remoting/host/posix/signal_handler.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // TODO(jamiewalch): Add unit tests for this.
   6
   7 #include "remoting/host/posix/signal_handler.h"
   8
   9 #include <errno.h>
  10 #include <signal.h>
  11
  12 #include <list>
  13 #include <utility>
  14
  15 #include "base/compiler_specific.h"
  16 #include "base/message_loop/message_loop.h"
  17 #include "base/message_loop/message_pump_libevent.h"
  18 #include "base/posix/eintr_wrapper.h"
  19 #include "base/threading/platform_thread.h"
  20
  21 namespace remoting {
  22 namespace {
  23
  24 class SignalListener : public base::MessagePumpLibevent::Watcher {
  25  public:
  26   SignalListener();
  27
  28   void AddSignalHandler(int signal, const SignalHandler& handler);
  29
  30   void OnFileCanReadWithoutBlocking(int fd) override;
  31   void OnFileCanWriteWithoutBlocking(int fd) override {}
  32
  33   // WatchFileDescriptor needs a controller through which the operation can be
  34   // canceled. We don't use it, but this is as good a place as any to store it.
  35   base::MessagePumpLibevent::FileDescriptorWatcher controller;
  36
  37  private:
  38   typedef std::pair<int, SignalHandler> SignalAndHandler;
  39   typedef std::list<SignalAndHandler> SignalHandlers;
  40   SignalHandlers signal_handlers_;
  41 };
  42
  43 SignalListener::SignalListener() {
  44 }
  45
  46 void SignalListener::AddSignalHandler(int signal,
  47                                       const SignalHandler& handler) {
  48   signal_handlers_.push_back(SignalAndHandler(signal, handler));
  49 }
  50
  51 void SignalListener::OnFileCanReadWithoutBlocking(int fd) {
  52   char buffer;
  53   int result = HANDLE_EINTR(read(fd, &buffer, sizeof(buffer)));
  54   if (result > 0) {
  55     for (SignalHandlers::const_iterator i = signal_handlers_.begin();
  56          i != signal_handlers_.end();
  57          ++i) {
  58       if (i->first == buffer) {
  59         i->second.Run(i->first);
  60       }
  61     }
  62   }
  63 }
  64
  65 SignalListener* g_signal_listener = nullptr;
  66 int g_write_fd = 0;
  67
  68 void GlobalSignalHandler(int signal) {
  69   char byte = signal;
  70   ignore_result(write(g_write_fd, &byte, 1));
  71 }
  72
  73 }  // namespace
  74
  75 // RegisterSignalHandler registers a signal handler that writes a byte to a
  76 // pipe each time a signal is received. The read end of the pipe is registered
  77 // with the current MessageLoop (which must be of type IO); whenever the pipe
  78 // is readable, it invokes the specified callback.
  79 //
  80 // This arrangement is required because the set of system APIs that are safe to
  81 // call from a signal handler is very limited (but does include write).
  82 bool RegisterSignalHandler(int signal_number, const SignalHandler& handler) {
  83   CHECK(signal_number < 256);  // Don't want to worry about multi-byte writes.
  84   if (!g_signal_listener) {
  85     g_signal_listener = new SignalListener();
  86   }
  87   if (!g_write_fd) {
  88     int pipe_fd[2];
  89     int result = pipe(pipe_fd);
  90     if (result < 0) {
  91       LOG(ERROR) << "Could not create signal pipe: " << errno;
  92       return false;
  93     }
  94     base::MessageLoopForIO* message_loop = base::MessageLoopForIO::current();
  95     result =
  96         message_loop->WatchFileDescriptor(pipe_fd[0],
  97                                           true,
  98                                           base::MessageLoopForIO::WATCH_READ,
  99                                           &g_signal_listener->controller,
 100                                           g_signal_listener);
 101     if (!result) {
 102       LOG(ERROR) << "Failed to create signal detector task.";
 103       close(pipe_fd[0]);
 104       close(pipe_fd[1]);
 105       return false;
 106     }
 107     g_write_fd = pipe_fd[1];
 108   }
 109   if (signal(signal_number, GlobalSignalHandler) == SIG_ERR) {
 110     LOG(ERROR) << "signal() failed: " << errno;
 111     return false;
 112   }
 113   g_signal_listener->AddSignalHandler(signal_number, handler);
 114   return true;
 115 }
 116
 117 }  // namespace remoting