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::Options().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::Options().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.
97 #include <sys/types.h>
100 #include <sys/wait.h>
109 #include <boost/container/flat_map.hpp>
111 #include <folly/Exception.h>
112 #include <folly/File.h>
113 #include <folly/FileUtil.h>
114 #include <folly/Function.h>
115 #include <folly/MapUtil.h>
116 #include <folly/Optional.h>
117 #include <folly/Portability.h>
118 #include <folly/Range.h>
119 #include <folly/gen/String.h>
120 #include <folly/io/IOBufQueue.h>
121 #include <folly/portability/SysResource.h>
126 * Class to wrap a process return code.
129 class ProcessReturnCode {
132 // Subprocess starts in the constructor, so this state designates only
133 // default-initialized or moved-out ProcessReturnCodes.
140 static ProcessReturnCode makeNotStarted() {
141 return ProcessReturnCode(RV_NOT_STARTED);
144 static ProcessReturnCode makeRunning() {
145 return ProcessReturnCode(RV_RUNNING);
148 static ProcessReturnCode make(int status);
150 // Default-initialized for convenience. Subprocess::returnCode() will
151 // never produce this value.
152 ProcessReturnCode() : rawStatus_(RV_NOT_STARTED) {}
154 // Trivially copyable
155 ProcessReturnCode(const ProcessReturnCode& p) = default;
156 ProcessReturnCode& operator=(const ProcessReturnCode& p) = default;
157 // Non-default move: In order for Subprocess to be movable, the "moved
158 // out" state must not be "running", or ~Subprocess() will abort.
159 ProcessReturnCode(ProcessReturnCode&& p) noexcept;
160 ProcessReturnCode& operator=(ProcessReturnCode&& p) noexcept;
163 * Process state. One of:
164 * NOT_STARTED: process hasn't been started successfully
165 * RUNNING: process is currently running
166 * EXITED: process exited (successfully or not)
167 * KILLED: process was killed by a signal.
172 * Helper wrappers around state().
174 bool notStarted() const { return state() == NOT_STARTED; }
175 bool running() const { return state() == RUNNING; }
176 bool exited() const { return state() == EXITED; }
177 bool killed() const { return state() == KILLED; }
180 * Exit status. Only valid if state() == EXITED; throws otherwise.
182 int exitStatus() const;
185 * Signal that caused the process's termination. Only valid if
186 * state() == KILLED; throws otherwise.
188 int killSignal() const;
191 * Was a core file generated? Only valid if state() == KILLED; throws
194 bool coreDumped() const;
197 * String representation; one of
200 * "exited with status <status>"
201 * "killed by signal <signal>"
202 * "killed by signal <signal> (core dumped)"
204 std::string str() const;
207 * Helper function to enforce a precondition based on this.
208 * Throws std::logic_error if in an unexpected state.
210 void enforce(State state) const;
212 explicit ProcessReturnCode(int rv) : rawStatus_(rv) { }
213 static constexpr int RV_NOT_STARTED = -2;
214 static constexpr int RV_RUNNING = -1;
220 * Base exception thrown by the Subprocess methods.
222 class SubprocessError : public std::runtime_error {
224 using std::runtime_error::runtime_error;
228 * Exception thrown by *Checked methods of Subprocess.
230 class CalledProcessError : public SubprocessError {
232 explicit CalledProcessError(ProcessReturnCode rc);
233 ~CalledProcessError() throw() override = default;
234 ProcessReturnCode returnCode() const { return returnCode_; }
236 ProcessReturnCode returnCode_;
240 * Exception thrown if the subprocess cannot be started.
242 class SubprocessSpawnError : public SubprocessError {
244 SubprocessSpawnError(const char* executable, int errCode, int errnoValue);
245 ~SubprocessSpawnError() throw() override = default;
246 int errnoValue() const { return errnoValue_; }
257 static const int CLOSE = -1;
258 static const int PIPE = -2;
259 static const int PIPE_IN = -3;
260 static const int PIPE_OUT = -4;
263 * See Subprocess::Options::dangerousPostForkPreExecCallback() for usage.
264 * Every derived class should include the following warning:
266 * DANGER: This class runs after fork in a child processes. Be fast, the
267 * parent thread is waiting, but remember that other parent threads are
268 * running and may mutate your state. Avoid mutating any data belonging to
269 * the parent. Avoid interacting with non-POD data that originated in the
270 * parent. Avoid any libraries that may internally reference non-POD data.
