| Zsolt Haraszti | cd22adc | 2016-10-25 00:13:06 -0700 | [diff] [blame] | 1 | # |
| 2 | # Copyright 2016 the original author or authors. |
| 3 | # |
| 4 | # Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | # you may not use this file except in compliance with the License. |
| 6 | # You may obtain a copy of the License at |
| 7 | # |
| 8 | # http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | # |
| 10 | # Unless required by applicable law or agreed to in writing, software |
| 11 | # distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | # See the License for the specific language governing permissions and |
| 14 | # limitations under the License. |
| 15 | # |
| 16 | |
| 17 | """ |
| 18 | Utilities to handle gRPC server and client side code in a Twisted environment |
| 19 | """ |
| 20 | from concurrent.futures import Future |
| 21 | from twisted.internet import reactor |
| 22 | from twisted.internet.defer import Deferred |
| 23 | |
| 24 | |
| 25 | def twisted_async(func): |
| 26 | """ |
| 27 | This decorator can be used to implement a gRPC method on the twisted |
| 28 | thread, allowing asynchronous programming in Twisted while serving |
| 29 | a gRPC call. |
| 30 | |
| 31 | gRPC methods normally are called on the futures.ThreadPool threads, |
| 32 | so these methods cannot directly use Twisted protocol constructs. |
| 33 | If the implementation of the methods needs to touch Twisted, it is |
| 34 | safer (or mandatory) to wrap the method with this decorator, which will |
| 35 | call the inner method from the external thread and ensure that the |
| 36 | result is passed back to the foreign thread. |
| 37 | |
| 38 | Example usage: |
| 39 | |
| 40 | When implementing a gRPC server, typical pattern is: |
| 41 | |
| 42 | class SpamService(SpamServicer): |
| 43 | |
| 44 | def GetBadSpam(self, request, context): |
| 45 | '''this is called from a ThreadPoolExecutor thread''' |
| 46 | # generally unsafe to make Twisted calls |
| 47 | |
| 48 | @twisted_async |
| 49 | def GetSpamSafely(self, request, context): |
| 50 | '''this method now is executed on the Twisted main thread |
| 51 | # safe to call any Twisted protocol functions |
| 52 | |
| 53 | @twisted_async |
| 54 | @inlineCallbacks |
| 55 | def GetAsyncSpam(self, request, context): |
| 56 | '''this generator can use inlineCallbacks Twisted style''' |
| 57 | result = yield some_async_twisted_call(request) |
| 58 | returnValue(result) |
| 59 | |
| 60 | """ |
| 61 | def in_thread_wrapper(*args, **kw): |
| 62 | |
| 63 | f = Future() |
| 64 | |
| 65 | def twisted_wrapper(): |
| 66 | try: |
| 67 | d = func(*args, **kw) |
| 68 | if isinstance(d, Deferred): |
| 69 | |
| 70 | def _done(result): |
| 71 | f.set_result(result) |
| 72 | f.done() |
| 73 | |
| 74 | def _error(e): |
| 75 | f.set_exception(e) |
| 76 | f.done() |
| 77 | |
| 78 | d.addCallback(_done) |
| 79 | d.addErrback(_error) |
| 80 | |
| 81 | else: |
| 82 | f.set_result(d) |
| 83 | f.done() |
| 84 | |
| 85 | except Exception, e: |
| 86 | f.set_exception(e) |
| 87 | f.done() |
| 88 | |
| 89 | reactor.callFromThread(twisted_wrapper) |
| 90 | result = f.result() |
| 91 | |
| 92 | return result |
| 93 | |
| 94 | return in_thread_wrapper |
| 95 | |
| 96 | |