00001 /******************************************************************************* 00002 00003 @file ICache.d 00004 00005 Copyright (c) 2004 Kris Bell 00006 00007 This software is provided 'as-is', without any express or implied 00008 warranty. In no event will the authors be held liable for damages 00009 of any kind arising from the use of this software. 00010 00011 Permission is hereby granted to anyone to use this software for any 00012 purpose, including commercial applications, and to alter it and/or 00013 redistribute it freely, subject to the following restrictions: 00014 00015 1. The origin of this software must not be misrepresented; you must 00016 not claim that you wrote the original software. If you use this 00017 software in a product, an acknowledgment within documentation of 00018 said product would be appreciated but is not required. 00019 00020 2. Altered source versions must be plainly marked as such, and must 00021 not be misrepresented as being the original software. 00022 00023 3. This notice may not be removed or altered from any distribution 00024 of the source. 00025 00026 4. Derivative works are permitted, but they must carry this notice 00027 in full and credit the original source. 00028 00029 00030 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 00031 00032 00033 @version Initial version, April 2004 00034 @author Kris 00035 00036 00037 *******************************************************************************/ 00038 00039 module mango.cache.model.ICache; 00040 00041 private import mango.cache.model.IPayload; 00042 00043 /****************************************************************************** 00044 00045 Defines what a cache instance exposes. We try to keep the basic 00046 operations to a reasonable minimum. 00047 00048 ******************************************************************************/ 00049 00050 interface ICache 00051 { 00052 /********************************************************************** 00053 00054 Get the cache entry identified by the given key 00055 00056 **********************************************************************/ 00057 00058 IPayload get (char[] key); 00059 } 00060 00061 00062 /****************************************************************************** 00063 00064 Defines what a modifiable cache instance exposes 00065 00066 ******************************************************************************/ 00067 00068 interface IMutableCache : ICache 00069 { 00070 /********************************************************************** 00071 00072 Place an entry into the cache and associate it with the 00073 provided key. Note that there can be only one entry for 00074 any particular key. If two keys entries are added with 00075 the same key, the second effectively overwrites the first. 00076 00077 Returns what it was given 00078 00079 **********************************************************************/ 00080 00081 IPayload put (char[] key, IPayload entry); 00082 00083 /********************************************************************** 00084 00085 Remove (and return) the cache entry associated with the 00086 provided key. The entry will not be removed if it's time 00087 attribute is newer than the (optional) specified 'timelimit'. 00088 00089 Returns null if there is no such entry. 00090 00091 **********************************************************************/ 00092 00093 IPayload extract (char[] key, ulong timeLimit = ulong.max); 00094 00095 /********************************************************************** 00096 00097 This is a factory for producing an ICache instance upon 00098 the cache content. The provided loader will populate the 00099 cache whenever a stale or missing entry is seen 00100 00101 **********************************************************************/ 00102 00103 ICache bind (ICacheLoader loader); 00104 } 00105 00106 00107 /****************************************************************************** 00108 00109 Manages the lifespan of an ICache entry. These loaders effectively 00110 isolate the cache from whence the content is derived. It's a good 00111 idea to employ this abstraction where appropriate, since it allows 00112 the cache source to change with minimal (if any) impact on client 00113 code. 00114 00115 ******************************************************************************/ 00116 00117 interface ICacheLoader 00118 { 00119 /********************************************************************** 00120 00121 Test the cache entry to see if it is still valid. A true 00122 return value indicates the entry is valid, whereas false 00123 flags the entry as stale. The latter case will cause the 00124 load() method to be invoked. 00125 00126 **********************************************************************/ 00127 00128 bool test (IPayload p); 00129 00130 /********************************************************************** 00131 00132 Load a cache entry from wherever the content is persisted. 00133 The 'time' argument represents that belonging to a stale 00134 entry, which can be used to optimize the loader operation 00135 (no need to perform a full load where there's already a 00136 newer version in an L2 cache). This 'time' value will be 00137 long.min where was no such stale entry. 00138 00139 **********************************************************************/ 00140 00141 IPayload load (char[] key, long time); 00142 } 00143 00144 00145 /****************************************************************************** 00146 00147 Manages the loading of ICache entries remotely, on the device 00148 that actually contains the remote cache entry. The benefit of 00149 this approach lies in the ability to 'gate' access to specific 00150 resources across the entire network. That is; where particular 00151 entries are prohibitively costly to construct, it's worthwhile 00152 ensuring that cost is reduced to a bare minimum. These remote 00153 loaders allow the cache host to block multiple network clients 00154 until there's a new entry available. Without this mechanism, 00155 it's possible for multiple network clients to request the same 00156 entry simultaneously; therefore increasing the overall cost. 00157 The end result is similar to that of a distributed-transaction. 00158 00159 ******************************************************************************/ 00160 00161 interface IRemoteCacheLoader : IPayload, ICacheLoader 00162 { 00163 /********************************************************************** 00164 00165 Return the sleep duration between attempts to retrieve 00166 a locked cache entry. Consider setting this duration to 00167 be approximately half the time you'd expect each remote 00168 cache-load to typically consume. The 'wait' argument is 00169 a representation of how many microseconds have added up 00170 while waiting. When this value exceeds some limit, you 00171 should return zero to indicate a timeout condition. 00172 00173 Note that the return value should be in microseconds ~ 00174 one tenth of a second equals 100_000 microseconds. Note 00175 also that you might consider returning a sliding value, 00176 where the pause starts off small, and increases as time 00177 passes. A simple implementation might look like this: 00178 00179 @code 00180 return (wait > 2_000_000) ? 0 : 10_000 + wait / 2; 00181 @endcode 00182 00183 **********************************************************************/ 00184 00185 uint pause (uint wait); 00186 } 00187