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1 | /* |
2 | * Licensed to the Apache Software Foundation (ASF) under one | |
3 | * or more contributor license agreements. See the NOTICE file | |
4 | * distributed with this work for additional information | |
5 | * regarding copyright ownership. The ASF licenses this file | |
6 | * to you under the Apache License, Version 2.0 (the | |
7 | * "License"); you may not use this file except in compliance | |
8 | * with the License. You may obtain a copy of the License at | |
9 | * | |
10 | * http://www.apache.org/licenses/LICENSE-2.0 | |
11 | * | |
12 | * Unless required by applicable law or agreed to in writing, | |
13 | * software distributed under the License is distributed on an | |
14 | * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | |
15 | * KIND, either express or implied. See the License for the | |
16 | * specific language governing permissions and limitations | |
17 | * under the License. | |
18 | */ | |
19 | module thrift.codegen.client_pool; | |
20 | ||
21 | import core.time : dur, Duration, TickDuration; | |
22 | import std.traits : ParameterTypeTuple, ReturnType; | |
23 | import thrift.base; | |
24 | import thrift.codegen.base; | |
25 | import thrift.codegen.client; | |
26 | import thrift.internal.codegen; | |
27 | import thrift.internal.resource_pool; | |
28 | ||
29 | /** | |
30 | * Manages a pool of TClients for the given interface, forwarding RPC calls to | |
31 | * members of the pool. | |
32 | * | |
33 | * If a request fails, another client from the pool is tried, and optionally, | |
34 | * a client is disabled for a configurable amount of time if it fails too | |
35 | * often. If all clients fail (and keepTrying is false), a | |
36 | * TCompoundOperationException is thrown, containing all the collected RPC | |
37 | * exceptions. | |
38 | */ | |
39 | class TClientPool(Interface) if (isService!Interface) : Interface { | |
40 | /// Shorthand for TClientBase!Interface, the client type this instance | |
41 | /// operates on. | |
42 | alias TClientBase!Interface Client; | |
43 | ||
44 | /** | |
45 | * Creates a new instance and adds the given clients to the pool. | |
46 | */ | |
47 | this(Client[] clients) { | |
48 | pool_ = new TResourcePool!Client(clients); | |
49 | ||
50 | rpcFaultFilter = (Exception e) { | |
51 | import thrift.protocol.base; | |
52 | import thrift.transport.base; | |
53 | return ( | |
54 | (cast(TTransportException)e !is null) || | |
55 | (cast(TApplicationException)e !is null) | |
56 | ); | |
57 | }; | |
58 | } | |
59 | ||
60 | /** | |
61 | * Executes an operation on the first currently active client. | |
62 | * | |
63 | * If the operation fails (throws an exception for which rpcFaultFilter is | |
64 | * true), the failure is recorded and the next client in the pool is tried. | |
65 | * | |
66 | * Throws: Any non-rpc exception that occurs, a TCompoundOperationException | |
67 | * if all clients failed with an rpc exception (if keepTrying is false). | |
68 | * | |
69 | * Example: | |
70 | * --- | |
71 | * interface Foo { string bar(); } | |
72 | * auto poolClient = tClientPool([tClient!Foo(someProtocol)]); | |
73 | * auto result = poolClient.execute((c){ return c.bar(); }); | |
74 | * --- | |
75 | */ | |
76 | ResultType execute(ResultType)(scope ResultType delegate(Client) work) { | |
77 | return executeOnPool!Client(work); | |
78 | } | |
79 | ||
80 | /** | |
81 | * Adds a client to the pool. | |
82 | */ | |
83 | void addClient(Client client) { | |
84 | pool_.add(client); | |
85 | } | |
86 | ||
87 | /** | |
88 | * Removes a client from the pool. | |
89 | * | |
90 | * Returns: Whether the client was found in the pool. | |
91 | */ | |
92 | bool removeClient(Client client) { | |
93 | return pool_.remove(client); | |
94 | } | |
95 | ||
96 | mixin(poolForwardCode!Interface()); | |
97 | ||
98 | /// Whether to open the underlying transports of a client before trying to | |
99 | /// execute a method if they are not open. This is usually desirable | |
100 | /// because it allows e.g. to automatically reconnect to a remote server | |
101 | /// if the network connection is dropped. | |
102 | /// | |
103 | /// Defaults to true. | |
104 | bool reopenTransports = true; | |
105 | ||
106 | /// Called to determine whether an exception comes from a client from the | |
107 | /// pool not working properly, or if it an exception thrown at the | |
108 | /// application level. | |
109 | /// | |
110 | /// If the delegate returns true, the server/connection is considered to be | |
111 | /// at fault, if it returns false, the exception is just passed on to the | |
112 | /// caller. | |
113 | /// | |
114 | /// By default, returns true for instances of TTransportException and | |
