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+/* POSIX-based operating system interface for GNU Make.
+Copyright (C) 2016 Free Software Foundation, Inc.
+This file is part of GNU Make.
+
+GNU Make is free software; you can redistribute it and/or modify it under the
+terms of the GNU General Public License as published by the Free Software
+Foundation; either version 3 of the License, or (at your option) any later
+version.
+
+GNU Make is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#include "makeint.h"
+
+#include <stdio.h>
+
+#ifdef HAVE_FCNTL_H
+# include <fcntl.h>
+#endif
+#if defined(HAVE_PSELECT) && defined(HAVE_SYS_SELECT_H)
+# include <sys/select.h>
+#endif
+
+#include "debug.h"
+#include "job.h"
+#include "os.h"
+
+#ifdef MAKE_JOBSERVER
+
+/* This section provides OS-specific functions to support the jobserver. */
+
+/* These track the state of the jobserver pipe. Passed to child instances. */
+static int job_fds[2] = { -1, -1 };
+
+/* Used to signal read() that a SIGCHLD happened. Always CLOEXEC.
+ If we use pselect() this will never be created and always -1.
+ */
+static int volatile job_rfd = -1; /* bird: added volatile to try ensure atomic update. */
+
+/* Token written to the pipe (could be any character...) */
+static char token = '+';
+
+static int
+make_job_rfd (void)
+{
+#ifdef HAVE_PSELECT
+ /* Pretend we succeeded. */
+ return 0;
+#else
+ /* bird: modified to use local variable and only update job_rfd once, otherwise
+ we're racing the signal handler clearing and closing this. */
+ int new_job_rfd;
+ EINTRLOOP (new_job_rfd, dup (job_fds[0]));
+ if (new_job_rfd >= 0)
+ CLOSE_ON_EXEC (new_job_rfd);
+
+ job_rfd = new_job_rfd;
+ return new_job_rfd;
+#endif
+}
+
+static void
+set_blocking (int fd, int blocking)
+{
+ // If we're not using pselect() don't change the blocking
+#ifdef HAVE_PSELECT
+ int flags;
+ EINTRLOOP (flags, fcntl (fd, F_GETFL));
+ if (flags >= 0)
+ {
+ int r;
+ flags = blocking ? (flags & ~O_NONBLOCK) : (flags | O_NONBLOCK);
+ EINTRLOOP (r, fcntl (fd, F_SETFL, flags));
+ if (r < 0)
+ pfatal_with_name ("fcntl(O_NONBLOCK)");
+ }
+#endif
+}
+
+unsigned int
+jobserver_setup (int slots)
+{
+ int r;
+
+ EINTRLOOP (r, pipe (job_fds));
+ if (r < 0)
+ pfatal_with_name (_("creating jobs pipe"));
+
+ if (make_job_rfd () < 0)
+ pfatal_with_name (_("duping jobs pipe"));
+
+ while (slots--)
+ {
+ EINTRLOOP (r, write (job_fds[1], &token, 1));
+ if (r != 1)
+ pfatal_with_name (_("init jobserver pipe"));
+ }
+
+ /* When using pselect() we want the read to be non-blocking. */
+ set_blocking (job_fds[0], 0);
+
+ return 1;
+}
+
+unsigned int
+jobserver_parse_auth (const char *auth)
+{
+ /* Given the command-line parameter, parse it. */
+ if (sscanf (auth, "%d,%d", &job_fds[0], &job_fds[1]) != 2)
+ OS (fatal, NILF,
+ _("internal error: invalid --jobserver-auth string '%s'"), auth);
+
+ DB (DB_JOBS,
+ (_("Jobserver client (fds %d,%d)\n"), job_fds[0], job_fds[1]));
+
+#ifdef HAVE_FCNTL_H
+# define FD_OK(_f) (fcntl ((_f), F_GETFD) != -1)
+#else
+# define FD_OK(_f) 1
+#endif
+
+ /* Make sure our pipeline is valid, and (possibly) create a duplicate pipe,
+ that will be closed in the SIGCHLD handler. If this fails with EBADF,
+ the parent has closed the pipe on us because it didn't think we were a
+ submake. If so, warn and default to -j1. */
+
+ if (!FD_OK (job_fds[0]) || !FD_OK (job_fds[1]) || make_job_rfd () < 0)
+ {
+ if (errno != EBADF)
+ pfatal_with_name (_("jobserver pipeline"));
+
+ job_fds[0] = job_fds[1] = -1;
+
+ return 0;
+ }
+
+ /* When using pselect() we want the read to be non-blocking. */
+ set_blocking (job_fds[0], 0);
+
+ return 1;
+}
+
+char *
+jobserver_get_auth (void)
+{
+ char *auth = xmalloc ((INTSTR_LENGTH * 2) + 2);