271 * Especially beware parent mutexes -- for example, glog's LOG() uses one.
273 struct DangerousPostForkPreExecCallback {
274 virtual ~DangerousPostForkPreExecCallback() {}
275 // This must return 0 on success, or an `errno` error code.
276 virtual int operator()() = 0;
280 * Class representing various options: file descriptor behavior, and
281 * whether to use $PATH for searching for the executable,
283 * By default, we don't use $PATH, file descriptors are closed if
284 * the close-on-exec flag is set (fcntl FD_CLOEXEC) and inherited
288 friend class Subprocess;
290 Options() {} // E.g. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58328
293 * Change action for file descriptor fd.
295 * "action" may be another file descriptor number (dup2()ed before the
296 * child execs), or one of CLOSE, PIPE_IN, and PIPE_OUT.
298 * CLOSE: close the file descriptor in the child
299 * PIPE_IN: open a pipe *from* the child
300 * PIPE_OUT: open a pipe *to* the child
302 * PIPE is a shortcut; same as PIPE_IN for stdin (fd 0), same as
303 * PIPE_OUT for stdout (fd 1) or stderr (fd 2), and an error for
304 * other file descriptors.
306 Options& fd(int fd, int action);
309 * Shortcut to change the action for standard input.
311 Options& stdinFd(int action) { return fd(STDIN_FILENO, action); }
314 * Shortcut to change the action for standard output.
316 Options& stdoutFd(int action) { return fd(STDOUT_FILENO, action); }
319 * Shortcut to change the action for standard error.
320 * Note that stderr(1) will redirect the standard error to the same
321 * file descriptor as standard output; the equivalent of bash's "2>&1"
323 Options& stderrFd(int action) { return fd(STDERR_FILENO, action); }
325 Options& pipeStdin() { return fd(STDIN_FILENO, PIPE_IN); }
326 Options& pipeStdout() { return fd(STDOUT_FILENO, PIPE_OUT); }
327 Options& pipeStderr() { return fd(STDERR_FILENO, PIPE_OUT); }
330 * Close all other fds (other than standard input, output, error,
331 * and file descriptors explicitly specified with fd()).
333 * This is potentially slow; it's generally a better idea to
334 * set the close-on-exec flag on all file descriptors that shouldn't
335 * be inherited by the child.
337 * Even with this option set, standard input, output, and error are
338 * not closed; use stdin(CLOSE), stdout(CLOSE), stderr(CLOSE) if you
341 Options& closeOtherFds() { closeOtherFds_ = true; return *this; }
344 * Use the search path ($PATH) when searching for the executable.
346 Options& usePath() { usePath_ = true; return *this; }
349 * Change the child's working directory, after the vfork.
351 Options& chdir(const std::string& dir) { childDir_ = dir; return *this; }
355 * Child will receive a signal when the parent exits.
357 Options& parentDeathSignal(int sig) {
358 parentDeathSignal_ = sig;
364 * Child will be made a process group leader when it starts. Upside: one
365 * can reliably all its kill non-daemonizing descendants. Downside: the
366 * child will not receive Ctrl-C etc during interactive use.
368 Options& processGroupLeader() {
369 processGroupLeader_ = true;
374 * *** READ THIS WHOLE DOCBLOCK BEFORE USING ***
376 * Run this callback in the child after the fork, just before the
377 * exec(), and after the child's state has been completely set up:
378 * - signal handlers have been reset to default handling and unblocked
379 * - the working directory was set
380 * - closed any file descriptors specified via Options()
381 * - set child process flags (see code)
383 * This is EXTREMELY DANGEROUS. For example, this innocuous-looking code
384 * can cause a fraction of your Subprocess launches to hang forever:
386 * LOG(INFO) << "Hello from the child";
388 * The reason is that glog has an internal mutex. If your fork() happens
389 * when the parent has the mutex locked, the child will wait forever.
393 * - Be quick -- the parent thread is blocked until you exit.
394 * - Remember that other parent threads are running, and may mutate your
396 * - Avoid mutating any data belonging to the parent.
397 * - Avoid interacting with non-POD data that came from the parent.
398 * - Avoid any libraries that may internally reference non-POD state.
399 * - Especially beware parent mutexes, e.g. LOG() uses a global mutex.
