1 files changed, 408 insertions, 0 deletions
diff --git a/lldb/source/Host/common/MainLoop.cpp b/lldb/source/Host/common/MainLoop.cpp
new file mode 100644
index 000000000000..6f774451c8a4
--- /dev/null
+++ b/lldb/source/Host/common/MainLoop.cpp
@@ -0,0 +1,408 @@
+//===-- MainLoop.cpp --------------------------------------------*- 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 "llvm/Config/llvm-config.h"
+
+#include "lldb/Host/MainLoop.h"
+#include "lldb/Host/PosixApi.h"
+#include "lldb/Utility/Status.h"
+#include <algorithm>
+#include <cassert>
+#include <cerrno>
+#include <csignal>
+#include <time.h>
+#include <vector>
+
+// Multiplexing is implemented using kqueue on systems that support it (BSD
+// variants including OSX). On linux we use ppoll, while android uses pselect
+// (ppoll is present but not implemented properly). On windows we use WSApoll
+// (which does not support signals).
+
+#if HAVE_SYS_EVENT_H
+#include <sys/event.h>
+#elif defined(_WIN32)
+#include <winsock2.h>
+#elif defined(__ANDROID__)
+#include <sys/syscall.h>
+#else
+#include <poll.h>
+#endif
+
+#ifdef _WIN32
+#define POLL WSAPoll
+#else
+#define POLL poll
+#endif
+
+#if SIGNAL_POLLING_UNSUPPORTED
+#ifdef _WIN32
+typedef int sigset_t;
+typedef int siginfo_t;
+#endif
+
+int ppoll(struct pollfd *fds, size_t nfds, const struct timespec *timeout_ts,
+          const sigset_t *) {
+  int timeout =
+      (timeout_ts == nullptr)
+          ? -1
+          : (timeout_ts->tv_sec * 1000 + timeout_ts->tv_nsec / 1000000);
+  return POLL(fds, nfds, timeout);
+}
+
+#endif
+
+using namespace lldb;
+using namespace lldb_private;
+
+static sig_atomic_t g_signal_flags[NSIG];
+
+#ifndef SIGNAL_POLLING_UNSUPPORTED
+static void SignalHandler(int signo, siginfo_t *info, void *) {
+  assert(signo < NSIG);
+  g_signal_flags[signo] = 1;
+}
+#endif
+
+class MainLoop::RunImpl {
+public:
+  RunImpl(MainLoop &loop);
+  ~RunImpl() = default;
+
+  Status Poll();
+  void ProcessEvents();
+
+private:
+  MainLoop &loop;
+
+#if HAVE_SYS_EVENT_H
+  std::vector<struct kevent> in_events;
+  struct kevent out_events[4];
+  int num_events = -1;
+
+#else
+#ifdef __ANDROID__
+  fd_set read_fd_set;
+#else
+  std::vector<struct pollfd> read_fds;
+#endif
+
+  sigset_t get_sigmask();
+#endif
+};
+
+#if HAVE_SYS_EVENT_H
+MainLoop::RunImpl::RunImpl(MainLoop &loop) : loop(loop) {
+  in_events.reserve(loop.m_read_fds.size());
+}
+
+Status MainLoop::RunImpl::Poll() {
+  in_events.resize(loop.m_read_fds.size());
+  unsigned i = 0;
+  for (auto &fd : loop.m_read_fds)
+    EV_SET(&in_events[i++], fd.first, EVFILT_READ, EV_ADD, 0, 0, 0);
+
+  num_events = kevent(loop.m_kqueue, in_events.data(), in_events.size(),
+                      out_events, llvm::array_lengthof(out_events), nullptr);
+
+  if (num_events < 0) {
+    if (errno == EINTR) {
+      // in case of EINTR, let the main loop run one iteration
+      // we need to zero num_events to avoid assertions failing
+      num_events = 0;
+    } else
+      return Status(errno, eErrorTypePOSIX);
+  }
+  return Status();
+}
+
+void MainLoop::RunImpl::ProcessEvents() {
+  assert(num_events >= 0);
+  for (int i = 0; i < num_events; ++i) {
+    if (loop.m_terminate_request)
+      return;
+    switch (out_events[i].filter) {
+    case EVFILT_READ:
+      loop.ProcessReadObject(out_events[i].ident);
+      break;
+    case EVFILT_SIGNAL:
+      loop.ProcessSignal(out_events[i].ident);
+      break;
+    default:
+      llvm_unreachable("Unknown event");
+    }
+  }
+}
+#else
+MainLoop::RunImpl::RunImpl(MainLoop &loop) : loop(loop) {
+#ifndef __ANDROID__
+  read_fds.reserve(loop.m_read_fds.size());
+#endif
+}
+
+sigset_t MainLoop::RunImpl::get_sigmask() {
+  sigset_t sigmask;
+#if defined(_WIN32)
+  sigmask = 0;
+#elif SIGNAL_POLLING_UNSUPPORTED
+  sigemptyset(&sigmask);
+#else
+  int ret = pthread_sigmask(SIG_SETMASK, nullptr, &sigmask);
+  assert(ret == 0);
+  (void) ret;
+
+  for (const auto &sig : loop.m_signals)
+    sigdelset(&sigmask, sig.first);
+#endif
+  return sigmask;
+}
+
+#ifdef __ANDROID__
+Status MainLoop::RunImpl::Poll() {
+  // ppoll(2) is not supported on older all android versions. Also, older
+  // versions android (API <= 19) implemented pselect in a non-atomic way, as a
+  // combination of pthread_sigmask and select. This is not sufficient for us,
+  // as we rely on the atomicity to correctly implement signal polling, so we
+  // call the underlying syscall ourselves.