+ sprintf (auth, "%d,%d", job_fds[0], job_fds[1]);
+ return auth;
+}
+
+unsigned int
+jobserver_enabled (void)
+{
+ return job_fds[0] >= 0;
+}
+
+void
+jobserver_clear (void)
+{
+ if (job_fds[0] >= 0)
+ close (job_fds[0]);
+ if (job_fds[1] >= 0)
+ close (job_fds[1]);
+ if (job_rfd >= 0)
+ close (job_rfd);
+
+ job_fds[0] = job_fds[1] = job_rfd = -1;
+}
+
+void
+jobserver_release (int is_fatal)
+{
+ int r;
+ EINTRLOOP (r, write (job_fds[1], &token, 1));
+ if (r != 1)
+ {
+ if (is_fatal)
+ pfatal_with_name (_("write jobserver"));
+ perror_with_name ("write", "");
+ }
+}
+
+unsigned int
+jobserver_acquire_all (void)
+{
+ unsigned int tokens = 0;
+
+ /* Use blocking reads to wait for all outstanding jobs. */
+ set_blocking (job_fds[0], 1);
+
+ /* Close the write side, so the read() won't hang forever. */
+ close (job_fds[1]);
+ job_fds[1] = -1;
+
+ while (1)
+ {
+ char intake;
+ int r;
+ EINTRLOOP (r, read (job_fds[0], &intake, 1));
+ if (r != 1)
+ return tokens;
+ ++tokens;
+ }
+}
+
+/* Prepare the jobserver to start a child process. */
+void
+jobserver_pre_child (int recursive)
+{
+ /* If it's not a recursive make, avoid polutting the jobserver pipes. */
+ if (!recursive && job_fds[0] >= 0)
+ {
+ CLOSE_ON_EXEC (job_fds[0]);
+ CLOSE_ON_EXEC (job_fds[1]);
+ }
+}
+
+void
+jobserver_post_child (int recursive)
+{
+#if defined(F_GETFD) && defined(F_SETFD)
+ if (!recursive && job_fds[0] >= 0)
+ {
+ unsigned int i;
+ for (i = 0; i < 2; ++i)
+ {
+ int flags;
+ EINTRLOOP (flags, fcntl (job_fds[i], F_GETFD));
+ if (flags >= 0)
+ {
+ int r;
+ EINTRLOOP (r, fcntl (job_fds[i], F_SETFD, flags & ~FD_CLOEXEC));
+ }
+ }
+ }
+#endif
+}
+
+void
+jobserver_signal (void)
+{
+ if (job_rfd >= 0)
+ {
+ close (job_rfd);
+ job_rfd = -1;
+ }
+}
+
+void
+jobserver_pre_acquire (void)
+{
+ /* Make sure we have a dup'd FD. */
+ if (job_rfd < 0 && job_fds[0] >= 0 && make_job_rfd () < 0)
+ pfatal_with_name (_("duping jobs pipe"));
+}
+
+#ifdef HAVE_PSELECT
+
+/* Use pselect() to atomically wait for both a signal and a file descriptor.
+ It also provides a timeout facility so we don't need to use SIGALRM.
+
+ This method relies on the fact that SIGCHLD will be blocked everywhere,
+ and only unblocked (atomically) within the pselect() call, so we can
+ never miss a SIGCHLD.
+ */
+unsigned int
+jobserver_acquire (int timeout)
+{
+ struct timespec spec;
+ struct timespec *specp = NULL;
+ sigset_t empty;
+
+ sigemptyset (&empty);
+
+ if (timeout)
+ {
+ /* Alarm after one second (is this too granular?) */
+ spec.tv_sec = 1;
+ spec.tv_nsec = 0;
+ specp = &spec;
+ }
+
+ while (1)
+ {
+ fd_set readfds;
+ int r;
+ char intake;
+
+ FD_ZERO (&readfds);
+ FD_SET (job_fds[0], &readfds);
+
+ r = pselect (job_fds[0]+1, &readfds, NULL, NULL, specp, &empty);
+ if (r < 0)
+ switch (errno)
+ {
+ case EINTR:
+ /* SIGCHLD will show up as an EINTR. */
+ return 0;
+
+ case EBADF:
+ /* Someone closed the jobs pipe.
+ That shouldn't happen but if it does we're done. */
+ O (fatal, NILF, _("job server shut down"));
+
+ default:
+ pfatal_with_name (_("pselect jobs pipe"));
+ }
+
+ if (r == 0)
+ /* Timeout. */
+ return 0;
+
+ /* The read FD is ready: read it! This is non-blocking. */
+ EINTRLOOP (r, read (job_fds[0], &intake, 1));
+
+ if (r < 0)
+ {
+ /* Someone sniped our token! Try again. */
+ if (errno == EAGAIN)
+ continue;
+
+ pfatal_with_name (_("read jobs pipe"));
+ }
+
+ /* read() should never return 0: only the master make can reap all the
+ tokens and close the write side...?? */
+ return r > 0;
+ }
+}
+
+#else
+
+/* This method uses a "traditional" UNIX model for waiting on both a signal
+ and a file descriptor. However, it's complex and since we have a SIGCHLD
+ handler installed we need to check ALL system calls for EINTR: painful!
