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MainLoop.cpp
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1 //===-- MainLoop.cpp ------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "llvm/Config/llvm-config.h"
10 #include "lldb/Host/Config.h"
11 
12 #include "lldb/Host/MainLoop.h"
13 #include "lldb/Host/PosixApi.h"
14 #include "lldb/Utility/Status.h"
15 #include <algorithm>
16 #include <cassert>
17 #include <cerrno>
18 #include <csignal>
19 #include <time.h>
20 #include <vector>
21 
22 // Multiplexing is implemented using kqueue on systems that support it (BSD
23 // variants including OSX). On linux we use ppoll, while android uses pselect
24 // (ppoll is present but not implemented properly). On windows we use WSApoll
25 // (which does not support signals).
26 
27 #if HAVE_SYS_EVENT_H
28 #include <sys/event.h>
29 #elif defined(_WIN32)
30 #include <winsock2.h>
31 #elif defined(__ANDROID__)
32 #include <sys/syscall.h>
33 #else
34 #include <poll.h>
35 #endif
36 
37 #ifdef _WIN32
38 #define POLL WSAPoll
39 #else
40 #define POLL poll
41 #endif
42 
43 #if SIGNAL_POLLING_UNSUPPORTED
44 #ifdef _WIN32
45 typedef int sigset_t;
46 typedef int siginfo_t;
47 #endif
48 
49 int ppoll(struct pollfd *fds, size_t nfds, const struct timespec *timeout_ts,
50  const sigset_t *) {
51  int timeout =
52  (timeout_ts == nullptr)
53  ? -1
54  : (timeout_ts->tv_sec * 1000 + timeout_ts->tv_nsec / 1000000);
55  return POLL(fds, nfds, timeout);
56 }
57 
58 #endif
59 
60 using namespace lldb;
61 using namespace lldb_private;
62 
63 static sig_atomic_t g_signal_flags[NSIG];
64 
65 #ifndef SIGNAL_POLLING_UNSUPPORTED
66 static void SignalHandler(int signo, siginfo_t *info, void *) {
67  assert(signo < NSIG);
68  g_signal_flags[signo] = 1;
69 }
70 #endif
71 
73 public:
74  RunImpl(MainLoop &loop);
75  ~RunImpl() = default;
76 
77  Status Poll();
78  void ProcessEvents();
79 
80 private:
82 
83 #if HAVE_SYS_EVENT_H
84  std::vector<struct kevent> in_events;
85  struct kevent out_events[4];
86  int num_events = -1;
87 
88 #else
89 #ifdef __ANDROID__
90  fd_set read_fd_set;
91 #else
92  std::vector<struct pollfd> read_fds;
93 #endif
94 
95  sigset_t get_sigmask();
96 #endif
97 };
98 
99 #if HAVE_SYS_EVENT_H
100 MainLoop::RunImpl::RunImpl(MainLoop &loop) : loop(loop) {
101  in_events.reserve(loop.m_read_fds.size());
102 }
103 
105  in_events.resize(loop.m_read_fds.size());
106  unsigned i = 0;
107  for (auto &fd : loop.m_read_fds)
108  EV_SET(&in_events[i++], fd.first, EVFILT_READ, EV_ADD, 0, 0, 0);
109 
110  num_events = kevent(loop.m_kqueue, in_events.data(), in_events.size(),
111  out_events, llvm::array_lengthof(out_events), nullptr);
112 
113  if (num_events < 0) {
114  if (errno == EINTR) {
115  // in case of EINTR, let the main loop run one iteration
116  // we need to zero num_events to avoid assertions failing
117  num_events = 0;
118  } else
119  return Status(errno, eErrorTypePOSIX);
120  }
121  return Status();
122 }
123 
125  assert(num_events >= 0);
126  for (int i = 0; i < num_events; ++i) {
127  if (loop.m_terminate_request)
128  return;
129  switch (out_events[i].filter) {
130  case EVFILT_READ:
131  loop.ProcessReadObject(out_events[i].ident);
132  break;
133  case EVFILT_SIGNAL:
134  loop.ProcessSignal(out_events[i].ident);
135  break;
136  default:
137  llvm_unreachable("Unknown event");
138  }
139  }
140 }
141 #else
143 #ifndef __ANDROID__
144  read_fds.reserve(loop.m_read_fds.size());
145 #endif
146 }
147 
149  sigset_t sigmask;
150 #if defined(_WIN32)
151  sigmask = 0;
152 #elif SIGNAL_POLLING_UNSUPPORTED
153  sigemptyset(&sigmask);
154 #else
155  int ret = pthread_sigmask(SIG_SETMASK, nullptr, &sigmask);
156  assert(ret == 0);
157  (void) ret;
158 
159  for (const auto &sig : loop.m_signals)
160  sigdelset(&sigmask, sig.first);
161 #endif
162  return sigmask;
163 }
164 
165 #ifdef __ANDROID__
167  // ppoll(2) is not supported on older all android versions. Also, older
168  // versions android (API <= 19) implemented pselect in a non-atomic way, as a
169  // combination of pthread_sigmask and select. This is not sufficient for us,
170  // as we rely on the atomicity to correctly implement signal polling, so we
171  // call the underlying syscall ourselves.