+
+  FD_ZERO(&read_fd_set);
+  int nfds = 0;
+  for (const auto &fd : loop.m_read_fds) {
+    FD_SET(fd.first, &read_fd_set);
+    nfds = std::max(nfds, fd.first + 1);
+  }
+
+  union {
+    sigset_t set;
+    uint64_t pad;
+  } kernel_sigset;
+  memset(&kernel_sigset, 0, sizeof(kernel_sigset));
+  kernel_sigset.set = get_sigmask();
+
+  struct {
+    void *sigset_ptr;
+    size_t sigset_len;
+  } extra_data = {&kernel_sigset, sizeof(kernel_sigset)};
+  if (syscall(__NR_pselect6, nfds, &read_fd_set, nullptr, nullptr, nullptr,
+              &extra_data) == -1 &&
+      errno != EINTR)
+    return Status(errno, eErrorTypePOSIX);
+
+  return Status();
+}
+#else
+Status MainLoop::RunImpl::Poll() {
+  read_fds.clear();
+
+  sigset_t sigmask = get_sigmask();
+
+  for (const auto &fd : loop.m_read_fds) {
+    struct pollfd pfd;
+    pfd.fd = fd.first;
+    pfd.events = POLLIN;
+    pfd.revents = 0;
+    read_fds.push_back(pfd);
+  }
+
+  if (ppoll(read_fds.data(), read_fds.size(), nullptr, &sigmask) == -1 &&
+      errno != EINTR)
+    return Status(errno, eErrorTypePOSIX);
+
+  return Status();
+}
+#endif
+
+void MainLoop::RunImpl::ProcessEvents() {
+#ifdef __ANDROID__
+  // Collect first all readable file descriptors into a separate vector and
+  // then iterate over it to invoke callbacks. Iterating directly over
+  // loop.m_read_fds is not possible because the callbacks can modify the
+  // container which could invalidate the iterator.
+  std::vector<IOObject::WaitableHandle> fds;
+  for (const auto &fd : loop.m_read_fds)
+    if (FD_ISSET(fd.first, &read_fd_set))
+      fds.push_back(fd.first);
+
+  for (const auto &handle : fds) {
+#else
+  for (const auto &fd : read_fds) {
+    if ((fd.revents & (POLLIN | POLLHUP)) == 0)
+      continue;
+    IOObject::WaitableHandle handle = fd.fd;
+#endif
+    if (loop.m_terminate_request)
+      return;
+
+    loop.ProcessReadObject(handle);
+  }
+
+  std::vector<int> signals;
+  for (const auto &entry : loop.m_signals)
+    if (g_signal_flags[entry.first] != 0)
+      signals.push_back(entry.first);
+
+  for (const auto &signal : signals) {
+    if (loop.m_terminate_request)
+      return;
+    g_signal_flags[signal] = 0;
+    loop.ProcessSignal(signal);
+  }
+}
+#endif
+
+MainLoop::MainLoop() {
+#if HAVE_SYS_EVENT_H
+  m_kqueue = kqueue();
+  assert(m_kqueue >= 0);
+#endif
+}
+MainLoop::~MainLoop() {
+#if HAVE_SYS_EVENT_H
+  close(m_kqueue);
+#endif
+  assert(m_read_fds.size() == 0);
+  assert(m_signals.size() == 0);
+}
+
+MainLoop::ReadHandleUP MainLoop::RegisterReadObject(const IOObjectSP &object_sp,
+                                                    const Callback &callback,
+                                                    Status &error) {
+#ifdef _WIN32
+  if (object_sp->GetFdType() != IOObject:: eFDTypeSocket) {
+    error.SetErrorString("MainLoop: non-socket types unsupported on Windows");
+    return nullptr;
+  }
+#endif
+  if (!object_sp || !object_sp->IsValid()) {
+    error.SetErrorString("IO object is not valid.");
+    return nullptr;
+  }
+
+  const bool inserted =
+      m_read_fds.insert({object_sp->GetWaitableHandle(), callback}).second;
+  if (!inserted) {
+    error.SetErrorStringWithFormat("File descriptor %d already monitored.",
+                                   object_sp->GetWaitableHandle());
+    return nullptr;
+  }
+
+  return CreateReadHandle(object_sp);
+}
+
+// We shall block the signal, then install the signal handler. The signal will
+// be unblocked in the Run() function to check for signal delivery.
