2 * Copyright 2017 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
18 * Subprocess library, modeled after Python's subprocess module
19 * (http://docs.python.org/2/library/subprocess.html)
21 * This library defines one class (Subprocess) which represents a child
22 * process. Subprocess has two constructors: one that takes a vector<string>
23 * and executes the given executable without using the shell, and one
24 * that takes a string and executes the given command using the shell.
25 * Subprocess allows you to redirect the child's standard input, standard
26 * output, and standard error to/from child descriptors in the parent,
27 * or to create communication pipes between the child and the parent.
29 * The simplest example is a thread-safe [1] version of the system() library
31 * Subprocess(cmd).wait();
32 * which executes the command using the default shell and waits for it
33 * to complete, returning the exit status.
35 * A thread-safe [1] version of popen() (type="r", to read from the child):
36 * Subprocess proc(cmd, Subprocess::pipeStdout());
37 * // read from proc.stdoutFd()
40 * A thread-safe [1] version of popen() (type="w", to write to the child):
41 * Subprocess proc(cmd, Subprocess::pipeStdin());
42 * // write to proc.stdinFd()
45 * If you want to redirect both stdin and stdout to pipes, you can, but note
46 * that you're subject to a variety of deadlocks. You'll want to use
47 * nonblocking I/O, like the callback version of communicate().
49 * The string or IOBuf-based variants of communicate() are the simplest way
50 * to communicate with a child via its standard input, standard output, and
51 * standard error. They buffer everything in memory, so they are not great
52 * for large amounts of data (or long-running processes), but they are much
53 * simpler than the callback version.
55 * == A note on thread-safety ==
57 * [1] "thread-safe" refers ONLY to the fact that Subprocess is very careful
58 * to fork in a way that does not cause grief in multithreaded programs.
60 * Caveat: If your system does not have the atomic pipe2 system call, it is
61 * not safe to concurrently call Subprocess from different threads.
62 * Therefore, it is best to have a single thread be responsible for spawning
65 * A particular instances of Subprocess is emphatically **not** thread-safe.
66 * If you need to simultaneously communicate via the pipes, and interact
67 * with the Subprocess state, your best bet is to:
68 * - takeOwnershipOfPipes() to separate the pipe I/O from the subprocess.
69 * - Only interact with the Subprocess from one thread at a time.
71 * The current implementation of communicate() cannot be safely interrupted.
72 * To do so correctly, one would need to use EventFD, or open a dedicated
73 * pipe to be messaged from a different thread -- in particular, kill() will
74 * not do, since a descendant may keep the pipes open indefinitely.
76 * So, once you call communicate(), you must wait for it to return, and not
77 * touch the pipes from other threads. closeParentFd() is emphatically
78 * unsafe to call concurrently, and even sendSignal() is not a good idea.
79 * You can perhaps give the Subprocess's PID to a different thread before
80 * starting communicate(), and use that PID to send a signal without
81 * accessing the Subprocess object. In that case, you will need a mutex
82 * that ensures you don't wait() before you sent said signal. In a
83 * nutshell, don't do this.
85 * In fact, signals are inherently concurrency-unsafe on Unix: if you signal
86 * a PID, while another thread is in waitpid(), the signal may fire either
87 * before or after the process is reaped. This means that your signal can,
88 * in pathological circumstances, be delivered to the wrong process (ouch!).
89 * To avoid this, you should only use non-blocking waits (i.e. poll()), and
90 * make sure to serialize your signals (i.e. kill()) with the waits --
91 * either wait & signal from the same thread, or use a mutex.
96 #include <sys/types.h>
108 #include <boost/container/flat_map.hpp>
109 #include <boost/operators.hpp>
111 #include <folly/Exception.h>
112 #include <folly/File.h>
113 #include <folly/FileUtil.h>
114 #include <folly/Function.h>
115 #include <folly/gen/String.h>
116 #include <folly/io/IOBufQueue.h>
117 #include <folly/MapUtil.h>
118 #include <folly/Portability.h>
119 #include <folly/Range.h>
124 * Class to wrap a process return code.
127 class ProcessReturnCode {
128 friend class Subprocess;
131 // Subprocess starts in the constructor, so this state designates only
132 // default-initialized or moved-out ProcessReturnCodes.
