[ESI][Cosim][NFC] Refactor cosim to divorce capnp from DPI (#7045)

Move generic functionality into Capnp library. This divorces it from the
DPI server, allowing other things to use it. Additionally, divorce
server from general functionality to make adding a client thread easier.

lib/Dialect/ESI/runtime/cosim/CMakeLists.txt

@@ -18,6 +18,10 @@ add_library(EsiCosimCapnp SHARED
   ${COSIM_CAPNP_HDRS}
   ${COSIM_CAPNP_SRCS}
   ${COSIM_SCHEMA_HDR}
+
+  lib/CapnpThreads.cpp
+  lib/Endpoint.cpp
+  lib/Server.cpp
 )
 target_include_directories(EsiCosimCapnp PUBLIC ${CAPNPC_OUTPUT_DIR})
 target_include_directories(EsiCosimCapnp PUBLIC ${CAPNP_INCLUDE_DIRS})

lib/Dialect/ESI/runtime/cosim/cosim_dpi_server/CMakeLists.txt

@@ -6,8 +6,6 @@
 
 add_library(EsiCosimDpiServer SHARED
   DpiEntryPoints.cpp
-  Server.cpp
-  Endpoint.cpp
 )
 set_target_properties(EsiCosimDpiServer
     PROPERTIES

lib/Dialect/ESI/runtime/cosim/cosim_dpi_server/DpiEntryPoints.cpp

@@ -16,8 +16,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "cosim/Server.h"
-#include "cosim/dpi.h"
+#include "cosim/CapnpThreads.h"
+#include "dpi.h"
 
 #include <algorithm>
 #include <cassert>

lib/Dialect/ESI/runtime/cosim/include/cosim/CapnpThreads.h

@@ -1,4 +1,4 @@
-//===- Server.h - ESI cosim RPC servers -------------------------*- C++ -*-===//
+//===- CapnpThreads.h - ESI cosim RPC ---------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -20,24 +20,46 @@
 #include "cosim/LowLevel.h"
 #include <thread>
 
+namespace kj {
+class WaitScope;
+} // namespace kj
+
 namespace esi {
 namespace cosim {
 
+/// Since Capnp is not thread-safe, client and server must be run in their own
+/// threads and communicate with the outside world through thread safe channels.
+class CapnpCosimThread {
+public:
+  EndpointRegistry endpoints;
+  LowLevel lowLevelBridge;
+
+  CapnpCosimThread();
+  ~CapnpCosimThread();
+
+  /// Stop the thread. This is a blocking call -- it will not return until the
+  /// capnp thread has stopped.
+  void stop();
+
+protected:
+  /// Start capnp polling loop. Does not return until stop() is called. Must be
+  /// called in the same thread the RPC server/client was created.
+  void loop(kj::WaitScope &waitScope);
+
+  using Lock = std::lock_guard<std::mutex>;
+  std::thread *myThread;
+  volatile bool stopSig;
+  std::mutex m;
+};
+
 /// The main RpcServer. Does not implement any capnp RPC interfaces but contains
 /// the capnp main RPC server. We run the capnp server in its own thread to be
 /// more responsive to network traffic and so as to not slow down the
 /// simulation.
-class RpcServer {
+class RpcServer : public CapnpCosimThread {
 public:
-  EndpointRegistry endpoints;
-  LowLevel lowLevelBridge;
-
-  RpcServer();
-  ~RpcServer();
-
   /// Start and stop the server thread.
   void run(uint16_t port);
-  void stop();
 
   void setManifest(unsigned int esiVersion,
                    const std::vector<uint8_t> &manifest) {
@@ -46,15 +68,9 @@ public:
   }
 
 private:
-  using Lock = std::lock_guard<std::mutex>;
-
   /// The thread's main loop function. Exits on shutdown.
   void mainLoop(uint16_t port);
 
