[lldb] Adding pipe support to lldb_private::MainLoopWindows. (#145621)

This updates MainLoopWindows to support events for reading from a pipe
(both anonymous and named pipes) as well as sockets.

This unifies both handle types using `WSAWaitForMultipleEvents` which
can listen to both sockets and handles for change events.

This should allow us to unify how we handle watching pipes/sockets on
Windows and Posix systems.

We can extend this in the future if we want to support watching other
types, like files or even other events like a process life time.

---------

Co-authored-by: Pavel Labath <pavel@labath.sk>

lldb/source/Host/common/File.cpp

@@ -274,7 +274,11 @@ int NativeFile::GetDescriptor() const {
 }
 
 IOObject::WaitableHandle NativeFile::GetWaitableHandle() {
+#ifdef _WIN32
+  return (HANDLE)_get_osfhandle(GetDescriptor());
+#else
   return GetDescriptor();
+#endif
 }
 
 FILE *NativeFile::GetStream() {

lldb/source/Host/common/JSONTransport.cpp

@@ -42,7 +42,7 @@ ReadFull(IOObject &descriptor, size_t length,
   if (timeout && timeout_supported) {
     SelectHelper sh;
     sh.SetTimeout(*timeout);
-    sh.FDSetRead(descriptor.GetWaitableHandle());
+    sh.FDSetRead((lldb::socket_t)descriptor.GetWaitableHandle());
     Status status = sh.Select();
     if (status.Fail()) {
       // Convert timeouts into a specific error.

lldb/source/Host/common/Socket.cpp

@@ -313,8 +313,7 @@ Socket::DecodeHostAndPort(llvm::StringRef host_and_port) {
 }
 
 IOObject::WaitableHandle Socket::GetWaitableHandle() {
-  // TODO: On Windows, use WSAEventSelect
-  return m_socket;
+  return (IOObject::WaitableHandle)m_socket;
 }
 
 Status Socket::Read(void *buf, size_t &num_bytes) {

lldb/source/Host/posix/ConnectionFileDescriptorPosix.cpp

@@ -276,7 +276,7 @@ size_t ConnectionFileDescriptor::Read(void *dst, size_t dst_len,
               "%p ConnectionFileDescriptor::Read()  fd = %" PRIu64
               ", dst = %p, dst_len = %" PRIu64 ") => %" PRIu64 ", error = %s",
               static_cast<void *>(this),
-              static_cast<uint64_t>(m_io_sp->GetWaitableHandle()),
+              static_cast<file_t>(m_io_sp->GetWaitableHandle()),
               static_cast<void *>(dst), static_cast<uint64_t>(dst_len),
               static_cast<uint64_t>(bytes_read), error.AsCString());
   }
@@ -380,7 +380,7 @@ size_t ConnectionFileDescriptor::Write(const void *src, size_t src_len,
               "%p ConnectionFileDescriptor::Write(fd = %" PRIu64
               ", src = %p, src_len = %" PRIu64 ") => %" PRIu64 " (error = %s)",
               static_cast<void *>(this),
-              static_cast<uint64_t>(m_io_sp->GetWaitableHandle()),
+              static_cast<file_t>(m_io_sp->GetWaitableHandle()),
               static_cast<const void *>(src), static_cast<uint64_t>(src_len),
               static_cast<uint64_t>(bytes_sent), error.AsCString());
   }
@@ -451,7 +451,8 @@ ConnectionFileDescriptor::BytesAvailable(const Timeout<std::micro> &timeout,
     if (timeout)
       select_helper.SetTimeout(*timeout);
 
-    select_helper.FDSetRead(handle);
+    // FIXME: Migrate to MainLoop.
+    select_helper.FDSetRead((lldb::socket_t)handle);
 #if defined(_WIN32)
     // select() won't accept pipes on Windows.  The entire Windows codepath
     // needs to be converted over to using WaitForMultipleObjects and event
@@ -493,7 +494,7 @@ ConnectionFileDescriptor::BytesAvailable(const Timeout<std::micro> &timeout,
           break; // Lets keep reading to until we timeout
         }
       } else {
-        if (select_helper.FDIsSetRead(handle))
+        if (select_helper.FDIsSetRead((lldb::socket_t)handle))
           return eConnectionStatusSuccess;
 
         if (select_helper.FDIsSetRead(pipe_fd)) {

lldb/source/Host/windows/MainLoopWindows.cpp

@@ -8,8 +8,11 @@
 
 #include "lldb/Host/windows/MainLoopWindows.h"
 #include "lldb/Host/Config.h"
+#include "lldb/Host/Socket.h"
 #include "lldb/Utility/Status.h"
 #include "llvm/Config/llvm-config.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/WindowsError.h"
 #include <algorithm>
 #include <cassert>
 #include <cerrno>
@@ -31,6 +34,122 @@ static DWORD ToTimeout(std::optional<MainLoopWindows::TimePoint> point) {
   return ceil<milliseconds>(dur).count();
 }
 
