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Diffstat (limited to 'subversion/libsvn_subr/cache_config.c')
| -rw-r--r-- | subversion/libsvn_subr/cache_config.c | 169 |
1 files changed, 169 insertions, 0 deletions
diff --git a/subversion/libsvn_subr/cache_config.c b/subversion/libsvn_subr/cache_config.c new file mode 100644 index 0000000..86c12dc --- /dev/null +++ b/subversion/libsvn_subr/cache_config.c @@ -0,0 +1,169 @@ +/* svn_cache_config.c : configuration of internal caches + * + * ==================================================================== + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you 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. + * ==================================================================== + */ + +#include <apr_atomic.h> + +#include "svn_cache_config.h" +#include "private/svn_cache.h" + +#include "svn_pools.h" + +/* The cache settings as a process-wide singleton. + */ +static svn_cache_config_t cache_settings = + { + /* default configuration: + * + * Please note that the resources listed below will be allocated + * PER PROCESS. Thus, the defaults chosen here are kept deliberately + * low to still make a difference yet to ensure that pre-fork servers + * on machines with small amounts of RAM aren't severely impacted. + */ + 0x1000000, /* 16 MB for caches. + * If you are running a single server process, + * you may easily increase that to 50+% of your RAM + * using svn_fs_set_cache_config(). + */ + 16, /* up to 16 files kept open. + * Most OS restrict the number of open file handles to + * about 1000. To minimize I/O and OS overhead, values + * of 500+ can be beneficial (use svn_fs_set_cache_config() + * to change the configuration). + * When running with a huge in-process cache, this number + * has little impact on performance and a more modest + * value (< 100) may be more suitable. + */ +#if APR_HAS_THREADS + FALSE /* assume multi-threaded operation. + * Because this simply activates proper synchronization + * between threads, it is a safe default. + */ +#else + TRUE /* single-threaded is the only supported mode of operation */ +#endif +}; + +/* Get the current FSFS cache configuration. */ +const svn_cache_config_t * +svn_cache_config_get(void) +{ + return &cache_settings; +} + +/* Access the process-global (singleton) membuffer cache. The first call + * will automatically allocate the cache using the current cache config. + * NULL will be returned if the desired cache size is 0 or if the cache + * could not be created for some reason. + */ +svn_membuffer_t * +svn_cache__get_global_membuffer_cache(void) +{ + static svn_membuffer_t * volatile cache = NULL; + + apr_uint64_t cache_size = cache_settings.cache_size; + if (!cache && cache_size) + { + svn_error_t *err; + + svn_membuffer_t *old_cache = NULL; + svn_membuffer_t *new_cache = NULL; + + /* auto-allocate cache */ + apr_allocator_t *allocator = NULL; + apr_pool_t *pool = NULL; + + if (apr_allocator_create(&allocator)) + return NULL; + + /* Ensure that we free partially allocated data if we run OOM + * before the cache is complete: If the cache cannot be allocated + * in its full size, the create() function will clear the pool + * explicitly. The allocator will make sure that any memory no + * longer used by the pool will actually be returned to the OS. + * + * Please note that this pool and allocator is used *only* to + * allocate the large membuffer. All later dynamic allocations + * come from other, temporary pools and allocators. + */ + apr_allocator_max_free_set(allocator, 1); + + /* don't terminate upon OOM but make pool return a NULL pointer + * instead so we can disable caching gracefully and continue + * operation without membuffer caches. + */ + apr_pool_create_ex(&pool, NULL, NULL, allocator); + if (pool == NULL) + return NULL; + apr_allocator_owner_set(allocator, pool); + + err = svn_cache__membuffer_cache_create( + &new_cache, + (apr_size_t)cache_size, + (apr_size_t)(cache_size / 10), + 0, + ! svn_cache_config_get()->single_threaded, + FALSE, + pool); + + /* Some error occurred. Most likely it's an OOM error but we don't + * really care. Simply release all cache memory and disable caching + */ + if (err) + { + /* Memory and error cleanup */ + svn_error_clear(err); + svn_pool_destroy(pool); + + /* Prevent future attempts to create the cache. However, an + * existing cache instance (see next comment) remains valid. + */ + cache_settings.cache_size = 0; + + /* The current caller won't get the cache object. + * However, a concurrent call might have succeeded in creating + * the cache object. That call and all following ones will then + * use the successfully created cache instance. + */ + return NULL; + } + + /* Handle race condition: if we are the first to create a + * cache object, make it our global singleton. Otherwise, + * discard the new cache and keep the existing one. + * + * Cast is necessary because of APR bug: + * https://issues.apache.org/bugzilla/show_bug.cgi?id=50731 + */ + old_cache = apr_atomic_casptr((volatile void **)&cache, new_cache, NULL); + if (old_cache != NULL) + svn_pool_destroy(pool); + } + + return cache; +} + +void +svn_cache_config_set(const svn_cache_config_t *settings) +{ + cache_settings = *settings; +} + |
