DirectoryWatcher: add an implementation for Windows

This implements the directory watcher on Windows.  It does the most
naive thing for simplicity.  ReadDirectoryChangesW is used to monitor
the changes.  However, in order to support interruption, we must use
overlapped IO, which allows us to use the blocking, synchronous
mechanism.  We create a thread to post the notification to the consumer
to allow the monitoring to continue.  The two threads communicate via a
locked queue.

Differential Revision: https://reviews.llvm.org/D88666
Reviewed By: Adrian McCarthy

clang/lib/DirectoryWatcher/windows/DirectoryWatcher-windows.cpp

@@ -6,19 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-// TODO: This is not yet an implementation, but it will make it so Windows
-//       builds don't fail.
-
 #include "DirectoryScanner.h"
 #include "clang/DirectoryWatcher/DirectoryWatcher.h"
-
 #include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/ScopeExit.h"
-#include "llvm/Support/AlignOf.h"
-#include "llvm/Support/Errno.h"
-#include "llvm/Support/Mutex.h"
+#include "llvm/Support/ConvertUTF.h"
 #include "llvm/Support/Path.h"
-#include <atomic>
+#include "llvm/Support/Windows/WindowsSupport.h"
 #include <condition_variable>
 #include <mutex>
 #include <queue>
@@ -28,23 +21,270 @@
 
 namespace {
 
+using DirectoryWatcherCallback =
+    std::function<void(llvm::ArrayRef<clang::DirectoryWatcher::Event>, bool)>;
+
 using namespace llvm;
 using namespace clang;
 
