ceph/src/seastar/demos/sharded_parameter_demo.cc

   1 /*
   2  * This file is open source software, licensed to you under the terms
   3  * of the Apache License, Version 2.0 (the "License").  See the NOTICE file
   4  * distributed with this work for additional information regarding copyright
   5  * ownership.  You may not use this file except in compliance with the License.
   6  *
   7  * You may obtain a copy of the License at
   8  *
   9  *   http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing,
  12  * software distributed under the License is distributed on an
  13  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  14  * KIND, either express or implied.  See the License for the
  15  * specific language governing permissions and limitations
  16  * under the License.
  17  */
  18 /*
  19  * Copyright 2020 ScyllaDB
  20  */
  21
  22
  23 // Demonstration of seastar::sharded_parameter
  24
  25 #include <seastar/core/sharded.hh>
  26 #include <seastar/core/app-template.hh>
  27 #include <seastar/core/thread.hh>
  28 #include <seastar/util/defer.hh>
  29 #include <cassert>
  30
  31 // This is some service that we wish to run on all shards.
  32 class service_one {
  33     int _capacity = 7;
  34 public:
  35     // Pretend that this int is some important resource.
  36     int get_capacity() const { return _capacity; }
  37 };
  38
  39 // Another service that we run on all shards, that depends on service_one.
  40 class service_two {
  41     int _resource_allocation;
  42 public:
  43     service_two(service_one& s1, int resource_allocation) : _resource_allocation(resource_allocation) {}
  44     int get_resource_allocation() const { return _resource_allocation; }
  45 };
  46
  47 int main(int ac, char** av) {
  48     seastar::app_template app;
  49     return app.run(ac, av, [&] {
  50         // sharded<> setup code is typically run in a seastar::thread
  51         return seastar::async([&] {
  52
  53             // Launch service_one
  54             seastar::sharded<service_one> s1;
  55             s1.start().get();
  56             auto stop_s1 = seastar::defer([&] { s1.stop().get(); });
  57
  58             auto calculate_half_capacity = [] (service_one& s1) {
  59                 return s1.get_capacity() / 2;
  60             };
  61
  62             // Launch service_two, passing it per-shard dependencies from s1
  63             seastar::sharded<service_two> s2;
  64             // Start s2, passing two parameters to service_two's constructor
  65             s2.start(
  66                     // Each service_two instance will get a reference to a service_one instance on the same shard
  67                     std::ref(s1),
  68                     // This calculation will be performed on each shard
  69                     seastar::sharded_parameter(calculate_half_capacity, std::ref(s1))
  70             ).get();
  71             seastar::defer([&] { s2.stop().get(); });
  72
  73             s2.invoke_on_all([] (service_two& s2) {
  74                 assert(s2.get_resource_allocation() == 3);
  75             }).get();
  76         });
  77     });
  78 }