115 | /// TApplicationException, false otherwise. | |
116 | bool delegate(Exception) rpcFaultFilter; | |
117 | ||
118 | /** | |
119 | * Whether to keep trying to find a working client if all have failed in a | |
120 | * row. | |
121 | * | |
122 | * Defaults to false. | |
123 | */ | |
124 | bool keepTrying() const @property { | |
125 | return pool_.cycle; | |
126 | } | |
127 | ||
128 | /// Ditto | |
129 | void keepTrying(bool value) @property { | |
130 | pool_.cycle = value; | |
131 | } | |
132 | ||
133 | /** | |
134 | * Whether to use a random permutation of the client pool on every call to | |
135 | * execute(). This can be used e.g. as a simple form of load balancing. | |
136 | * | |
137 | * Defaults to true. | |
138 | */ | |
139 | bool permuteClients() const @property { | |
140 | return pool_.permute; | |
141 | } | |
142 | ||
143 | /// Ditto | |
144 | void permuteClients(bool value) @property { | |
145 | pool_.permute = value; | |
146 | } | |
147 | ||
148 | /** | |
149 | * The number of consecutive faults after which a client is disabled until | |
150 | * faultDisableDuration has passed. 0 to never disable clients. | |
151 | * | |
152 | * Defaults to 0. | |
153 | */ | |
154 | ushort faultDisableCount() @property { | |
155 | return pool_.faultDisableCount; | |
156 | } | |
157 | ||
158 | /// Ditto | |
159 | void faultDisableCount(ushort value) @property { | |
160 | pool_.faultDisableCount = value; | |
161 | } | |
162 | ||
163 | /** | |
164 | * The duration for which a client is no longer considered after it has | |
165 | * failed too often. | |
166 | * | |
167 | * Defaults to one second. | |
168 | */ | |
169 | Duration faultDisableDuration() @property { | |
170 | return pool_.faultDisableDuration; | |
171 | } | |
172 | ||
173 | /// Ditto | |
174 | void faultDisableDuration(Duration value) @property { | |
175 | pool_.faultDisableDuration = value; | |
176 | } | |
177 | ||
178 | protected: | |
179 | ResultType executeOnPool(ResultType)(scope ResultType delegate(Client) work) { | |
180 | auto clients = pool_[]; | |
181 | if (clients.empty) { | |
182 | throw new TException("No clients available to try."); | |
183 | } | |
184 | ||
185 | while (true) { | |
186 | Exception[] rpcExceptions; | |
187 | while (!clients.empty) { | |
188 | auto c = clients.front; | |
189 | clients.popFront; | |
190 | try { | |
191 | scope (success) { | |
192 | pool_.recordSuccess(c); | |
193 | } | |
194 | ||
195 | if (reopenTransports) { | |
196 | c.inputProtocol.transport.open(); | |
197 | c.outputProtocol.transport.open(); | |
198 | } | |
199 | ||
200 | return work(c); | |
201 | } catch (Exception e) { | |
202 | if (rpcFaultFilter && rpcFaultFilter(e)) { | |
203 | pool_.recordFault(c); | |
204 | rpcExceptions ~= e; | |
205 | } else { | |
206 | // We are dealing with a normal exception thrown by the | |
207 | // server-side method, just pass it on. As far as we are | |
208 | // concerned, the method call succeeded. | |
209 | pool_.recordSuccess(c); | |
210 | throw e; | |
211 | } | |
212 | } | |
213 | } | |
214 | ||
215 | // If we get here, no client succeeded during the current iteration. | |
216 | Duration waitTime; | |
217 | Client dummy; | |
218 | if (clients.willBecomeNonempty(dummy, waitTime)) { | |
219 | if (waitTime > dur!"hnsecs"(0)) { | |
220 | import core.thread; | |
221 | Thread.sleep(waitTime); | |
222 | } | |
223 | } else { | |
224 | throw new TCompoundOperationException("All clients failed.", | |
225 | rpcExceptions); | |
226 | } | |
227 | } | |
228 | } | |
229 | ||
230 | private: | |
231 | TResourcePool!Client pool_; | |
232 | } | |
233 | ||
234 | private { | |
235 | // Cannot use an anonymous delegate literal for this because they aren't | |
236 | // allowed in class scope. | |
237 | string poolForwardCode(Interface)() { | |
238 | string code = ""; | |
239 | ||
240 | foreach (methodName; AllMemberMethodNames!Interface) { | |
241 | enum qn = "Interface." ~ methodName; | |
242 | code ~= "ReturnType!(" ~ qn ~ ") " ~ methodName ~ | |
243 | "(ParameterTypeTuple!(" ~ qn ~ ") args) {\n"; | |
244 | code ~= "return executeOnPool((Client c){ return c." ~ | |
245 | methodName ~ "(args); });\n"; | |
246 | code ~= "}\n"; | |
247 | } | |
248 | ||
249 | return code; | |
250 | } | |
251 | } | |
252 | ||
253 | /** | |
254 | * TClientPool construction helper to avoid having to explicitly specify | |
255 | * the interface type, i.e. to allow the constructor being called using IFTI | |
256 | * (see $(DMDBUG 6082, D Bugzilla enhancement requet 6082)). | |
257 | */ | |
258 | TClientPool!Interface tClientPool(Interface)( | |
259 | TClientBase!Interface[] clients | |
260 | ) if (isService!Interface) { | |
261 | return new typeof(return)(clients); | |
262 | } |