+namespace {
+
+class PipeEvent : public MainLoopWindows::IOEvent {
+public:
+  explicit PipeEvent(HANDLE handle)
+      : IOEvent((IOObject::WaitableHandle)CreateEventW(
+            NULL, /*bManualReset=*/FALSE,
+            /*bInitialState=*/FALSE, NULL)),
+        m_handle(handle), m_ready(CreateEventW(NULL, /*bManualReset=*/FALSE,
+                                               /*bInitialState=*/FALSE, NULL)) {
+    assert(m_event && m_ready);
+  }
+
+  ~PipeEvent() override {
+    if (m_monitor_thread.joinable()) {
+      m_stopped = true;
+      SetEvent(m_ready);
+      // Keep trying to cancel ReadFile() until the thread exits.
+      do {
+        CancelIoEx((HANDLE)m_handle, /*lpOverlapped=*/NULL);
+      } while (WaitForSingleObject(m_monitor_thread.native_handle(), 1) ==
+               WAIT_TIMEOUT);
+      m_monitor_thread.join();
+    }
+    CloseHandle((HANDLE)m_event);
+    CloseHandle(m_ready);
+  }
+
+  void WillPoll() override {
+    if (!m_monitor_thread.joinable())
+      m_monitor_thread = std::thread(&PipeEvent::Monitor, this);
+  }
+
+  void Disarm() override { SetEvent(m_ready); }
+
+  /// Monitors the handle performing a zero byte read to determine when data is
+  /// avaiable.
+  void Monitor() {
+    do {
+      char buf[1];
+      DWORD bytes_read = 0;
+      OVERLAPPED ov = {0};
+      // Block on a 0-byte read; this will only resume when data is
+      // available in the pipe. The pipe must be PIPE_WAIT or this thread
+      // will spin.
+      BOOL success =
+          ReadFile(m_handle, buf, /*nNumberOfBytesToRead=*/0, &bytes_read, &ov);
+      DWORD bytes_available = 0;
+      DWORD err = GetLastError();
+      if (!success && err == ERROR_IO_PENDING) {
+        success = GetOverlappedResult(m_handle, &ov, &bytes_read,
+                                      /*bWait=*/TRUE);
+        err = GetLastError();
+      }
+      if (success) {
+        success =
+            PeekNamedPipe(m_handle, NULL, 0, NULL, &bytes_available, NULL);
+        err = GetLastError();
+      }
+      if (success) {
+        if (bytes_available == 0) {
+          // This can happen with a zero-byte write. Try again.
+          continue;
+        }
+      } else if (err == ERROR_NO_DATA) {
+        // The pipe is nonblocking. Try again.
+        Sleep(0);
+        continue;
+      } else if (err == ERROR_OPERATION_ABORTED) {
+        // Read may have been cancelled, try again.
+        continue;
+      }
+
+      SetEvent((HANDLE)m_event);
+
+      // Wait until the current read is consumed before doing the next read.
+      WaitForSingleObject(m_ready, INFINITE);
+    } while (!m_stopped);
+  }
+
+private:
+  HANDLE m_handle;
+  HANDLE m_ready;
+  std::thread m_monitor_thread;
+  std::atomic<bool> m_stopped = false;
+};
+
+class SocketEvent : public MainLoopWindows::IOEvent {
+public:
+  explicit SocketEvent(SOCKET socket)
+      : IOEvent((IOObject::WaitableHandle)WSACreateEvent()), m_socket(socket) {
+    assert(event != WSA_INVALID_EVENT);
+  }
+
+  ~SocketEvent() override { WSACloseEvent((HANDLE)m_event); }
+
+  void WillPoll() {
+    int result = WSAEventSelect(m_socket, (HANDLE)m_event,
+                                FD_READ | FD_ACCEPT | FD_CLOSE);
+    assert(result == 0);
+    UNUSED_IF_ASSERT_DISABLED(result);
+  }
+
+  void DidPoll() {
+    int result = WSAEventSelect(m_socket, WSA_INVALID_EVENT, 0);
+    assert(result == 0);
+    UNUSED_IF_ASSERT_DISABLED(result);
+  }
+
+  void Disarm() override { WSAResetEvent((HANDLE)m_event); }
+
+  SOCKET m_socket;
+};
+
+} // namespace
+
 MainLoopWindows::MainLoopWindows() {
   m_interrupt_event = WSACreateEvent();
   assert(m_interrupt_event != WSA_INVALID_EVENT);
@@ -44,14 +163,11 @@ MainLoopWindows::~MainLoopWindows() {
 }
 
 llvm::Expected<size_t> MainLoopWindows::Poll() {
-  std::vector<WSAEVENT> events;
+  std::vector<HANDLE> events;
   events.reserve(m_read_fds.size() + 1);
-  for (auto &[fd, info] : m_read_fds) {
-    int result = WSAEventSelect(fd, info.event, FD_READ | FD_ACCEPT | FD_CLOSE);
-    assert(result == 0);
-    UNUSED_IF_ASSERT_DISABLED(result);
-
-    events.push_back(info.event);
+  for (auto &[_, fd_info] : m_read_fds) {
+    fd_info.event->WillPoll();
+    events.push_back((HANDLE)fd_info.event->GetHandle());
   }
   events.push_back(m_interrupt_event);
 