+MainLoop::SignalHandleUP
+MainLoop::RegisterSignal(int signo, const Callback &callback, Status &error) {
+#ifdef SIGNAL_POLLING_UNSUPPORTED
+  error.SetErrorString("Signal polling is not supported on this platform.");
+  return nullptr;
+#else
+  if (m_signals.find(signo) != m_signals.end()) {
+    error.SetErrorStringWithFormat("Signal %d already monitored.", signo);
+    return nullptr;
+  }
+
+  SignalInfo info;
+  info.callback = callback;
+  struct sigaction new_action;
+  new_action.sa_sigaction = &SignalHandler;
+  new_action.sa_flags = SA_SIGINFO;
+  sigemptyset(&new_action.sa_mask);
+  sigaddset(&new_action.sa_mask, signo);
+  sigset_t old_set;
+
+  g_signal_flags[signo] = 0;
+
+  // Even if using kqueue, the signal handler will still be invoked, so it's
+  // important to replace it with our "benign" handler.
+  int ret = sigaction(signo, &new_action, &info.old_action);
+  (void)ret;
+  assert(ret == 0 && "sigaction failed");
+
+#if HAVE_SYS_EVENT_H
+  struct kevent ev;
+  EV_SET(&ev, signo, EVFILT_SIGNAL, EV_ADD, 0, 0, 0);
+  ret = kevent(m_kqueue, &ev, 1, nullptr, 0, nullptr);
+  assert(ret == 0);
+#endif
+
+  // If we're using kqueue, the signal needs to be unblocked in order to
+  // receive it. If using pselect/ppoll, we need to block it, and later unblock
+  // it as a part of the system call.
+  ret = pthread_sigmask(HAVE_SYS_EVENT_H ? SIG_UNBLOCK : SIG_BLOCK,
+                        &new_action.sa_mask, &old_set);
+  assert(ret == 0 && "pthread_sigmask failed");
+  info.was_blocked = sigismember(&old_set, signo);
+  m_signals.insert({signo, info});
+
+  return SignalHandleUP(new SignalHandle(*this, signo));
+#endif
+}
+
+void MainLoop::UnregisterReadObject(IOObject::WaitableHandle handle) {
+  bool erased = m_read_fds.erase(handle);
+  UNUSED_IF_ASSERT_DISABLED(erased);
+  assert(erased);
+}
+
+void MainLoop::UnregisterSignal(int signo) {
+#if SIGNAL_POLLING_UNSUPPORTED
+  Status("Signal polling is not supported on this platform.");
+#else
+  auto it = m_signals.find(signo);
+  assert(it != m_signals.end());
+
+  sigaction(signo, &it->second.old_action, nullptr);
+
+  sigset_t set;
+  sigemptyset(&set);
+  sigaddset(&set, signo);
+  int ret = pthread_sigmask(it->second.was_blocked ? SIG_BLOCK : SIG_UNBLOCK,
+                            &set, nullptr);
+  assert(ret == 0);
+  (void)ret;
+
+#if HAVE_SYS_EVENT_H
+  struct kevent ev;
+  EV_SET(&ev, signo, EVFILT_SIGNAL, EV_DELETE, 0, 0, 0);
+  ret = kevent(m_kqueue, &ev, 1, nullptr, 0, nullptr);
+  assert(ret == 0);
+#endif
+
+  m_signals.erase(it);
+#endif
+}
+
+Status MainLoop::Run() {
+  m_terminate_request = false;
+
+  Status error;
+  RunImpl impl(*this);
+
+  // run until termination or until we run out of things to listen to
+  while (!m_terminate_request && (!m_read_fds.empty() || !m_signals.empty())) {
+
+    error = impl.Poll();
+    if (error.Fail())
+      return error;
+
+    impl.ProcessEvents();
+  }
+  return Status();
+}
+
+void MainLoop::ProcessSignal(int signo) {
+  auto it = m_signals.find(signo);
+  if (it != m_signals.end())
+    it->second.callback(*this); // Do the work
+}
+
+void MainLoop::ProcessReadObject(IOObject::WaitableHandle handle) {
+  auto it = m_read_fds.find(handle);
+  if (it != m_read_fds.end())
+    it->second(*this); // Do the work
+}