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| 1 | +// Copyright (c) 2025 The Bitcoin Core developers |
| 2 | +// Distributed under the MIT software license, see the accompanying |
| 3 | +// file COPYING or http://www.opensource.org/licenses/mit-license.php. |
| 4 | + |
| 5 | +#ifndef MP_PROXY_TYPE_CONTEXT_H |
| 6 | +#define MP_PROXY_TYPE_CONTEXT_H |
| 7 | + |
| 8 | +#include <mp/proxy-io.h> |
| 9 | +#include <mp/util.h> |
| 10 | + |
| 11 | +namespace mp { |
| 12 | +template <typename Output> |
| 13 | +void CustomBuildField(TypeList<>, |
| 14 | + Priority<1>, |
| 15 | + ClientInvokeContext& invoke_context, |
| 16 | + Output&& output, |
| 17 | + typename std::enable_if<std::is_same<decltype(output.get()), Context::Builder>::value>::type* enable = nullptr) |
| 18 | +{ |
| 19 | + auto& connection = invoke_context.connection; |
| 20 | + auto& thread_context = invoke_context.thread_context; |
| 21 | + |
| 22 | + // Create local Thread::Server object corresponding to the current thread |
| 23 | + // and pass a Thread::Client reference to it in the Context.callbackThread |
| 24 | + // field so the function being called can make callbacks to this thread. |
| 25 | + // Also store the Thread::Client reference in the callback_threads map so |
| 26 | + // future calls over this connection can reuse it. |
| 27 | + auto [callback_thread, _]{SetThread( |
| 28 | + thread_context.callback_threads, thread_context.waiter->m_mutex, &connection, |
| 29 | + [&] { return connection. m_threads. add(kj::heap<ProxyServer<Thread>>(thread_context, std::thread{})); })}; |
| 30 | + |
| 31 | + // Call remote ThreadMap.makeThread function so server will create a |
| 32 | + // dedicated worker thread to run function calls from this thread. Store the |
| 33 | + // Thread::Client reference it returns in the request_threads map. |
| 34 | + auto make_request_thread{[&]{ |
| 35 | + // This code will only run if an IPC client call is being made for the |
| 36 | + // first time on this thread. After the first call, subsequent calls |
| 37 | + // will use the existing request thread. This code will also never run at |
| 38 | + // all if the current thread is a request thread created for a different |
| 39 | + // IPC client, because in that case PassField code (below) will have set |
| 40 | + // request_thread to point to the calling thread. |
| 41 | + auto request = connection.m_thread_map.makeThreadRequest(); |
| 42 | + request.setName(thread_context.thread_name); |
| 43 | + return request.send().getResult(); // Nonblocking due to capnp request pipelining. |
| 44 | + }}; |
| 45 | + auto [request_thread, _1]{SetThread( |
| 46 | + thread_context.request_threads, thread_context.waiter->m_mutex, |
| 47 | + &connection, make_request_thread)}; |
| 48 | + |
| 49 | + auto context = output.init(); |
| 50 | + context.setThread(request_thread->second.m_client); |
| 51 | + context.setCallbackThread(callback_thread->second.m_client); |
| 52 | +} |
| 53 | + |
| 54 | +//! PassField override for mp.Context arguments. Return asynchronously and call |
| 55 | +//! function on other thread found in context. |
| 56 | +template <typename Accessor, typename ServerContext, typename Fn, typename... Args> |
| 57 | +auto PassField(Priority<1>, TypeList<>, ServerContext& server_context, const Fn& fn, Args&&... args) -> |
| 58 | + typename std::enable_if< |
| 59 | + std::is_same<decltype(Accessor::get(server_context.call_context.getParams())), Context::Reader>::value, |
| 60 | + kj::Promise<typename ServerContext::CallContext>>::type |
| 61 | +{ |
| 62 | + const auto& params = server_context.call_context.getParams(); |
| 63 | + Context::Reader context_arg = Accessor::get(params); |
| 64 | + auto future = kj::newPromiseAndFulfiller<typename ServerContext::CallContext>(); |
| 65 | + auto& server = server_context.proxy_server; |
| 66 | + int req = server_context.req; |
| 67 | + auto invoke = MakeAsyncCallable( |
| 68 | + [fulfiller = kj::mv(future.fulfiller), |
| 69 | + call_context = kj::mv(server_context.call_context), &server, req, fn, args...]() mutable { |
| 70 | + const auto& params = call_context.getParams(); |
| 71 | + Context::Reader context_arg = Accessor::get(params); |
| 72 | + ServerContext server_context{server, call_context, req}; |
| 73 | + bool disconnected{false}; |
| 74 | + { |
| 75 | + // Before invoking the function, store a reference to the |
| 76 | + // callbackThread provided by the client in the |
| 77 | + // thread_local.request_threads map. This way, if this |
| 78 | + // server thread needs to execute any RPCs that call back to |
| 79 | + // the client, they will happen on the same client thread |
| 80 | + // that is waiting for this function, just like what would |
| 81 | + // happen if this were a normal function call made on the |
| 82 | + // local stack. |
| 83 | + // |
