[clang] [llvm] [clang][MBD] set up module build daemon infrastructure (PR #67562)

[Michael Spencer via cfe-commits]

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@@ -0,0 +1,289 @@
+//===------- cc1modbuildd_main.cpp - Clang CC1 Module Build Daemon --------===//
+//
+// 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 "clang/Tooling/ModuleBuildDaemon/SocketSupport.h"
+#include "clang/Tooling/ModuleBuildDaemon/Utils.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/Signals.h"
+#include "llvm/Support/ThreadPool.h"
+
+#include <csignal>
+#include <cstdbool>
+#include <cstdio>
+#include <cstring>
+#include <fstream>
+#include <optional>
+#include <string>
+#include <system_error>
+
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <unistd.h>
+#endif
+
+using namespace llvm;
+using namespace clang::tooling::cc1modbuildd;
+
+// Create unbuffered STDOUT stream so that any logging done by the module build
+// daemon can be viewed without having to terminate the process
+static raw_fd_ostream &unbuff_outs() {
+  static raw_fd_ostream S(fileno(stdout), false, true);
+  return S;
+}
+
+static bool LogVerbose = false;
+static void logVerbose(const llvm::Twine &message) {
+  if (LogVerbose) {
+    unbuff_outs() << message << '\n';
+  }
+}
+
+static void modifySignals(decltype(SIG_DFL) handler) {
+
+  if (std::signal(SIGTERM, handler) == SIG_ERR) {
+    errs() << "failed to handle SIGTERM" << '\n';
+    exit(EXIT_FAILURE);
+  }
+
+  if (std::signal(SIGINT, handler) == SIG_ERR) {
+    errs() << "failed to handle SIGINT" << '\n';
+    exit(EXIT_FAILURE);
+  }
+
+#ifdef SIGHUP
+  if (::signal(SIGHUP, SIG_IGN) == SIG_ERR) {
+    errs() << "failed to handle SIGHUP" << '\n';
+    exit(EXIT_FAILURE);
+  }
+#endif
+}
+
+namespace {
+
+class ModuleBuildDaemonServer {
+public:
+  SmallString<256> SocketPath;
+  SmallString<256> Stderr; // path to stderr
+  SmallString<256> Stdout; // path to stdout
+
+  explicit ModuleBuildDaemonServer(StringRef Path)
+      : SocketPath(Path), Stderr(Path), Stdout(Path) {
+    llvm::sys::path::append(SocketPath, SocketFileName);
+    llvm::sys::path::append(Stdout, StdoutFileName);
+    llvm::sys::path::append(Stderr, StderrFileName);
+  }
+
+  void setupDaemonEnv();
+  void createDaemonSocket();
+  void listenForClients();
+
+  static void handleConnection(std::shared_ptr<raw_socket_stream> Connection);
+
+  // TODO: modify so when shutdownDaemon is called the daemon stops accepting
+  // new client connections and waits for all existing client connections to
+  // terminate before closing the file descriptor and exiting
+  void shutdownDaemon() {
+    RunServiceLoop = false;
+    if (ServerListener.has_value())
+      ServerListener.value().shutdown();
+  }
+
+private:
+  std::atomic<bool> RunServiceLoop = true;
+  std::optional<llvm::ListeningSocket> ServerListener;
----------------
Bigcheese wrote:

This is set after the signal handler is installed so it needs to be atomic.
```suggestion
  std::atomic<llvm::ListeningSocket *> ServerListener;
  std::optional<llvm::ListeningSocket> ServerListenerStorage;
```

Then in `createDaemonSocket ` set `ServerListener = &*ServerListenerStorage`, and in `shutdownDaemon` use the `ServerListener` atomic pointer instead of the optional.

In the case that shutdown is called before the `ServerListener` is set, the server will still shutdown because `RunServiceLoop` will be false and `accept` will never be called.

https://github.com/llvm/llvm-project/pull/67562