr_thread_mutex_unlock(sconf->lock);
    }
    return APR_SUCCESS;
}
/*
 * TODO: enable directives to be overridden in various containers
 */
static void *create_cache_config(apr_pool_t *p, server_rec *s)
{
    sconf = apr_pcalloc(p, sizeof(mem_cache_conf));

    sconf->min_cache_object_size = DEFAULT_MIN_CACHE_OBJECT_SIZE;
    sconf->max_cache_object_size = DEFAULT_MAX_CACHE_OBJECT_SIZE;
    /* Number of objects in the cache */
    sconf->max_object_cnt = DEFAULT_MAX_OBJECT_CNT;
    /* Size of the cache in bytes */
    sconf->max_cache_size = DEFAULT_MAX_CACHE_SIZE;
    sconf->cache_cache = NULL;
    sconf->cache_remove_algorithm = memcache_gdsf_algorithm;
    sconf->max_streaming_buffer_size = DEFAULT_MAX_STREAMING_BUFFER_SIZE;

    return sconf;
}

static int create_entity(cache_handle_t *h, cache_type_e type_e,
                         request_rec *r, const char *key, apr_off_t len) 
{
    cache_object_t *obj, *tmp_obj;
    mem_cache_object_t *mobj;
    apr_size_t key_len;

    if (len == -1) {
        /* Caching a streaming response. Assume the response is
         * less than or equal to max_streaming_buffer_size. We will
         * correct all the cache size counters in store_body once
         * we know exactly know how much we are caching.
         */
        len = sconf->max_streaming_buffer_size;
    }

    /* Note: cache_insert() will automatically garbage collect 
     * objects from the cache if the max_cache_size threshold is
     * exceeded. This means mod_mem_cache does not need to implement
     * max_cache_size checks.
     */
    if (len < sconf->min_cache_object_size || 
        len > sconf->max_cache_object_size) {
        ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, r->server,
                     "mem_cache: URL %s failed the size check and will not be cached.",
                     key);
        return DECLINED;
    }

    if (type_e == CACHE_TYPE_FILE) {
        /* CACHE_TYPE_FILE is only valid for local content handled by the 
         * default handler. Need a better way to check if the file is
         * local or not.