 class DirectoryWatcherWindows : public clang::DirectoryWatcher {
+  OVERLAPPED Overlapped;
+
+  std::vector<DWORD> Notifications;
+
+  std::thread WatcherThread;
+  std::thread HandlerThread;
+  std::function<void(ArrayRef<DirectoryWatcher::Event>, bool)> Callback;
+  SmallString<MAX_PATH> Path;
+  HANDLE Terminate;
+
+  class EventQueue {
+    std::mutex M;
+    std::queue<DirectoryWatcher::Event> Q;
+    std::condition_variable CV;
+
+  public:
+    void emplace(DirectoryWatcher::Event::EventKind Kind, StringRef Path) {
+      {
+        std::unique_lock<std::mutex> L(M);
+        Q.emplace(Kind, Path);
+      }
+      CV.notify_one();
+    }
+
+    DirectoryWatcher::Event pop_front() {
+      std::unique_lock<std::mutex> L(M);
+      while (true) {
+        if (!Q.empty()) {
+          DirectoryWatcher::Event E = Q.front();
+          Q.pop();
+          return E;
+        }
+        CV.wait(L, [this]() { return !Q.empty(); });
+      }
+    }
+  } Q;
+
 public:
-  ~DirectoryWatcherWindows() override { }
-  void InitialScan() { }
-  void EventReceivingLoop() { }
-  void StopWork() { }
+  DirectoryWatcherWindows(HANDLE DirectoryHandle, bool WaitForInitialSync,
+                          DirectoryWatcherCallback Receiver);
+
+  ~DirectoryWatcherWindows() override;
+
+  void InitialScan();
+  void WatcherThreadProc(HANDLE DirectoryHandle);
+  void NotifierThreadProc(bool WaitForInitialSync);
 };
+
+DirectoryWatcherWindows::DirectoryWatcherWindows(
+    HANDLE DirectoryHandle, bool WaitForInitialSync,
+    DirectoryWatcherCallback Receiver)
+    : Callback(Receiver), Terminate(INVALID_HANDLE_VALUE) {
+  // Pre-compute the real location as we will be handing over the directory
+  // handle to the watcher and performing synchronous operations.
+  {
+    DWORD Length = GetFinalPathNameByHandleW(DirectoryHandle, NULL, 0, 0);
+
+    std::vector<WCHAR> Buffer;
+    Buffer.resize(Length);
+
+    Length = GetFinalPathNameByHandleW(DirectoryHandle, Buffer.data(),
+                                       Buffer.size(), 0);
+    Buffer.resize(Length);
+
+    llvm::sys::windows::UTF16ToUTF8(Buffer.data(), Buffer.size(), Path);
+  }
+
+  Notifications.resize(4 * (sizeof(FILE_NOTIFY_INFORMATION) +
+                            MAX_PATH * sizeof(WCHAR)));
+
+  memset(&Overlapped, 0, sizeof(Overlapped));
+  Overlapped.hEvent =
+      CreateEventW(NULL, /*bManualReset=*/TRUE, /*bInitialState=*/FALSE, NULL);
+  assert(Overlapped.hEvent && "unable to create event");
+
+  Terminate = CreateEventW(NULL, /*bManualReset=*/TRUE,
+                           /*bInitialState=*/FALSE, NULL);
+
+  WatcherThread = std::thread([this, DirectoryHandle]() {
+    this->WatcherThreadProc(DirectoryHandle);
+  });
+
+  if (WaitForInitialSync)
+    InitialScan();
+
+  HandlerThread = std::thread([this, WaitForInitialSync]() {
+    this->NotifierThreadProc(WaitForInitialSync);
+  });
+}
+
+DirectoryWatcherWindows::~DirectoryWatcherWindows() {
+  // Signal the Watcher to exit.
+  SetEvent(Terminate);
+  HandlerThread.join();
+  WatcherThread.join();
+  CloseHandle(Terminate);
+  CloseHandle(Overlapped.hEvent);
+}
+
+void DirectoryWatcherWindows::InitialScan() {
+  Callback(getAsFileEvents(scanDirectory(Path.data())), /*IsInitial=*/true);
+}
+
+void DirectoryWatcherWindows::WatcherThreadProc(HANDLE DirectoryHandle) {
+  while (true) {
+    // We do not guarantee subdirectories, but macOS already provides
+    // subdirectories, might as well as ...
+    BOOL WatchSubtree = TRUE;
+    DWORD NotifyFilter = FILE_NOTIFY_CHANGE_FILE_NAME
+                       | FILE_NOTIFY_CHANGE_DIR_NAME
+                       | FILE_NOTIFY_CHANGE_SIZE
+                       | FILE_NOTIFY_CHANGE_LAST_ACCESS
+                       | FILE_NOTIFY_CHANGE_LAST_WRITE
+                       | FILE_NOTIFY_CHANGE_CREATION;
+
+    DWORD BytesTransferred;
+    if (!ReadDirectoryChangesW(DirectoryHandle, Notifications.data(),
+                               Notifications.size(), WatchSubtree,
+                               NotifyFilter, &BytesTransferred, &Overlapped,
+                               NULL)) {
+      Q.emplace(DirectoryWatcher::Event::EventKind::WatcherGotInvalidated,
+                "");
+      break;
+    }
+
+    HANDLE Handles[2] = { Terminate, Overlapped.hEvent };
+    switch (WaitForMultipleObjects(2, Handles, FALSE, INFINITE)) {
+    case WAIT_OBJECT_0: // Terminate Request
+    case WAIT_FAILED:   // Failure
+      Q.emplace(DirectoryWatcher::Event::EventKind::WatcherGotInvalidated,
+                "");
+      (void)CloseHandle(DirectoryHandle);
+      return;
+    case WAIT_TIMEOUT:  // Spurious wakeup?
+      continue;
+    case WAIT_OBJECT_0 + 1: // Directory change
+      break;
+    }
+
+    if (!GetOverlappedResult(DirectoryHandle, &Overlapped, &BytesTransferred,
+                             FALSE)) {
+      Q.emplace(DirectoryWatcher::Event::EventKind::WatchedDirRemoved,
+                "");
+      Q.emplace(DirectoryWatcher::Event::EventKind::WatcherGotInvalidated,
+                "");
+      break;
+    }
+
+    // There was a buffer underrun on the kernel side.  We may have lost
+    // events, please re-synchronize.
+    if (BytesTransferred == 0) {
+      Q.emplace(DirectoryWatcher::Event::EventKind::WatcherGotInvalidated,
+                "");
+      break;
+    }
+
+    for (FILE_NOTIFY_INFORMATION *I =
+            (FILE_NOTIFY_INFORMATION *)Notifications.data();
+         I;
+         I = I->NextEntryOffset
+              ? (FILE_NOTIFY_INFORMATION *)((CHAR *)I + I->NextEntryOffset)
+              : NULL) {
+      DirectoryWatcher::Event::EventKind Kind =
+          DirectoryWatcher::Event::EventKind::WatcherGotInvalidated;
+      switch (I->Action) {
+      case FILE_ACTION_MODIFIED:
+        Kind = DirectoryWatcher::Event::EventKind::Modified;
+        break;
+      case FILE_ACTION_ADDED:
+        Kind = DirectoryWatcher::Event::EventKind::Modified;
+        break;
+      case FILE_ACTION_REMOVED:
+        Kind = DirectoryWatcher::Event::EventKind::Removed;
+        break;
+      case FILE_ACTION_RENAMED_OLD_NAME:
+        Kind = DirectoryWatcher::Event::EventKind::Removed;
+        break;
+      case FILE_ACTION_RENAMED_NEW_NAME:
+        Kind = DirectoryWatcher::Event::EventKind::Modified;
+        break;
+      }
+
+      SmallString<MAX_PATH> filename;
+      sys::windows::UTF16ToUTF8(I->FileName, I->FileNameLength / 2,
+                                filename);
+      Q.emplace(Kind, filename);
+    }
+  }
+
+  (void)CloseHandle(DirectoryHandle);
+}
+
+void DirectoryWatcherWindows::NotifierThreadProc(bool WaitForInitialSync) {
+  // If we did not wait for the initial sync, then we should perform the
+  // scan when we enter the thread.
+  if (!WaitForInitialSync)
+    this->InitialScan();
+
+  while (true) {
+    DirectoryWatcher::Event E = Q.pop_front();
+    Callback(E, /*IsInitial=*/false);
+    if (E.Kind == DirectoryWatcher::Event::EventKind::WatcherGotInvalidated)
+      break;
+  }
+}
+
+auto error(DWORD ErrorCode) {
+  DWORD Flags = FORMAT_MESSAGE_ALLOCATE_BUFFER
+              | FORMAT_MESSAGE_FROM_SYSTEM
+              | FORMAT_MESSAGE_IGNORE_INSERTS;
+
+  LPSTR Buffer;
+  if (!FormatMessageA(Flags, NULL, ErrorCode,
+                      MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPSTR)&Buffer,
+                      0, NULL)) {
+    return make_error<llvm::StringError>("error " + utostr(ErrorCode),
+                                         inconvertibleErrorCode());
+  }
+  std::string Message{Buffer};
+  LocalFree(Buffer);
+  return make_error<llvm::StringError>(Message, inconvertibleErrorCode());
+}
+
 } // namespace
 