-  std::thread *mainThread;
-  volatile bool stopSig;
-  std::mutex m;
-
   unsigned int esiVersion = -1;
   std::vector<uint8_t> compressedManifest;
 };

lib/Dialect/ESI/runtime/cosim/lib/CapnpThreads.cpp

@@ -0,0 +1,51 @@
+//===- CapnpThreads.cpp - Cosim RPC common code -----------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "cosim/CapnpThreads.h"
+#include "CosimDpi.capnp.h"
+#include <capnp/ez-rpc.h>
+#include <thread>
+#ifdef _WIN32
+#include <io.h>
+#else
+#include <unistd.h>
+#endif
+
+using namespace capnp;
+using namespace esi::cosim;
+
+CapnpCosimThread::CapnpCosimThread() : myThread(nullptr), stopSig(false) {}
+CapnpCosimThread::~CapnpCosimThread() { stop(); }
+
+void CapnpCosimThread::loop(kj::WaitScope &waitScope) {
+  // OK, this is uber hacky, but it unblocks me and isn't _too_ inefficient. The
+  // problem is that I can't figure out how read the stop signal from libkj
+  // asyncrony land.
+  //
+  // IIRC the main libkj wait loop uses `select()` (or something similar on
+  // Windows) on its FDs. As a result, any code which checks the stop variable
+  // doesn't run until there is some I/O. Probably the right way is to set up a
+  // pipe to deliver a shutdown signal.
+  //
+  // TODO: Figure out how to do this properly, if possible.
+  while (!stopSig) {
+    waitScope.poll();
+    std::this_thread::sleep_for(std::chrono::milliseconds(10));
+  }
+}
+
+/// Signal the RPC server thread to stop. Wait for it to exit.
+void CapnpCosimThread::stop() {
+  Lock g(m);
+  if (myThread == nullptr) {
+    fprintf(stderr, "CapnpCosimThread not Run()\n");
+  } else if (!stopSig) {
+    stopSig = true;
+    myThread->join();
+  }
+}

lib/Dialect/ESI/runtime/cosim/lib/Server.cpp

@@ -17,8 +17,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "cosim/Server.h"
 #include "CosimDpi.capnp.h"
+#include "cosim/CapnpThreads.h"
 #include <capnp/ez-rpc.h>
 #include <thread>
 #ifdef _WIN32
@@ -242,9 +242,6 @@ kj::Promise<void> CosimServer::openLowLevel(OpenLowLevelContext ctxt) {
 
 /// ----- RpcServer definitions.
 
-RpcServer::RpcServer() : mainThread(nullptr), stopSig(false) {}
-RpcServer::~RpcServer() { stop(); }
-
 /// Write the port number to a file. Necessary when we allow 'EzRpcServer' to
 /// select its own port. We can't use stdout/stderr because the flushing
 /// semantics are undefined (as in `flush()` doesn't work on all simulators).
@@ -268,40 +265,15 @@ void RpcServer::mainLoop(uint16_t port) {
   }
   writePort(port);
   printf("[COSIM] Listening on port: %u\n", (unsigned int)port);
-
-  // OK, this is uber hacky, but it unblocks me and isn't _too_ inefficient. The
-  // problem is that I can't figure out how read the stop signal from libkj
-  // asyncrony land.
-  //
-  // IIRC the main libkj wait loop uses `select()` (or something similar on
-  // Windows) on its FDs. As a result, any code which checks the stop variable
-  // doesn't run until there is some I/O. Probably the right way is to set up a
-  // pipe to deliver a shutdown signal.
-  //
-  // TODO: Figure out how to do this properly, if possible.
-  while (!stopSig) {
-    waitScope.poll();
-    std::this_thread::sleep_for(std::chrono::milliseconds(10));
-  }
+  loop(waitScope);
 }
 
 /// Start the server if not already started.
 void RpcServer::run(uint16_t port) {
   Lock g(m);
-  if (mainThread == nullptr) {
-    mainThread = new std::thread(&RpcServer::mainLoop, this, port);
+  if (myThread == nullptr) {
+    myThread = new std::thread(&RpcServer::mainLoop, this, port);
   } else {
     fprintf(stderr, "Warning: cannot Run() RPC server more than once!");
   }
 }
-
-/// Signal the RPC server thread to stop. Wait for it to exit.
-void RpcServer::stop() {
-  Lock g(m);
-  if (mainThread == nullptr) {
-    fprintf(stderr, "RpcServer not Run()\n");
-  } else if (!stopSig) {
-    stopSig = true;
-    mainThread->join();
-  }
-}