400 * - Avoid invoking the parent's destructors (you can accidentally
401 * delete files, terminate network connections, etc).
402 * - Read http://ewontfix.com/7/
404 Options& dangerousPostForkPreExecCallback(
405 DangerousPostForkPreExecCallback* cob) {
406 dangerousPostForkPreExecCallback_ = cob;
412 * This is an experimental feature, it is best you don't use it at this
414 * Although folly would support cloning with custom flags in some form, this
415 * API might change in the near future. So use the following assuming it is
416 * experimental. (Apr 11, 2017)
418 * This unlocks Subprocess to support clone flags, many of them need
419 * CAP_SYS_ADMIN permissions. It might also require you to go through the
420 * implementation to understand what happens before, between and after the
423 * `man 2 clone` would be a starting point for knowing about the available
426 using clone_flags_t = uint64_t;
427 Options& useCloneWithFlags(clone_flags_t cloneFlags) noexcept {
428 cloneFlags_ = cloneFlags;
434 typedef boost::container::flat_map<int, int> FdMap;
436 bool closeOtherFds_{false};
437 bool usePath_{false};
438 std::string childDir_; // "" keeps the parent's working directory
440 int parentDeathSignal_{0};
442 bool processGroupLeader_{false};
443 DangerousPostForkPreExecCallback*
444 dangerousPostForkPreExecCallback_{nullptr};
446 // none means `vfork()` instead of a custom `clone()`
447 // Optional<> is used because value of '0' means do clone without any flags.
448 Optional<clone_flags_t> cloneFlags_;
452 // Non-copiable, but movable
453 Subprocess(const Subprocess&) = delete;
454 Subprocess& operator=(const Subprocess&) = delete;
455 Subprocess(Subprocess&&) = default;
456 Subprocess& operator=(Subprocess&&) = default;
459 * Create an uninitialized subprocess.
461 * In this state it can only be destroyed, or assigned to using the move
462 * assignment operator.
467 * Create a subprocess from the given arguments. argv[0] must be listed.
468 * If not-null, executable must be the actual executable
469 * being used (otherwise it's the same as argv[0]).
471 * If env is not-null, it must contain name=value strings to be used
472 * as the child's environment; otherwise, we inherit the environment
473 * from the parent. env must be null if options.usePath is set.
476 const std::vector<std::string>& argv,
477 const Options& options = Options(),
478 const char* executable = nullptr,
479 const std::vector<std::string>* env = nullptr);
483 * Create a subprocess run as a shell command (as shell -c 'command')
485 * The shell to use is taken from the environment variable $SHELL,
486 * or /bin/sh if $SHELL is unset.
488 FOLLY_DEPRECATED("Prefer not running in a shell or use `shellify`.")
490 const std::string& cmd,
491 const Options& options = Options(),
492 const std::vector<std::string>* env = nullptr);
495 //// The methods below only manipulate the process state, and do not
496 //// affect its communication pipes.
500 * Return the child's pid, or -1 if the child wasn't successfully spawned
501 * or has already been wait()ed upon.
506 * Return the child's status (as per wait()) if the process has already
507 * been waited on, -1 if the process is still running, or -2 if the
508 * process hasn't been successfully started. NOTE that this does not call
509 * waitpid() or Subprocess::poll(), but simply returns the status stored
510 * in the Subprocess object.
512 ProcessReturnCode returnCode() const { return returnCode_; }
515 * Poll the child's status and return it. Return the exit status if the
516 * subprocess had quit, or RUNNING otherwise. Throws an std::logic_error
517 * if called on a Subprocess whose status is no longer RUNNING. No other
518 * exceptions are possible. Aborts on egregious violations of contract,
519 * e.g. if you wait for the underlying process without going through this
520 * Subprocess instance.
522 ProcessReturnCode poll(struct rusage* ru = nullptr);
525 * Poll the child's status. If the process is still running, return false.
526 * Otherwise, return true if the process exited with status 0 (success),
527 * or throw CalledProcessError if the process exited with a non-zero status.
532 * Wait for the process to terminate and return its status. Like poll(),
533 * the only exception this can throw is std::logic_error if you call this
534 * on a Subprocess whose status is RUNNING. Aborts on egregious
535 * violations of contract, like an out-of-band waitpid(p.pid(), 0, 0).