@@ -59,11 +175,8 @@ llvm::Expected<size_t> MainLoopWindows::Poll() {
       WSAWaitForMultipleEvents(events.size(), events.data(), FALSE,
                                ToTimeout(GetNextWakeupTime()), FALSE);
 
-  for (auto &fd : m_read_fds) {
-    int result = WSAEventSelect(fd.first, WSA_INVALID_EVENT, 0);
-    assert(result == 0);
-    UNUSED_IF_ASSERT_DISABLED(result);
-  }
+  for (auto &[_, fd_info] : m_read_fds)
+    fd_info.event->DidPoll();
 
   if (result >= WSA_WAIT_EVENT_0 && result < WSA_WAIT_EVENT_0 + events.size())
     return result - WSA_WAIT_EVENT_0;
@@ -83,28 +196,25 @@ MainLoopWindows::RegisterReadObject(const IOObjectSP &object_sp,
     error = Status::FromErrorString("IO object is not valid.");
     return nullptr;
   }
-  if (object_sp->GetFdType() != IOObject::eFDTypeSocket) {
-    error = Status::FromErrorString(
-        "MainLoopWindows: non-socket types unsupported on Windows");
-    return nullptr;
-  }
 
-  WSAEVENT event = WSACreateEvent();
-  if (event == WSA_INVALID_EVENT) {
-    error =
-        Status::FromErrorStringWithFormat("Cannot create monitoring event.");
-    return nullptr;
-  }
+  IOObject::WaitableHandle waitable_handle = object_sp->GetWaitableHandle();
+  assert(waitable_handle != IOObject::kInvalidHandleValue);
 
-  const bool inserted =
-      m_read_fds
-          .try_emplace(object_sp->GetWaitableHandle(), FdInfo{event, callback})
-          .second;
-  if (!inserted) {
-    WSACloseEvent(event);
+  if (m_read_fds.find(waitable_handle) != m_read_fds.end()) {
     error = Status::FromErrorStringWithFormat(
-        "File descriptor %d already monitored.",
-        object_sp->GetWaitableHandle());
+        "File descriptor %d already monitored.", waitable_handle);
+    return nullptr;
+  }
+
+  if (object_sp->GetFdType() == IOObject::eFDTypeSocket)
+    m_read_fds[waitable_handle] = {
+        std::make_unique<SocketEvent>((SOCKET)waitable_handle), callback};
+  else if (GetFileType(waitable_handle) == FILE_TYPE_PIPE)
+    m_read_fds[waitable_handle] = {
+        std::make_unique<PipeEvent>((HANDLE)waitable_handle), callback};
+  else {
+    error = Status::FromErrorStringWithFormat("Unsupported file type %d",
+                                              GetFileType(waitable_handle));
     return nullptr;
   }
 
@@ -114,18 +224,9 @@ MainLoopWindows::RegisterReadObject(const IOObjectSP &object_sp,
 void MainLoopWindows::UnregisterReadObject(IOObject::WaitableHandle handle) {
   auto it = m_read_fds.find(handle);
   assert(it != m_read_fds.end());
-  BOOL result = WSACloseEvent(it->second.event);
-  assert(result == TRUE);
-  UNUSED_IF_ASSERT_DISABLED(result);
   m_read_fds.erase(it);
 }
 
-void MainLoopWindows::ProcessReadObject(IOObject::WaitableHandle handle) {
-  auto it = m_read_fds.find(handle);
-  if (it != m_read_fds.end())
-    it->second.callback(*this); // Do the work
-}
-
 Status MainLoopWindows::Run() {
   m_terminate_request = false;
 
@@ -138,8 +239,8 @@ Status MainLoopWindows::Run() {
 
     if (*signaled_event < m_read_fds.size()) {
       auto &KV = *std::next(m_read_fds.begin(), *signaled_event);
-      WSAResetEvent(KV.second.event);
-      ProcessReadObject(KV.first);
+      KV.second.event->Disarm();
+      KV.second.callback(*this); // Do the work.
     } else {
       assert(*signaled_event == m_read_fds.size());
       WSAResetEvent(m_interrupt_event);

lldb/source/Utility/IOObject.cpp

@@ -8,7 +8,16 @@
 
 #include "lldb/Utility/IOObject.h"
 
+#ifdef _WIN32
+#include "lldb/Host/windows/windows.h"
+#endif
+
 using namespace lldb_private;
 
+#ifdef _WIN32
+const IOObject::WaitableHandle IOObject::kInvalidHandleValue =
+    INVALID_HANDLE_VALUE;
+#else
 const IOObject::WaitableHandle IOObject::kInvalidHandleValue = -1;
+#endif
 IOObject::~IOObject() = default;