172 
173  FD_ZERO(&read_fd_set);
174  int nfds = 0;
175  for (const auto &fd : loop.m_read_fds) {
176  FD_SET(fd.first, &read_fd_set);
177  nfds = std::max(nfds, fd.first + 1);
178  }
179 
180  union {
181  sigset_t set;
182  uint64_t pad;
183  } kernel_sigset;
184  memset(&kernel_sigset, 0, sizeof(kernel_sigset));
185  kernel_sigset.set = get_sigmask();
186 
187  struct {
188  void *sigset_ptr;
189  size_t sigset_len;
190  } extra_data = {&kernel_sigset, sizeof(kernel_sigset)};
191  if (syscall(__NR_pselect6, nfds, &read_fd_set, nullptr, nullptr, nullptr,
192  &extra_data) == -1 &&
193  errno != EINTR)
194  return Status(errno, eErrorTypePOSIX);
195 
196  return Status();
197 }
198 #else
200  read_fds.clear();
201 
202  sigset_t sigmask = get_sigmask();
203 
204  for (const auto &fd : loop.m_read_fds) {
205  struct pollfd pfd;
206  pfd.fd = fd.first;
207  pfd.events = POLLIN;
208  pfd.revents = 0;
209  read_fds.push_back(pfd);
210  }
211 
212  if (ppoll(read_fds.data(), read_fds.size(), nullptr, &sigmask) == -1 &&
213  errno != EINTR)
214  return Status(errno, eErrorTypePOSIX);
215 
216  return Status();
217 }
218 #endif
219 
221 #ifdef __ANDROID__
222  // Collect first all readable file descriptors into a separate vector and
223  // then iterate over it to invoke callbacks. Iterating directly over
224  // loop.m_read_fds is not possible because the callbacks can modify the
225  // container which could invalidate the iterator.
226  std::vector<IOObject::WaitableHandle> fds;
227  for (const auto &fd : loop.m_read_fds)
228  if (FD_ISSET(fd.first, &read_fd_set))
229  fds.push_back(fd.first);
230 
231  for (const auto &handle : fds) {
232 #else
233  for (const auto &fd : read_fds) {
234  if ((fd.revents & (POLLIN | POLLHUP)) == 0)
235  continue;
236  IOObject::WaitableHandle handle = fd.fd;
237 #endif
238  if (loop.m_terminate_request)
239  return;
240 
241  loop.ProcessReadObject(handle);
242  }
243 
244  std::vector<int> signals;
245  for (const auto &entry : loop.m_signals)
246  if (g_signal_flags[entry.first] != 0)
247  signals.push_back(entry.first);
248 
249  for (const auto &signal : signals) {
250  if (loop.m_terminate_request)
251  return;
252  g_signal_flags[signal] = 0;
253  loop.ProcessSignal(signal);
254  }
255 }
256 #endif
257 
258 MainLoop::MainLoop() {
259 #if HAVE_SYS_EVENT_H
260  m_kqueue = kqueue();
261  assert(m_kqueue >= 0);
262 #endif
263 }
264 MainLoop::~MainLoop() {
265 #if HAVE_SYS_EVENT_H
266  close(m_kqueue);
267 #endif
268  assert(m_read_fds.size() == 0);
269  assert(m_signals.size() == 0);
270 }
271 
272 MainLoop::ReadHandleUP MainLoop::RegisterReadObject(const IOObjectSP &object_sp,
273  const Callback &callback,
274  Status &error) {
275 #ifdef _WIN32
276  if (object_sp->GetFdType() != IOObject:: eFDTypeSocket) {
277  error.SetErrorString("MainLoop: non-socket types unsupported on Windows");
278  return nullptr;
279  }
280 #endif
281  if (!object_sp || !object_sp->IsValid()) {
282  error.SetErrorString("IO object is not valid.");
283  return nullptr;
284  }
285 
286  const bool inserted =
287  m_read_fds.insert({object_sp->GetWaitableHandle(), callback}).second;
288  if (!inserted) {
289  error.SetErrorStringWithFormat("File descriptor %d already monitored.",
290  object_sp->GetWaitableHandle());
291  return nullptr;
292  }
293 
294  return CreateReadHandle(object_sp);
295 }
296 
297 // We shall block the signal, then install the signal handler. The signal will
298 // be unblocked in the Run() function to check for signal delivery.
300 MainLoop::RegisterSignal(int signo, const Callback &callback, Status &error) {
301 #ifdef SIGNAL_POLLING_UNSUPPORTED
302  error.SetErrorString("Signal polling is not supported on this platform.");
303  return nullptr;
304 #else
305  if (m_signals.find(signo) != m_signals.end()) {
306  error.SetErrorStringWithFormat("Signal %d already monitored.", signo);
307  return nullptr;
308  }
309 
310  SignalInfo info;
311  info.callback = callback;
312  struct sigaction new_action;
313  new_action.sa_sigaction = &SignalHandler;
314  new_action.sa_flags = SA_SIGINFO;
315  sigemptyset(&new_action.sa_mask);
316  sigaddset(&new_action.sa_mask, signo);
317  sigset_t old_set;
318 
319  g_signal_flags[signo] = 0;
320 
321  // Even if using kqueue, the signal handler will still be invoked, so it's
322  // important to replace it with our "benign" handler.