537 ProcessReturnCode wait();
540 * Wait for the process to terminate, throw if unsuccessful.
545 * Send a signal to the child. Shortcuts for the commonly used Unix
548 void sendSignal(int signal);
549 void terminate() { sendSignal(SIGTERM); }
550 void kill() { sendSignal(SIGKILL); }
553 //// The methods below only affect the process's communication pipes, but
554 //// not its return code or state (they do not poll() or wait()).
558 * Communicate with the child until all pipes to/from the child are closed.
560 * The input buffer is written to the process' stdin pipe, and data is read
561 * from the stdout and stderr pipes. Non-blocking I/O is performed on all
562 * pipes simultaneously to avoid deadlocks.
564 * The stdin pipe will be closed after the full input buffer has been written.
565 * An error will be thrown if a non-empty input buffer is supplied but stdin
566 * was not configured as a pipe.
568 * Returns a pair of buffers containing the data read from stdout and stderr.
569 * If stdout or stderr is not a pipe, an empty IOBuf queue will be returned
570 * for the respective buffer.
572 * Note that communicate() and communicateIOBuf() both return when all
573 * pipes to/from the child are closed; the child might stay alive after
574 * that, so you must still wait().
576 * communicateIOBuf() uses IOBufQueue for buffering (which has the
577 * advantage that it won't try to allocate all data at once), but it does
578 * store the subprocess's entire output in memory before returning.
580 * communicate() uses strings for simplicity.
582 std::pair<IOBufQueue, IOBufQueue> communicateIOBuf(
583 IOBufQueue input = IOBufQueue());
585 std::pair<std::string, std::string> communicate(
586 StringPiece input = StringPiece());
589 * Communicate with the child until all pipes to/from the child are closed.
593 * readCallback(pfd, cfd) will be called whenever there's data available
594 * on any pipe *from* the child (PIPE_OUT). pfd is the file descriptor
595 * in the parent (that you use to read from); cfd is the file descriptor
596 * in the child (used for identifying the stream; 1 = child's standard
597 * output, 2 = child's standard error, etc)
599 * writeCallback(pfd, cfd) will be called whenever a pipe *to* the child is
600 * writable (PIPE_IN). pfd is the file descriptor in the parent (that you
601 * use to write to); cfd is the file descriptor in the child (used for
602 * identifying the stream; 0 = child's standard input, etc)
604 * The read and write callbacks must read from / write to pfd and return
605 * false during normal operation. Return true to tell communicate() to
606 * close the pipe. For readCallback, this might send SIGPIPE to the
607 * child, or make its writes fail with EPIPE, so you should generally
608 * avoid returning true unless you've reached end-of-file.
610 * communicate() returns when all pipes to/from the child are closed; the
611 * child might stay alive after that, so you must still wait().
612 * Conversely, the child may quit long before its pipes are closed, since
613 * its descendants can keep them alive forever.
615 * Most users won't need to use this callback version; the simpler version
616 * of communicate (which buffers data in memory) will probably work fine.
618 * == Things you must get correct ==
620 * 1) You MUST consume all data passed to readCallback (or return true to
621 * close the pipe). Similarly, you MUST write to a writable pipe (or
622 * return true to close the pipe). To do otherwise is an error that can
623 * result in a deadlock. You must do this even for pipes you are not
626 * 2) pfd is nonblocking, so be prepared for read() / write() to return -1
627 * and set errno to EAGAIN (in which case you should return false). Use
628 * readNoInt() from FileUtil.h to handle interrupted reads for you.
630 * 3) Your callbacks MUST NOT call any of the Subprocess methods that
631 * manipulate the pipe FDs. Check the docblocks, but, for example,
632 * neither closeParentFd (return true instead) nor takeOwnershipOfPipes
633 * are safe. Stick to reading/writing from pfd, as appropriate.
637 * 1) See ReadLinesCallback for an easy way to consume the child's output
638 * streams line-by-line (or tokenized by another delimiter).
640 * 2) "Wait until the descendants close the pipes" is usually the behavior
641 * you want, since the descendants may have something to say even if the
642 * immediate child is dead. If you need to be able to force-close all
643 * parent FDs, communicate() will NOT work for you. Do it your own way by
644 * using takeOwnershipOfPipes().
