process-cpp 3.0.0
A simple convenience library for handling processes in C++11.
child_process.cpp
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1/*
2 * Copyright © 2013 Canonical Ltd.
3 *
4 * This program is free software: you can redistribute it and/or modify it
5 * under the terms of the GNU Lesser General Public License version 3,
6 * as published by the Free Software Foundation.
7 *
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 * GNU Lesser General Public License for more details.
12 *
13 * You should have received a copy of the GNU Lesser General Public License
14 * along with this program. If not, see <http://www.gnu.org/licenses/>.
15 *
16 * Authored by: Thomas Voß <thomas.voss@canonical.com>
17 */
18
20
21#include <boost/iostreams/device/file_descriptor.hpp>
22#include <boost/iostreams/stream.hpp>
23
24#include <atomic>
25#include <fstream>
26#include <mutex>
27#include <unordered_map>
28
29#include <fcntl.h>
30#include <poll.h>
31#include <unistd.h>
32
33#include <sys/eventfd.h>
34#include <sys/signalfd.h>
35
36namespace io = boost::iostreams;
37
38namespace
39{
40
41struct DeathObserverImpl : public core::posix::ChildProcess::DeathObserver
42{
43 DeathObserverImpl(const std::shared_ptr<core::posix::SignalTrap>& trap)
44 : on_sig_child_connection
45 {
46 trap->signal_raised().connect([this](core::posix::Signal signal)
47 {
48 switch (signal)
49 {
52 break;
53 default:
54 break;
55 }
56 })
57 }
58 {
59 if (!trap->has(core::posix::Signal::sig_chld))
60 throw std::logic_error(
61 "DeathObserver::DeathObserverImpl: Given SignalTrap"
62 " instance does not trap Signal::sig_chld.");
63 }
64
65 bool add(const core::posix::ChildProcess& process) override
66 {
67 if (process.pid() == -1)
68 return false;
69
70 std::lock_guard<std::mutex> lg(guard);
71
72 bool added = false;
73 auto new_process = std::make_pair(process.pid(), process);
74 std::tie(std::ignore, added) = children.insert(new_process);
75
76 if (added)
77 {
78 // The process may have died between it's instantiation and it
79 // being added to the children map. Check that it's still alive.
80 int status{-1};
81 if (::waitpid(process.pid(), &status, WNOHANG) != 0) // child no longer alive
82 {
83 // we missed the SIGCHLD signal so we must now manually
84 // inform our subscribers.
85 signals.child_died(new_process.second);
86 children.erase(new_process.first);
87 return false;
88 }
89 }
90
91 return added;
92 }
93
94 bool has(const core::posix::ChildProcess& process) const override
95 {
96 std::lock_guard<std::mutex> lg(guard);
97 return children.count(process.pid()) > 0;
98 }
99
100 const core::Signal<core::posix::ChildProcess>& child_died() const override
101 {
102 return signals.child_died;
103 }
104
105 void on_sig_child() override
106 {
107 pid_t pid{-1}; int status{-1};
108 while (true)
109 {
110 pid = ::waitpid(0, &status, WNOHANG);
111
112 if (pid == -1)
113 {
114 if (errno == ECHILD)
115 {
116 break; // No more children
117 }
118 continue; // Ignore stray SIGCHLD signals
119 }
120 else if (pid == 0)
121 {
122 break; // No more children
123 }
124 else
125 {
126 std::lock_guard<std::mutex> lg(guard);
127 auto it = children.find(pid);
128
129 if (it != children.end())
130 {
131 if (WIFSIGNALED(status) || WIFEXITED(status))
132 {
133 signals.child_died(it->second);
134 children.erase(it);
135 }
136 }
137 }
138 }
139 }
140
141 mutable std::mutex guard;
142 std::unordered_map<pid_t, core::posix::ChildProcess> children;
143 core::ScopedConnection on_sig_child_connection;
144 struct
145 {
146 core::Signal<core::posix::ChildProcess> child_died;
147 } signals;
148};
149}
150
151std::unique_ptr<core::posix::ChildProcess::DeathObserver>
153 std::shared_ptr<core::posix::SignalTrap> trap)
154{
155 static std::atomic<bool> has_been_created_once{false};
156
157 if (has_been_created_once.exchange(true))
158 throw std::runtime_error
159 {
160 "DeathObserver::create_once_with_signal_trap: "
161 "Cannot create more than one instance."