139 // Default-initialized for convenience. Subprocess::returnCode() will
140 // never produce this value.
141 ProcessReturnCode() : ProcessReturnCode(RV_NOT_STARTED) {}
143 // Trivially copyable
144 ProcessReturnCode(const ProcessReturnCode& p) = default;
145 ProcessReturnCode& operator=(const ProcessReturnCode& p) = default;
146 // Non-default move: In order for Subprocess to be movable, the "moved
147 // out" state must not be "running", or ~Subprocess() will abort.
148 ProcessReturnCode(ProcessReturnCode&& p) noexcept;
149 ProcessReturnCode& operator=(ProcessReturnCode&& p) noexcept;
152 * Process state. One of:
153 * NOT_STARTED: process hasn't been started successfully
154 * RUNNING: process is currently running
155 * EXITED: process exited (successfully or not)
156 * KILLED: process was killed by a signal.
161 * Helper wrappers around state().
163 bool notStarted() const { return state() == NOT_STARTED; }
164 bool running() const { return state() == RUNNING; }
165 bool exited() const { return state() == EXITED; }
166 bool killed() const { return state() == KILLED; }
169 * Exit status. Only valid if state() == EXITED; throws otherwise.
171 int exitStatus() const;
174 * Signal that caused the process's termination. Only valid if
175 * state() == KILLED; throws otherwise.
177 int killSignal() const;
180 * Was a core file generated? Only valid if state() == KILLED; throws
183 bool coreDumped() const;
186 * String representation; one of
189 * "exited with status <status>"
190 * "killed by signal <signal>"
191 * "killed by signal <signal> (core dumped)"
193 std::string str() const;
196 * Helper function to enforce a precondition based on this.
197 * Throws std::logic_error if in an unexpected state.
199 void enforce(State state) const;
201 explicit ProcessReturnCode(int rv) : rawStatus_(rv) { }
202 static constexpr int RV_NOT_STARTED = -2;
203 static constexpr int RV_RUNNING = -1;
209 * Base exception thrown by the Subprocess methods.
211 class SubprocessError : public std::exception {};
214 * Exception thrown by *Checked methods of Subprocess.
216 class CalledProcessError : public SubprocessError {
218 explicit CalledProcessError(ProcessReturnCode rc);
219 ~CalledProcessError() throw() = default;
220 const char* what() const throw() override { return what_.c_str(); }
221 ProcessReturnCode returnCode() const { return returnCode_; }
223 ProcessReturnCode returnCode_;
228 * Exception thrown if the subprocess cannot be started.
230 class SubprocessSpawnError : public SubprocessError {
232 SubprocessSpawnError(const char* executable, int errCode, int errnoValue);
233 ~SubprocessSpawnError() throw() = default;
234 const char* what() const throw() override { return what_.c_str(); }
235 int errnoValue() const { return errnoValue_; }
247 static const int CLOSE = -1;
248 static const int PIPE = -2;
249 static const int PIPE_IN = -3;
250 static const int PIPE_OUT = -4;
253 * See Subprocess::Options::dangerousPostForkPreExecCallback() for usage.
254 * Every derived class should include the following warning:
256 * DANGER: This class runs after fork in a child processes. Be fast, the
257 * parent thread is waiting, but remember that other parent threads are
258 * running and may mutate your state. Avoid mutating any data belonging to
259 * the parent. Avoid interacting with non-POD data that originated in the
260 * parent. Avoid any libraries that may internally reference non-POD data.
261 * Especially beware parent mutexes -- for example, glog's LOG() uses one.
263 struct DangerousPostForkPreExecCallback {
264 virtual ~DangerousPostForkPreExecCallback() {}
265 // This must return 0 on success, or an `errno` error code.
266 virtual int operator()() = 0;
270 * Class representing various options: file descriptor behavior, and
271 * whether to use $PATH for searching for the executable,
273 * By default, we don't use $PATH, file descriptors are closed if
274 * the close-on-exec flag is set (fcntl FD_CLOEXEC) and inherited
277 class Options : private boost::orable<Options> {
278 friend class Subprocess;
280 Options() {} // E.g. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58328
283 * Change action for file descriptor fd.