323  int ret = sigaction(signo, &new_action, &info.old_action);
324  (void)ret;
325  assert(ret == 0 && "sigaction failed");
326 
327 #if HAVE_SYS_EVENT_H
328  struct kevent ev;
329  EV_SET(&ev, signo, EVFILT_SIGNAL, EV_ADD, 0, 0, 0);
330  ret = kevent(m_kqueue, &ev, 1, nullptr, 0, nullptr);
331  assert(ret == 0);
332 #endif
333 
334  // If we're using kqueue, the signal needs to be unblocked in order to
335  // receive it. If using pselect/ppoll, we need to block it, and later unblock
336  // it as a part of the system call.
337  ret = pthread_sigmask(HAVE_SYS_EVENT_H ? SIG_UNBLOCK : SIG_BLOCK,
338  &new_action.sa_mask, &old_set);
339  assert(ret == 0 && "pthread_sigmask failed");
340  info.was_blocked = sigismember(&old_set, signo);
341  m_signals.insert({signo, info});
342 
343  return SignalHandleUP(new SignalHandle(*this, signo));
344 #endif
345 }
346 
347 void MainLoop::UnregisterReadObject(IOObject::WaitableHandle handle) {
348  bool erased = m_read_fds.erase(handle);
350  assert(erased);
351 }
352 
353 void MainLoop::UnregisterSignal(int signo) {
354 #if SIGNAL_POLLING_UNSUPPORTED
355  Status("Signal polling is not supported on this platform.");
356 #else
357  auto it = m_signals.find(signo);
358  assert(it != m_signals.end());
359 
360  sigaction(signo, &it->second.old_action, nullptr);
361 
362  sigset_t set;
363  sigemptyset(&set);
364  sigaddset(&set, signo);
365  int ret = pthread_sigmask(it->second.was_blocked ? SIG_BLOCK : SIG_UNBLOCK,
366  &set, nullptr);
367  assert(ret == 0);
368  (void)ret;
369 
370 #if HAVE_SYS_EVENT_H
371  struct kevent ev;
372  EV_SET(&ev, signo, EVFILT_SIGNAL, EV_DELETE, 0, 0, 0);
373  ret = kevent(m_kqueue, &ev, 1, nullptr, 0, nullptr);
374  assert(ret == 0);
375 #endif
376 
377  m_signals.erase(it);
378 #endif
379 }
380 
381 Status MainLoop::Run() {
382  m_terminate_request = false;
383 
384  Status error;
385  RunImpl impl(*this);
386 
387  // run until termination or until we run out of things to listen to
388  while (!m_terminate_request && (!m_read_fds.empty() || !m_signals.empty())) {
389 
390  error = impl.Poll();
391  if (error.Fail())
392  return error;
393 
394  impl.ProcessEvents();
395  }
396  return Status();
397 }
398 
399 void MainLoop::ProcessSignal(int signo) {
400  auto it = m_signals.find(signo);
401  if (it != m_signals.end())
402  it->second.callback(*this); // Do the work
403 }
404 
405 void MainLoop::ProcessReadObject(IOObject::WaitableHandle handle) {
406  auto it = m_read_fds.find(handle);
407  if (it != m_read_fds.end())
408  it->second(*this); // Do the work
409 }
std::unique_ptr< SignalHandle > SignalHandleUP
Definition: MainLoop.h:39
#define UNUSED_IF_ASSERT_DISABLED(x)
Definition: lldb-defines.h:134
A class that represents a running process on the host machine.
llvm::DenseMap< IOObject::WaitableHandle, Callback > m_read_fds
Definition: MainLoop.h:100
#define POLL
Definition: MainLoop.cpp:40
void ProcessReadObject(IOObject::WaitableHandle handle)
Definition: MainLoop.cpp:405
static void SignalHandler(int signo, siginfo_t *info, void *)
Definition: MainLoop.cpp:66
POSIX error codes.
std::function< void(MainLoopBase &)> Callback
Definition: MainLoopBase.h:41
void ProcessSignal(int signo)
Definition: MainLoop.cpp:399
static llvm::raw_ostream & error(Stream &strm)
static sig_atomic_t g_signal_flags[NSIG]
Definition: MainLoop.cpp:63
void SetErrorString(llvm::StringRef err_str)
Set the current error string to err_str.
Definition: Status.cpp:242
std::unique_ptr< ReadHandle > ReadHandleUP
Definition: MainLoopBase.h:39
llvm::DenseMap< int, SignalInfo > m_signals
Definition: MainLoop.h:103
std::vector< struct pollfd > read_fds
Definition: MainLoop.cpp:92
bool Fail() const
Test for error condition.
Definition: Status.cpp:182
Definition: SBAddress.h:15
int SetErrorStringWithFormat(const char *format,...) __attribute__((format(printf
Set the current error string to a formatted error string.
Definition: Status.cpp:256
An error handling class.
Definition: Status.h:44