646 * Why not? You can return "true" from your callbacks to sever active
647 * pipes, but inactive ones can remain open indefinitely. It is
648 * impossible to safely close inactive pipes while another thread is
649 * blocked in communicate(). This is BY DESIGN. Racing communicate()'s
650 * read/write callbacks can result in wrong I/O and data corruption. This
651 * class would need internal synchronization and timeouts, a poor and
652 * expensive implementation choice, in order to make closeParentFd()
655 using FdCallback = folly::Function<bool(int, int)>;
656 void communicate(FdCallback readCallback, FdCallback writeCallback);
659 * A readCallback for Subprocess::communicate() that helps you consume
660 * lines (or other delimited pieces) from your subprocess's file
661 * descriptors. Use the readLinesCallback() helper to get template
662 * deduction. For example:
664 * subprocess.communicate(
665 * Subprocess::readLinesCallback(
666 * [](int fd, folly::StringPiece s) {
667 * std::cout << fd << " said: " << s;
668 * return false; // Keep reading from the child
671 * [](int pdf, int cfd){ return true; } // Don't write to the child
674 * If a file line exceeds maxLineLength, your callback will get some
675 * initial chunks of maxLineLength with no trailing delimiters. The final
676 * chunk of a line is delimiter-terminated iff the delimiter was present
677 * in the input. In particular, the last line in a file always lacks a
678 * delimiter -- so if a file ends on a delimiter, the final line is empty.
680 * Like a regular communicate() callback, your fdLineCb() normally returns
681 * false. It may return true to tell Subprocess to close the underlying
682 * file descriptor. The child process may then receive SIGPIPE or get
683 * EPIPE errors on writes.
685 template <class Callback>
686 class ReadLinesCallback {
688 // Binds an FD to the client-provided FD+line callback
689 struct StreamSplitterCallback {
690 StreamSplitterCallback(Callback& cb, int fd) : cb_(cb), fd_(fd) { }
691 // The return value semantics are inverted vs StreamSplitter
692 bool operator()(StringPiece s) { return !cb_(fd_, s); }
696 typedef gen::StreamSplitter<StreamSplitterCallback> LineSplitter;
698 explicit ReadLinesCallback(
700 uint64_t maxLineLength = 0, // No line length limit by default
701 char delimiter = '\n',
702 uint64_t bufSize = 1024
703 ) : fdLineCb_(std::forward<Callback>(fdLineCb)),
704 maxLineLength_(maxLineLength),
705 delimiter_(delimiter),
708 bool operator()(int pfd, int cfd) {
709 // Make a splitter for this cfd if it doesn't already exist
710 auto it = fdToSplitter_.find(cfd);
711 auto& splitter = (it != fdToSplitter_.end()) ? it->second
712 : fdToSplitter_.emplace(cfd, LineSplitter(
713 delimiter_, StreamSplitterCallback(fdLineCb_, cfd), maxLineLength_
715 // Read as much as we can from this FD
718 ssize_t ret = readNoInt(pfd, buf, bufSize_);
719 if (ret == -1 && errno == EAGAIN) { // No more data for now
722 checkUnixError(ret, "read");
723 if (ret == 0) { // Reached end-of-file
724 splitter.flush(); // Ignore return since the file is over anyway
727 if (!splitter(StringPiece(buf, ret))) {
728 return true; // The callback told us to stop
735 const uint64_t maxLineLength_;
736 const char delimiter_;
737 const uint64_t bufSize_;
738 // We lazily make splitters for all cfds that get used.
739 std::unordered_map<int, LineSplitter> fdToSplitter_;
742 // Helper to enable template deduction
743 template <class Callback>
744 static auto readLinesCallback(
746 uint64_t maxLineLength = 0, // No line length limit by default
747 char delimiter = '\n',
748 uint64_t bufSize = 1024)
749 -> ReadLinesCallback<typename std::decay<Callback>::type> {
750 return ReadLinesCallback<typename std::decay<Callback>::type>(
751 std::forward<Callback>(fdLineCb), maxLineLength, delimiter, bufSize);
755 * communicate() callbacks can use this to temporarily enable/disable
756 * notifications (callbacks) for a pipe to/from the child. By default,
757 * all are enabled. Useful for "chatty" communication -- you want to
758 * disable write callbacks until you receive the expected message.
760 * Disabling a pipe does not free you from the requirement to consume all
761 * incoming data. Failing to do so will easily create deadlock bugs.