285 * "action" may be another file descriptor number (dup2()ed before the
286 * child execs), or one of CLOSE, PIPE_IN, and PIPE_OUT.
288 * CLOSE: close the file descriptor in the child
289 * PIPE_IN: open a pipe *from* the child
290 * PIPE_OUT: open a pipe *to* the child
292 * PIPE is a shortcut; same as PIPE_IN for stdin (fd 0), same as
293 * PIPE_OUT for stdout (fd 1) or stderr (fd 2), and an error for
294 * other file descriptors.
296 Options& fd(int fd, int action);
299 * Shortcut to change the action for standard input.
301 Options& stdinFd(int action) { return fd(STDIN_FILENO, action); }
304 * Shortcut to change the action for standard output.
306 Options& stdoutFd(int action) { return fd(STDOUT_FILENO, action); }
309 * Shortcut to change the action for standard error.
310 * Note that stderr(1) will redirect the standard error to the same
311 * file descriptor as standard output; the equivalent of bash's "2>&1"
313 Options& stderrFd(int action) { return fd(STDERR_FILENO, action); }
315 Options& pipeStdin() { return fd(STDIN_FILENO, PIPE_IN); }
316 Options& pipeStdout() { return fd(STDOUT_FILENO, PIPE_OUT); }
317 Options& pipeStderr() { return fd(STDERR_FILENO, PIPE_OUT); }
320 * Close all other fds (other than standard input, output, error,
321 * and file descriptors explicitly specified with fd()).
323 * This is potentially slow; it's generally a better idea to
324 * set the close-on-exec flag on all file descriptors that shouldn't
325 * be inherited by the child.
327 * Even with this option set, standard input, output, and error are
328 * not closed; use stdin(CLOSE), stdout(CLOSE), stderr(CLOSE) if you
331 Options& closeOtherFds() { closeOtherFds_ = true; return *this; }
334 * Use the search path ($PATH) when searching for the executable.
336 Options& usePath() { usePath_ = true; return *this; }
339 * Change the child's working directory, after the vfork.
341 Options& chdir(const std::string& dir) { childDir_ = dir; return *this; }
345 * Child will receive a signal when the parent exits.
347 Options& parentDeathSignal(int sig) {
348 parentDeathSignal_ = sig;
354 * Child will be made a process group leader when it starts. Upside: one
355 * can reliably all its kill non-daemonizing descendants. Downside: the
356 * child will not receive Ctrl-C etc during interactive use.
358 Options& processGroupLeader() {
359 processGroupLeader_ = true;
364 * *** READ THIS WHOLE DOCBLOCK BEFORE USING ***
366 * Run this callback in the child after the fork, just before the
367 * exec(), and after the child's state has been completely set up:
368 * - signal handlers have been reset to default handling and unblocked
369 * - the working directory was set
370 * - closed any file descriptors specified via Options()
371 * - set child process flags (see code)
373 * This is EXTREMELY DANGEROUS. For example, this innocuous-looking code
374 * can cause a fraction of your Subprocess launches to hang forever:
376 * LOG(INFO) << "Hello from the child";
378 * The reason is that glog has an internal mutex. If your fork() happens
379 * when the parent has the mutex locked, the child will wait forever.
383 * - Be quick -- the parent thread is blocked until you exit.
384 * - Remember that other parent threads are running, and may mutate your
386 * - Avoid mutating any data belonging to the parent.
387 * - Avoid interacting with non-POD data that came from the parent.
388 * - Avoid any libraries that may internally reference non-POD state.
389 * - Especially beware parent mutexes, e.g. LOG() uses a global mutex.
390 * - Avoid invoking the parent's destructors (you can accidentally
391 * delete files, terminate network connections, etc).
392 * - Read http://ewontfix.com/7/
394 Options& dangerousPostForkPreExecCallback(
395 DangerousPostForkPreExecCallback* cob) {
396 dangerousPostForkPreExecCallback_ = cob;
401 * Helpful way to combine Options.
