subversion/libsvn_subr/dso.c

   1 /*
   2  * ====================================================================
   3  * Copyright (c) 2006 CollabNet.  All rights reserved.
   4  *
   5  * This software is licensed as described in the file COPYING, which
   6  * you should have received as part of this distribution.  The terms
   7  * are also available at http://subversion.tigris.org/license-1.html.
   8  * If newer versions of this license are posted there, you may use a
   9  * newer version instead, at your option.
  10  *
  11  * This software consists of voluntary contributions made by many
  12  * individuals.  For exact contribution history, see the revision
  13  * history and logs, available at http://subversion.tigris.org/.
  14  * ====================================================================
  15  */
  16
  17 #include <apr_thread_mutex.h>
  18 #include <apr_hash.h>
  19
  20 #include "svn_dso.h"
  21 #include "svn_pools.h"
  22 #include "svn_private_config.h"
  23
  24 /* A mutex to protect our global pool and cache. */
  25 #if APR_HAS_THREADS
  26 static apr_thread_mutex_t *dso_mutex;
  27 #endif
  28
  29 /* Global pool to allocate DSOs in. */
  30 static apr_pool_t *dso_pool;
  31
  32 /* Global cache for storing DSO objects. */
  33 static apr_hash_t *dso_cache;
  34
  35 /* Just an arbitrary location in memory... */
  36 static int not_there_sentinel;
  37
  38 /* A specific value we store in the dso_cache to indicate that the
  39    library wasn't found.  This keeps us from allocating extra memory
  40    from dso_pool when trying to find libraries we already know aren't
  41    there.  */
  42 #define NOT_THERE ((void *) &not_there_sentinel)
  43
  44 void
  45 svn_dso_initialize()
  46 {
  47   if (dso_pool)
  48     return;
  49
  50   dso_pool = svn_pool_create(NULL);
  51
  52 #if APR_HAS_THREADS
  53   apr_thread_mutex_create(&dso_mutex, APR_THREAD_MUTEX_DEFAULT, dso_pool);
  54 #endif
  55
  56   dso_cache = apr_hash_make(dso_pool);
  57 }
  58
  59 #if APR_HAS_DSO
  60 svn_error_t *
  61 svn_dso_load(apr_dso_handle_t **dso, const char *fname)
  62 {
  63   apr_status_t status;
  64
  65   if (! dso_pool)
  66     svn_dso_initialize();
  67
  68 #if APR_HAS_THREADS
  69   status = apr_thread_mutex_lock(dso_mutex);
  70   if (status)
  71     return svn_error_wrap_apr(status, _("Can't grab DSO mutex"));
  72 #endif
  73
  74   *dso = apr_hash_get(dso_cache, fname, APR_HASH_KEY_STRING);
  75
  76   /* First check to see if we've been through this before...  We do this
  77      to avoid calling apr_dso_load multiple times for a given library,
  78      which would result in wasting small amounts of memory each time. */
  79   if (*dso == NOT_THERE)
  80     {
  81       *dso = NULL;
  82 #if APR_HAS_THREADS
  83       status = apr_thread_mutex_unlock(dso_mutex);
  84       if (status)
  85         return svn_error_wrap_apr(status, _("Can't ungrab DSO mutex"));
  86 #endif
  87       return SVN_NO_ERROR;
  88     }
  89
  90   /* If we got nothing back from the cache, try and load the library. */
  91   if (! *dso)
  92     {
  93       status = apr_dso_load(dso, fname, dso_pool);
  94       if (status)
  95         {
  96           *dso = NULL;
  97
  98           /* It wasn't found, so set the special "we didn't find it" value. */
  99           apr_hash_set(dso_cache,
 100                        apr_pstrdup(dso_pool, fname),
 101                        APR_HASH_KEY_STRING,
 102                        NOT_THERE);
 103
 104 #if APR_HAS_THREADS
 105           status = apr_thread_mutex_unlock(dso_mutex);
 106           if (status)
 107             return svn_error_wrap_apr(status, _("Can't ungrab DSO mutex"));
 108 #endif
 109           return SVN_NO_ERROR;
 110         }
 111
 112       /* Stash the dso so we can use it next time. */
 113       apr_hash_set(dso_cache,
 114                    apr_pstrdup(dso_pool, fname),
 115                    APR_HASH_KEY_STRING,
 116                    *dso);
 117     }
 118
 119 #if APR_HAS_THREADS
 120   status = apr_thread_mutex_unlock(dso_mutex);
 121   if (status)
 122     return svn_error_wrap_apr(status, _("Can't ungrab DSO mutex"));
 123 #endif
 124
 125   return SVN_NO_ERROR;
 126 }
 127 #endif /* APR_HAS_DSO */