 llvm::Expected<std::unique_ptr<DirectoryWatcher>>
-clang::DirectoryWatcher::create(
-    StringRef Path,
-    std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)> Receiver,
-    bool WaitForInitialSync) {
-  return llvm::Expected<std::unique_ptr<DirectoryWatcher>>(
-      llvm::errorCodeToError(std::make_error_code(std::errc::not_supported)));
+clang::DirectoryWatcher::create(StringRef Path,
+                                DirectoryWatcherCallback Receiver,
+                                bool WaitForInitialSync) {
+  if (Path.empty())
+    llvm::report_fatal_error(
+        "DirectoryWatcher::create can not accept an empty Path.");
+
+  if (!sys::fs::is_directory(Path))
+    llvm::report_fatal_error(
+        "DirectoryWatcher::create can not accept a filepath.");
+
+  SmallVector<wchar_t, MAX_PATH> WidePath;
+  if (sys::windows::UTF8ToUTF16(Path, WidePath))
+    return llvm::make_error<llvm::StringError>(
+        "unable to convert path to UTF-16", llvm::inconvertibleErrorCode());
+
+  DWORD DesiredAccess = FILE_LIST_DIRECTORY;
+  DWORD ShareMode = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
+  DWORD CreationDisposition = OPEN_EXISTING;
+  DWORD FlagsAndAttributes = FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED;
+
+  HANDLE DirectoryHandle =
+      CreateFileW(WidePath.data(), DesiredAccess, ShareMode,
+                  /*lpSecurityAttributes=*/NULL, CreationDisposition,
+                  FlagsAndAttributes, NULL);
+  if (DirectoryHandle == INVALID_HANDLE_VALUE)
+    return error(GetLastError());
+
+  // NOTE: We use the watcher instance as a RAII object to discard the handles
+  // for the directory and the IOCP in case of an error.  Hence, this is early
+  // allocated, with the state being written directly to the watcher.
+  return std::make_unique<DirectoryWatcherWindows>(
+      DirectoryHandle, WaitForInitialSync, Receiver);
 }

clang/unittests/DirectoryWatcher/CMakeLists.txt

@@ -1,4 +1,4 @@
-if(APPLE OR CMAKE_SYSTEM_NAME MATCHES "Linux")
+if(APPLE OR CMAKE_SYSTEM_NAME MATCHES "Linux" OR CMAKE_SYSTEM_NAME STREQUAL Windows)
 
   set(LLVM_LINK_COMPONENTS
     Support