403 Options& operator|=(const Options& other);
406 typedef boost::container::flat_map<int, int> FdMap;
408 bool closeOtherFds_{false};
409 bool usePath_{false};
410 std::string childDir_; // "" keeps the parent's working directory
412 int parentDeathSignal_{0};
414 bool processGroupLeader_{false};
415 DangerousPostForkPreExecCallback*
416 dangerousPostForkPreExecCallback_{nullptr};
419 static Options pipeStdin() { return Options().stdinFd(PIPE); }
420 static Options pipeStdout() { return Options().stdoutFd(PIPE); }
421 static Options pipeStderr() { return Options().stderrFd(PIPE); }
423 // Non-copiable, but movable
424 Subprocess(const Subprocess&) = delete;
425 Subprocess& operator=(const Subprocess&) = delete;
426 Subprocess(Subprocess&&) = default;
427 Subprocess& operator=(Subprocess&&) = default;
430 * Create an uninitialized subprocess.
432 * In this state it can only be destroyed, or assigned to using the move
433 * assignment operator.
438 * Create a subprocess from the given arguments. argv[0] must be listed.
439 * If not-null, executable must be the actual executable
440 * being used (otherwise it's the same as argv[0]).
442 * If env is not-null, it must contain name=value strings to be used
443 * as the child's environment; otherwise, we inherit the environment
444 * from the parent. env must be null if options.usePath is set.
447 const std::vector<std::string>& argv,
448 const Options& options = Options(),
449 const char* executable = nullptr,
450 const std::vector<std::string>* env = nullptr);
454 * Create a subprocess run as a shell command (as shell -c 'command')
456 * The shell to use is taken from the environment variable $SHELL,
457 * or /bin/sh if $SHELL is unset.
459 FOLLY_DEPRECATED("Prefer not running in a shell or use `shellify`.")
461 const std::string& cmd,
462 const Options& options = Options(),
463 const std::vector<std::string>* env = nullptr);
466 //// The methods below only manipulate the process state, and do not
467 //// affect its communication pipes.
471 * Return the child's pid, or -1 if the child wasn't successfully spawned
472 * or has already been wait()ed upon.
477 * Return the child's status (as per wait()) if the process has already
478 * been waited on, -1 if the process is still running, or -2 if the
479 * process hasn't been successfully started. NOTE that this does not call
480 * waitpid() or Subprocess::poll(), but simply returns the status stored
481 * in the Subprocess object.
483 ProcessReturnCode returnCode() const { return returnCode_; }
486 * Poll the child's status and return it. Return the exit status if the
487 * subprocess had quit, or RUNNING otherwise. Throws an std::logic_error
488 * if called on a Subprocess whose status is no longer RUNNING. No other
489 * exceptions are possible. Aborts on egregious violations of contract,
490 * e.g. if you wait for the underlying process without going through this
491 * Subprocess instance.
493 ProcessReturnCode poll();
496 * Poll the child's status. If the process is still running, return false.
497 * Otherwise, return true if the process exited with status 0 (success),
498 * or throw CalledProcessError if the process exited with a non-zero status.
503 * Wait for the process to terminate and return its status. Like poll(),
504 * the only exception this can throw is std::logic_error if you call this
505 * on a Subprocess whose status is RUNNING. Aborts on egregious
506 * violations of contract, like an out-of-band waitpid(p.pid(), 0, 0).
508 ProcessReturnCode wait();
511 * Wait for the process to terminate, throw if unsuccessful.
516 * Send a signal to the child. Shortcuts for the commonly used Unix
519 void sendSignal(int signal);
520 void terminate() { sendSignal(SIGTERM); }
521 void kill() { sendSignal(SIGKILL); }
524 //// The methods below only affect the process's communication pipes, but
525 //// not its return code or state (they do not poll() or wait()).
529 * Communicate with the child until all pipes to/from the child are closed.
531 * The input buffer is written to the process' stdin pipe, and data is read
532 * from the stdout and stderr pipes. Non-blocking I/O is performed on all
533 * pipes simultaneously to avoid deadlocks.
535 * The stdin pipe will be closed after the full input buffer has been written.
536 * An error will be thrown if a non-empty input buffer is supplied but stdin
537 * was not configured as a pipe.
539 * Returns a pair of buffers containing the data read from stdout and stderr.
540 * If stdout or stderr is not a pipe, an empty IOBuf queue will be returned
541 * for the respective buffer.