| 84 | + // If the request_threads map already has an entry for this |
| 85 | + // connection, it will be left unchanged, and it indicates |
| 86 | + // that the current thread is an RPC client thread which is |
| 87 | + // in the middle of an RPC call, and the current RPC call is |
| 88 | + // a nested call from the remote thread handling that RPC |
| 89 | + // call. In this case, the callbackThread value should point |
| 90 | + // to the same thread already in the map, so there is no |
| 91 | + // need to update the map. |
| 92 | + auto& thread_context = g_thread_context; |
| 93 | + auto& request_threads = thread_context.request_threads; |
| 94 | + auto [request_thread, inserted]{SetThread( |
| 95 | + request_threads, thread_context.waiter->m_mutex, |
| 96 | + server.m_context.connection, |
| 97 | + [&] { return context_arg.getCallbackThread(); })}; |
| 98 | + |
| 99 | + // If an entry was inserted into the requests_threads map, |
| 100 | + // remove it after calling fn.invoke. If an entry was not |
| 101 | + // inserted, one already existed, meaning this must be a |
| 102 | + // recursive call (IPC call calling back to the caller which |
| 103 | + // makes another IPC call), so avoid modifying the map. |
| 104 | + const bool erase_thread{inserted}; |
| 105 | + KJ_DEFER({ |
| 106 | + std::unique_lock<std::mutex> lock(thread_context.waiter->m_mutex); |
| 107 | + // Call erase here with a Connection* argument instead |
| 108 | + // of an iterator argument, because the `request_thread` |
| 109 | + // iterator may be invalid if the connection is closed |
| 110 | + // during this function call. More specifically, the |
| 111 | + // iterator may be invalid because SetThread adds a |
| 112 | + // cleanup callback to the Connection destructor that |
| 113 | + // erases the thread from the map, and also because the |
| 114 | + // ProxyServer<Thread> destructor calls |
| 115 | + // request_threads.clear(). |
| 116 | + if (erase_thread) { |
| 117 | + disconnected = !request_threads.erase(server.m_context.connection); |
| 118 | + } else { |
| 119 | + disconnected = !request_threads.count(server.m_context.connection); |
| 120 | + } |
| 121 | + }); |
| 122 | + fn.invoke(server_context, args...); |
| 123 | + } |
| 124 | + if (disconnected) { |
| 125 | + // If disconnected is true, the Connection object was |
| 126 | + // destroyed during the method call. Deal with this by |
| 127 | + // returning without ever fulfilling the promise, which will |
| 128 | + // cause the ProxyServer object to leak. This is not ideal, |
| 129 | + // but fixing the leak will require nontrivial code changes |
| 130 | + // because there is a lot of code assuming ProxyServer |
| 131 | + // objects are destroyed before Connection objects. |
| 132 | + return; |
| 133 | + } |
| 134 | + KJ_IF_MAYBE(exception, kj::runCatchingExceptions([&]() { |
| 135 | + server.m_context.connection->m_loop.sync([&] { |
| 136 | + auto fulfiller_dispose = kj::mv(fulfiller); |
| 137 | + fulfiller_dispose->fulfill(kj::mv(call_context)); |
| 138 | + }); |
| 139 | + })) |
| 140 | + { |
| 141 | + server.m_context.connection->m_loop.sync([&]() { |
| 142 | + auto fulfiller_dispose = kj::mv(fulfiller); |
| 143 | + fulfiller_dispose->reject(kj::mv(*exception)); |
| 144 | + }); |
| 145 | + } |
| 146 | + }); |
| 147 | + |
| 148 | + // Lookup Thread object specified by the client. The specified thread should |
| 149 | + // be a local Thread::Server object, but it needs to be looked up |
| 150 | + // asynchronously with getLocalServer(). |
| 151 | + auto thread_client = context_arg.getThread(); |
| 152 | + return server.m_context.connection->m_threads.getLocalServer(thread_client) |
| 153 | + .then([&server, invoke, req](const kj::Maybe<Thread::Server&>& perhaps) { |
| 154 | + // Assuming the thread object is found, pass it a pointer to the |
| 155 | + // `invoke` lambda above which will invoke the function on that |
| 156 | + // thread. |
| 157 | + KJ_IF_MAYBE (thread_server, perhaps) { |
| 158 | + const auto& thread = static_cast<ProxyServer<Thread>&>(*thread_server); |
| 159 | + server.m_context.connection->m_loop.log() |
| 160 | + << "IPC server post request #" << req << " {" << thread.m_thread_context.thread_name << "}"; |
| 161 | + thread.m_thread_context.waiter->post(std::move(invoke)); |
| 162 | + } else { |
| 163 | + server.m_context.connection->m_loop.log() |
| 164 | + << "IPC server error request #" << req << ", missing thread to execute request"; |
| 165 | + throw std::runtime_error("invalid thread handle"); |
| 166 | + } |
| 167 | + }) |
| 168 | + // Wait for the invocation to finish before returning to the caller. |
| 169 | + .then([invoke_wait = kj::mv(future.promise)]() mutable { return kj::mv(invoke_wait); }); |
| 170 | +} |
| 171 | +} // namespace mp |
| 172 | + |
| 173 | +#endif // MP_PROXY_TYPE_CONTEXT_H |
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