763 * Throws if the childFd is not known.
765 void enableNotifications(int childFd, bool enabled);
768 * Are notifications for one pipe to/from child enabled? Throws if the
769 * childFd is not known.
771 bool notificationsEnabled(int childFd) const;
774 //// The following methods are meant for the cases when communicate() is
775 //// not suitable. You should not need them when you call communicate(),
776 //// and, in fact, it is INHERENTLY UNSAFE to use closeParentFd() or
777 //// takeOwnershipOfPipes() from a communicate() callback.
781 * Close the parent file descriptor given a file descriptor in the child.
782 * DO NOT USE from communicate() callbacks; make them return true instead.
784 void closeParentFd(int childFd);
787 * Set all pipes from / to child to be non-blocking. communicate() does
790 void setAllNonBlocking();
793 * Get parent file descriptor corresponding to the given file descriptor
794 * in the child. Throws if childFd isn't a pipe (PIPE_IN / PIPE_OUT).
795 * Do not close() the returned file descriptor; use closeParentFd, above.
797 int parentFd(int childFd) const {
798 return pipes_[findByChildFd(childFd)].pipe.fd();
800 int stdinFd() const { return parentFd(0); }
801 int stdoutFd() const { return parentFd(1); }
802 int stderrFd() const { return parentFd(2); }
805 * The child's pipes are logically separate from the process metadata
806 * (they may even be kept alive by the child's descendants). This call
807 * lets you manage the pipes' lifetime separetely from the lifetime of the
810 * After this call, the Subprocess instance will have no knowledge of
811 * these pipes, and the caller assumes responsibility for managing their
812 * lifetimes. Pro-tip: prefer to explicitly close() the pipes, since
813 * folly::File would otherwise silently suppress I/O errors.
815 * No, you may NOT call this from a communicate() callback.
818 ChildPipe(int fd, folly::File&& ppe) : childFd(fd), pipe(std::move(ppe)) {}
820 folly::File pipe; // Owns the parent FD
822 std::vector<ChildPipe> takeOwnershipOfPipes();
825 // spawn() sets up a pipe to read errors from the child,
826 // then calls spawnInternal() to do the bulk of the work. Once
827 // spawnInternal() returns it reads the error pipe to see if the child
828 // encountered any errors.
830 std::unique_ptr<const char*[]> argv,
831 const char* executable,
832 const Options& options,
833 const std::vector<std::string>* env);
835 std::unique_ptr<const char*[]> argv,
836 const char* executable,
838 const std::vector<std::string>* env,
841 // Actions to run in child.
842 // Note that this runs after vfork(), so tread lightly.
843 // Returns 0 on success, or an errno value on failure.
844 int prepareChild(const Options& options,
845 const sigset_t* sigmask,
846 const char* childDir) const;
847 int runChild(const char* executable, char** argv, char** env,
848 const Options& options) const;
851 * Read from the error pipe, and throw SubprocessSpawnError if the child
852 * failed before calling exec().
854 void readChildErrorPipe(int pfd, const char* executable);
856 // Returns an index into pipes_. Throws std::invalid_argument if not found.
857 size_t findByChildFd(const int childFd) const;
860 ProcessReturnCode returnCode_;
863 * Represents a pipe between this process, and the child process (or its
864 * descendant). To interact with these pipes, you can use communicate(),
865 * or use parentFd() and related methods, or separate them from the
866 * Subprocess instance entirely via takeOwnershipOfPipes().
868 struct Pipe : private boost::totally_ordered<Pipe> {
869 folly::File pipe; // Our end of the pipe, wrapped in a File to auto-close.
870 int childFd = -1; // Identifies the pipe: what FD is this in the child?
871 int direction = PIPE_IN; // one of PIPE_IN / PIPE_OUT
872 bool enabled = true; // Are notifications enabled in communicate()?
874 bool operator<(const Pipe& other) const {
875 return childFd < other.childFd;
877 bool operator==(const Pipe& other) const {
878 return childFd == other.childFd;
882 // Populated at process start according to fdActions, empty after
883 // takeOwnershipOfPipes(). Sorted by childFd. Can only have elements
884 // erased, but not inserted, after being populated.
886 // The number of pipes between parent and child is assumed to be small,
887 // so we're happy with a vector here, even if it means linear erase.
888 std::vector<Pipe> pipes_;