543 * Note that communicate() and communicateIOBuf() both return when all
544 * pipes to/from the child are closed; the child might stay alive after
545 * that, so you must still wait().
547 * communicateIOBuf() uses IOBufQueue for buffering (which has the
548 * advantage that it won't try to allocate all data at once), but it does
549 * store the subprocess's entire output in memory before returning.
551 * communicate() uses strings for simplicity.
553 std::pair<IOBufQueue, IOBufQueue> communicateIOBuf(
554 IOBufQueue input = IOBufQueue());
556 std::pair<std::string, std::string> communicate(
557 StringPiece input = StringPiece());
560 * Communicate with the child until all pipes to/from the child are closed.
564 * readCallback(pfd, cfd) will be called whenever there's data available
565 * on any pipe *from* the child (PIPE_OUT). pfd is the file descriptor
566 * in the parent (that you use to read from); cfd is the file descriptor
567 * in the child (used for identifying the stream; 1 = child's standard
568 * output, 2 = child's standard error, etc)
570 * writeCallback(pfd, cfd) will be called whenever a pipe *to* the child is
571 * writable (PIPE_IN). pfd is the file descriptor in the parent (that you
572 * use to write to); cfd is the file descriptor in the child (used for
573 * identifying the stream; 0 = child's standard input, etc)
575 * The read and write callbacks must read from / write to pfd and return
576 * false during normal operation. Return true to tell communicate() to
577 * close the pipe. For readCallback, this might send SIGPIPE to the
578 * child, or make its writes fail with EPIPE, so you should generally
579 * avoid returning true unless you've reached end-of-file.
581 * communicate() returns when all pipes to/from the child are closed; the
582 * child might stay alive after that, so you must still wait().
583 * Conversely, the child may quit long before its pipes are closed, since
584 * its descendants can keep them alive forever.
586 * Most users won't need to use this callback version; the simpler version
587 * of communicate (which buffers data in memory) will probably work fine.
589 * == Things you must get correct ==
591 * 1) You MUST consume all data passed to readCallback (or return true to
592 * close the pipe). Similarly, you MUST write to a writable pipe (or
593 * return true to close the pipe). To do otherwise is an error that can
594 * result in a deadlock. You must do this even for pipes you are not
597 * 2) pfd is nonblocking, so be prepared for read() / write() to return -1
598 * and set errno to EAGAIN (in which case you should return false). Use
599 * readNoInt() from FileUtil.h to handle interrupted reads for you.
601 * 3) Your callbacks MUST NOT call any of the Subprocess methods that
602 * manipulate the pipe FDs. Check the docblocks, but, for example,
603 * neither closeParentFd (return true instead) nor takeOwnershipOfPipes
604 * are safe. Stick to reading/writing from pfd, as appropriate.
608 * 1) See ReadLinesCallback for an easy way to consume the child's output
609 * streams line-by-line (or tokenized by another delimiter).
611 * 2) "Wait until the descendants close the pipes" is usually the behavior
612 * you want, since the descendants may have something to say even if the
613 * immediate child is dead. If you need to be able to force-close all
614 * parent FDs, communicate() will NOT work for you. Do it your own way by
615 * using takeOwnershipOfPipes().
617 * Why not? You can return "true" from your callbacks to sever active
618 * pipes, but inactive ones can remain open indefinitely. It is
619 * impossible to safely close inactive pipes while another thread is
620 * blocked in communicate(). This is BY DESIGN. Racing communicate()'s
621 * read/write callbacks can result in wrong I/O and data corruption. This
622 * class would need internal synchronization and timeouts, a poor and
623 * expensive implementation choice, in order to make closeParentFd()
626 using FdCallback = folly::Function<bool(int, int)>;
627 void communicate(FdCallback readCallback, FdCallback writeCallback);
630 * A readCallback for Subprocess::communicate() that helps you consume
631 * lines (or other delimited pieces) from your subprocess's file
632 * descriptors. Use the readLinesCallback() helper to get template
633 * deduction. For example:
635 * subprocess.communicate(
636 * Subprocess::readLinesCallback(
637 * [](int fd, folly::StringPiece s) {
638 * std::cout << fd << " said: " << s;
639 * return false; // Keep reading from the child
642 * [](int pdf, int cfd){ return true; } // Don't write to the child
645 * If a file line exceeds maxLineLength, your callback will get some
646 * initial chunks of maxLineLength with no trailing delimiters. The final
647 * chunk of a line is delimiter-terminated iff the delimiter was present
648 * in the input. In particular, the last line in a file always lacks a
649 * delimiter -- so if a file ends on a delimiter, the final line is empty.