162 };
163
164 try
165 {
166 std::unique_ptr<core::posix::ChildProcess::DeathObserver> result
167 {
168 new DeathObserverImpl{trap}
169 };
170
171 return result;
172 } catch(...)
173 {
174 // We make sure that a throwing c'tor does not impact our ability to
175 // retry creation of a DeathObserver instance.
176 has_been_created_once.store(false);
177
178 std::rethrow_exception(std::current_exception());
179 }
180
181 assert(false && "We should never reach here.");
182
183 // Silence the compiler.
184 return std::unique_ptr<core::posix::ChildProcess::DeathObserver>{};
185}
186
187namespace core
188{
189namespace posix
190{
191ChildProcess::Pipe ChildProcess::Pipe::invalid()
192{
193 static Pipe p;
194 static std::once_flag flag;
195
196 std::call_once(flag, [&]() { p.close_read_fd(); p.close_write_fd(); });
197
198 return p;
199}
200
201ChildProcess::Pipe::Pipe()
202{
203 int rc = ::pipe(fds);
204
205 if (rc == -1)
206 throw std::system_error(errno, std::system_category());
207}
208
209ChildProcess::Pipe::Pipe(const ChildProcess::Pipe& rhs) : fds{-1, -1}
210{
211 if (rhs.fds[0] != -1)
212 fds[0] = ::dup(rhs.fds[0]);
213
214 if (rhs.fds[1] != -1)
215 fds[1] = ::dup(rhs.fds[1]);
216}
217
218ChildProcess::Pipe::~Pipe()
219{
220 if (fds[0] != -1)
221 ::close(fds[0]);
222 if (fds[1] != -1)
223 ::close(fds[1]);
224}
225
226int ChildProcess::Pipe::read_fd() const
227{
228 return fds[0];
229}
230
231void ChildProcess::Pipe::close_read_fd()
232{
233 if (fds[0] != -1)
234 {
235 ::close(fds[0]);
236 fds[0] = -1;
237 }
238}
239
240int ChildProcess::Pipe::write_fd() const
241{
242 return fds[1];
243}
244
245void ChildProcess::Pipe::close_write_fd()
246{
247 if (fds[1] != -1)
248 {
249 ::close(fds[1]);
250 fds[1] = -1;
251 }
252}
253
254ChildProcess::Pipe& ChildProcess::Pipe::operator=(const ChildProcess::Pipe& rhs)
255{
256 if (fds[0] != -1)
257 ::close(fds[0]);
258 if (fds[1] != -1)
259 ::close(fds[1]);
260
261 if (rhs.fds[0] != -1)
262 fds[0] = ::dup(rhs.fds[0]);
263 else
264 fds[0] = -1;
265 if (rhs.fds[1] != -1)
266 fds[1] = ::dup(rhs.fds[1]);
267 else
268 fds[1] = -1;
269
270 return *this;
271}
272
274{
275 // stdin and stdout are always "relative" to the childprocess, i.e., we
276 // write to stdin of the child process and read from its stdout.
277 Private(pid_t pid,
278 const ChildProcess::Pipe& stderr,
279 const ChildProcess::Pipe& stdin,
280 const ChildProcess::Pipe& stdout)
281 : pipes{stderr, stdin, stdout},
282 serr(pipes.stderr.read_fd(), io::never_close_handle),
283 sin(pipes.stdin.write_fd(), io::never_close_handle),
284 sout(pipes.stdout.read_fd(), io::never_close_handle),
285 cerr(&serr),
286 cin(&sin),
287 cout(&sout),
288 original_parent_pid(::getpid()),
289 original_child_pid(pid)
290 {
291 }
292
294 {
295 // Check if we are in the original parent process.
296 if (original_parent_pid == getpid())
297 {
298 // If so, check if we are considering a valid pid here.
299 // If so, we kill the original child.
300 if (original_child_pid != -1)
301 ::kill(original_child_pid, SIGKILL);
302 }
303 }
304
305 struct
306 {
307 ChildProcess::Pipe stdin;
308 ChildProcess::Pipe stdout;
309 ChildProcess::Pipe stderr;
310 } pipes;
311 io::stream_buffer<io::file_descriptor_source> serr;
312 io::stream_buffer<io::file_descriptor_sink> sin;
313 io::stream_buffer<io::file_descriptor_source> sout;
314 std::istream cerr;
315 std::ostream cin;
316 std::istream cout;
317
318 // We need to store the original parent pid as we might have been forked
319 // and with our automatic cleanup in place, it might happen that the d'tor
320 // is called from the child process.