651 * Like a regular communicate() callback, your fdLineCb() normally returns
652 * false. It may return true to tell Subprocess to close the underlying
653 * file descriptor. The child process may then receive SIGPIPE or get
654 * EPIPE errors on writes.
656 template <class Callback>
657 class ReadLinesCallback {
659 // Binds an FD to the client-provided FD+line callback
660 struct StreamSplitterCallback {
661 StreamSplitterCallback(Callback& cb, int fd) : cb_(cb), fd_(fd) { }
662 // The return value semantics are inverted vs StreamSplitter
663 bool operator()(StringPiece s) { return !cb_(fd_, s); }
667 typedef gen::StreamSplitter<StreamSplitterCallback> LineSplitter;
669 explicit ReadLinesCallback(
671 uint64_t maxLineLength = 0, // No line length limit by default
672 char delimiter = '\n',
673 uint64_t bufSize = 1024
674 ) : fdLineCb_(std::forward<Callback>(fdLineCb)),
675 maxLineLength_(maxLineLength),
676 delimiter_(delimiter),
679 bool operator()(int pfd, int cfd) {
680 // Make a splitter for this cfd if it doesn't already exist
681 auto it = fdToSplitter_.find(cfd);
682 auto& splitter = (it != fdToSplitter_.end()) ? it->second
683 : fdToSplitter_.emplace(cfd, LineSplitter(
684 delimiter_, StreamSplitterCallback(fdLineCb_, cfd), maxLineLength_
686 // Read as much as we can from this FD
689 ssize_t ret = readNoInt(pfd, buf, bufSize_);
690 if (ret == -1 && errno == EAGAIN) { // No more data for now
693 checkUnixError(ret, "read");
694 if (ret == 0) { // Reached end-of-file
695 splitter.flush(); // Ignore return since the file is over anyway
698 if (!splitter(StringPiece(buf, ret))) {
699 return true; // The callback told us to stop
706 const uint64_t maxLineLength_;
707 const char delimiter_;
708 const uint64_t bufSize_;
709 // We lazily make splitters for all cfds that get used.
710 std::unordered_map<int, LineSplitter> fdToSplitter_;
713 // Helper to enable template deduction
714 template <class Callback>
715 static auto readLinesCallback(
717 uint64_t maxLineLength = 0, // No line length limit by default
718 char delimiter = '\n',
719 uint64_t bufSize = 1024)
720 -> ReadLinesCallback<typename std::decay<Callback>::type> {
721 return ReadLinesCallback<typename std::decay<Callback>::type>(
722 std::forward<Callback>(fdLineCb), maxLineLength, delimiter, bufSize);
726 * communicate() callbacks can use this to temporarily enable/disable
727 * notifications (callbacks) for a pipe to/from the child. By default,
728 * all are enabled. Useful for "chatty" communication -- you want to
729 * disable write callbacks until you receive the expected message.
731 * Disabling a pipe does not free you from the requirement to consume all
732 * incoming data. Failing to do so will easily create deadlock bugs.
734 * Throws if the childFd is not known.
736 void enableNotifications(int childFd, bool enabled);
739 * Are notifications for one pipe to/from child enabled? Throws if the
740 * childFd is not known.
742 bool notificationsEnabled(int childFd) const;
745 //// The following methods are meant for the cases when communicate() is
746 //// not suitable. You should not need them when you call communicate(),
747 //// and, in fact, it is INHERENTLY UNSAFE to use closeParentFd() or
748 //// takeOwnershipOfPipes() from a communicate() callback.
752 * Close the parent file descriptor given a file descriptor in the child.
753 * DO NOT USE from communicate() callbacks; make them return true instead.
755 void closeParentFd(int childFd);
758 * Set all pipes from / to child to be non-blocking. communicate() does
761 void setAllNonBlocking();
764 * Get parent file descriptor corresponding to the given file descriptor
765 * in the child. Throws if childFd isn't a pipe (PIPE_IN / PIPE_OUT).
766 * Do not close() the returned file descriptor; use closeParentFd, above.
768 int parentFd(int childFd) const {
769 return pipes_[findByChildFd(childFd)].pipe.fd();
771 int stdinFd() const { return parentFd(0); }
772 int stdoutFd() const { return parentFd(1); }
773 int stderrFd() const { return parentFd(2); }
776 * The child's pipes are logically separate from the process metadata
777 * (they may even be kept alive by the child's descendants). This call
778 * lets you manage the pipes' lifetime separetely from the lifetime of the
781 * After this call, the Subprocess instance will have no knowledge of
782 * these pipes, and the caller assumes responsibility for managing their
783 * lifetimes. Pro-tip: prefer to explicitly close() the pipes, since
784 * folly::File would otherwise silently suppress I/O errors.
786 * No, you may NOT call this from a communicate() callback.
789 ChildPipe(int fd, folly::File&& ppe) : childFd(fd), pipe(std::move(ppe)) {}
791 folly::File pipe; // Owns the parent FD
793 std::vector<ChildPipe> takeOwnershipOfPipes();
796 static const int RV_RUNNING = ProcessReturnCode::RV_RUNNING;
797 static const int RV_NOT_STARTED = ProcessReturnCode::RV_NOT_STARTED;
799 // spawn() sets up a pipe to read errors from the child,
800 // then calls spawnInternal() to do the bulk of the work. Once
801 // spawnInternal() returns it reads the error pipe to see if the child
802 // encountered any errors.
804 std::unique_ptr<const char*[]> argv,
805 const char* executable,
806 const Options& options,
807 const std::vector<std::string>* env);
809 std::unique_ptr<const char*[]> argv,
810 const char* executable,
812 const std::vector<std::string>* env,
815 // Actions to run in child.
816 // Note that this runs after vfork(), so tread lightly.
817 // Returns 0 on success, or an errno value on failure.
818 int prepareChild(const Options& options,
819 const sigset_t* sigmask,
820 const char* childDir) const;
821 int runChild(const char* executable, char** argv, char** env,
822 const Options& options) const;
825 * Read from the error pipe, and throw SubprocessSpawnError if the child
826 * failed before calling exec().
828 void readChildErrorPipe(int pfd, const char* executable);
830 // Returns an index into pipes_. Throws std::invalid_argument if not found.
831 size_t findByChildFd(const int childFd) const;
834 ProcessReturnCode returnCode_{RV_NOT_STARTED};
837 * Represents a pipe between this process, and the child process (or its
838 * descendant). To interact with these pipes, you can use communicate(),
839 * or use parentFd() and related methods, or separate them from the
840 * Subprocess instance entirely via takeOwnershipOfPipes().
842 struct Pipe : private boost::totally_ordered<Pipe> {
843 folly::File pipe; // Our end of the pipe, wrapped in a File to auto-close.
844 int childFd = -1; // Identifies the pipe: what FD is this in the child?
845 int direction = PIPE_IN; // one of PIPE_IN / PIPE_OUT
846 bool enabled = true; // Are notifications enabled in communicate()?
848 bool operator<(const Pipe& other) const {
849 return childFd < other.childFd;
851 bool operator==(const Pipe& other) const {
852 return childFd == other.childFd;
856 // Populated at process start according to fdActions, empty after
857 // takeOwnershipOfPipes(). Sorted by childFd. Can only have elements
858 // erased, but not inserted, after being populated.
860 // The number of pipes between parent and child is assumed to be small,
861 // so we're happy with a vector here, even if it means linear erase.
862 std::vector<Pipe> pipes_;
865 inline Subprocess::Options& Subprocess::Options::operator|=(
866 const Subprocess::Options& other) {
867 if (this == &other) return *this;
869 for (auto& p : other.fdActions_) {
870 fdActions_[p.first] = p.second;
872 closeOtherFds_ |= other.closeOtherFds_;
873 usePath_ |= other.usePath_;
874 processGroupLeader_ |= other.processGroupLeader_;