323};
324
326{
327 // We take the init process as child.
328 static const pid_t invalid_pid = 1;
329 return ChildProcess(invalid_pid, Pipe::invalid(), Pipe::invalid(), Pipe::invalid());
330}
331
332ChildProcess::ChildProcess(pid_t pid,
333 const ChildProcess::Pipe& stdin_pipe,
334 const ChildProcess::Pipe& stdout_pipe,
335 const ChildProcess::Pipe& stderr_pipe)
336 : Process(pid),
337 d(new Private{pid, stdin_pipe, stdout_pipe, stderr_pipe})
338{
339}
340
342{
343}
344
346{
347 int status = -1;
348 pid_t result_pid = ::waitpid(pid(), std::addressof(status), static_cast<int>(flags));
349
350 if (result_pid == -1)
351 throw std::system_error(errno, std::system_category());
352
353 wait::Result result;
354
355 if (result_pid == 0)
356 {
358 return result;
359 }
360
361 if (WIFEXITED(status))
362 {
364 result.detail.if_exited.status = static_cast<exit::Status>(WEXITSTATUS(status));
365 } else if (WIFSIGNALED(status))
366 {
368 result.detail.if_signaled.signal = static_cast<Signal>(WTERMSIG(status));
369 result.detail.if_signaled.core_dumped = WCOREDUMP(status);
370 } else if (WIFSTOPPED(status))
371 {
373 result.detail.if_stopped.signal = static_cast<Signal>(WSTOPSIG(status));
374 } else if (WIFCONTINUED(status))
375 {
377 }
378
379 return result;
380}
381
382std::istream& ChildProcess::cerr()
383{
384 return d->cerr;
385}
386
387std::ostream& ChildProcess::cin()
388{
389 return d->cin;
390}
391
392std::istream& ChildProcess::cout()
393{
394 return d->cout;
395}
396}
397}
The DeathObserver class observes child process' states and emits a signal when a monitored child has ...
Definition: child_process.h:57
virtual bool add(const ChildProcess &child)=0
add adds the specified child to the list of observed child processes.
static std::unique_ptr< DeathObserver > create_once_with_signal_trap(std::shared_ptr< SignalTrap > trap)
Creates the unique instance of class DeathObserver.
virtual bool has(const ChildProcess &child) const =0
has checks whether the specified child is observed.
virtual void on_sig_child()=0
Checks and reaps all child processes registered with the observer instance.
virtual const core::Signal< ChildProcess > & child_died() const =0
child_died is emitted whenever an observed child ceases to exist.
The Process class models a child process of this process.
Definition: child_process.h:44
static ChildProcess invalid()
Creates an invalid ChildProcess.
wait::Result wait_for(const wait::Flags &flags)
Wait for the child process to change state.
std::ostream & cin()
Access this process's stdin.
std::istream & cerr()
Access this process's stderr.
std::istream & cout()
Access this process's stdout.
The Process class models a process and possible operations on it.
Definition: process.h:45
virtual pid_t pid() const
Query the pid of the process.
Definition: process.cpp:59
Status
The Status enum wrap's the posix exit status.
Definition: exit.h:34
Flags
Flags enumerates different behavior when waiting for a child process to change state.
Definition: wait.h:43
Signal
The Signal enum collects the most common POSIX signals.
Definition: signal.h:39
io::stream_buffer< io::file_descriptor_source > sout
io::stream_buffer< io::file_descriptor_sink > sin
io::stream_buffer< io::file_descriptor_source > serr
Private(pid_t pid, const ChildProcess::Pipe &stderr, const ChildProcess::Pipe &stdin, const ChildProcess::Pipe &stdout)
The Result struct encapsulates the result of waiting for a process state change.
Definition: wait.h:55
bool core_dumped
true if the process termination resulted in a core dump.
Definition: wait.h:88
@ signaled
The process was signalled and terminated.
@ no_state_change
No state change occurred.
@ exited
The process exited normally.
@ continued
The process resumed operation.
@ stopped
The process was signalled and stopped.
union core::posix::wait::Result::@4 detail
Union of result-specific details.
struct core::posix::wait::Result::@4::@6 if_signaled
enum core::posix::wait::Result::Status status
Signal signal
Signal that caused the process to terminate.
Definition: wait.h:87
struct core::posix::wait::Result::@4::@5 if_exited
struct core::posix::wait::Result::@4::@7 if_stopped