+
+ Read a token. As long as there's no token available we'll block. We
+ enable interruptible system calls before the read(2) so that if we get a
+ SIGCHLD while we're waiting, we'll return with EINTR and we can process the
+ death(s) and return tokens to the free pool.
+
+ Once we return from the read, we immediately reinstate restartable system
+ calls. This allows us to not worry about checking for EINTR on all the
+ other system calls in the program.
+
+ There is one other twist: there is a span between the time reap_children()
+ does its last check for dead children and the time the read(2) call is
+ entered, below, where if a child dies we won't notice. This is extremely
+ serious as it could cause us to deadlock, given the right set of events.
+
+ To avoid this, we do the following: before we reap_children(), we dup(2)
+ the read FD on the jobserver pipe. The read(2) call below uses that new
+ FD. In the signal handler, we close that FD. That way, if a child dies
+ during the section mentioned above, the read(2) will be invoked with an
+ invalid FD and will return immediately with EBADF. */
+
+static RETSIGTYPE
+job_noop (int sig UNUSED)
+{
+}
+
+/* Set the child handler action flags to FLAGS. */
+static void
+set_child_handler_action_flags (int set_handler, int set_alarm)
+{
+ struct sigaction sa;
+
+#ifdef __EMX__
+ /* The child handler must be turned off here. */
+ signal (SIGCHLD, SIG_DFL);
+#endif
+
+ memset (&sa, '\0', sizeof sa);
+ sa.sa_handler = child_handler;
+ sa.sa_flags = set_handler ? 0 : SA_RESTART;
+
+#if defined SIGCHLD
+ if (sigaction (SIGCHLD, &sa, NULL) < 0)
+ pfatal_with_name ("sigaction: SIGCHLD");
+#endif
+
+#if defined SIGCLD && SIGCLD != SIGCHLD
+ if (sigaction (SIGCLD, &sa, NULL) < 0)
+ pfatal_with_name ("sigaction: SIGCLD");
+#endif
+
+#if defined SIGALRM
+ if (set_alarm)
+ {
+ /* If we're about to enter the read(), set an alarm to wake up in a
+ second so we can check if the load has dropped and we can start more
+ work. On the way out, turn off the alarm and set SIG_DFL. */
+ if (set_handler)
+ {
+ sa.sa_handler = job_noop;
+ sa.sa_flags = 0;
+ if (sigaction (SIGALRM, &sa, NULL) < 0)
+ pfatal_with_name ("sigaction: SIGALRM");
+ alarm (1);
+ }
+ else
+ {
+ alarm (0);
+ sa.sa_handler = SIG_DFL;
+ sa.sa_flags = 0;
+ if (sigaction (SIGALRM, &sa, NULL) < 0)
+ pfatal_with_name ("sigaction: SIGALRM");
+ }
+ }
+#endif
+}
+
+unsigned int
+jobserver_acquire (int timeout)
+{
+ char intake;
+ int got_token;
+ int saved_errno;
+
+ /* Set interruptible system calls, and read() for a job token. */
+ set_child_handler_action_flags (1, timeout);
+
+ EINTRLOOP (got_token, read (job_rfd, &intake, 1));
+ saved_errno = errno;
+
+ set_child_handler_action_flags (0, timeout);
+
+ if (got_token == 1)
+ return 1;
+
+ /* If the error _wasn't_ expected (EINTR or EBADF), fatal. Otherwise,
+ go back and reap_children(), and try again. */
+ errno = saved_errno;
+
+ if (errno != EINTR && errno != EBADF)
+ pfatal_with_name (_("read jobs pipe"));
+
+ if (errno == EBADF)
+ DB (DB_JOBS, ("Read returned EBADF.\n"));
+
+ return 0;
+}
+
+#endif
+
+#endif /* MAKE_JOBSERVER */
+
+/* Create a "bad" file descriptor for stdin when parallel jobs are run. */
+int
+get_bad_stdin (void)
+{
+ static int bad_stdin = -1;
+
+ /* Set up a bad standard input that reads from a broken pipe. */
+
+ if (bad_stdin == -1)
+ {
+ /* Make a file descriptor that is the read end of a broken pipe.
+ This will be used for some children's standard inputs. */
+ int pd[2];
+ if (pipe (pd) == 0)
+ {
+ /* Close the write side. */
+ (void) close (pd[1]);
+ /* Save the read side. */
+ bad_stdin = pd[0];
+
+ /* Set the descriptor to close on exec, so it does not litter any
+ child's descriptor table. When it is dup2'd onto descriptor 0,
+ that descriptor will not close on exec. */
+ CLOSE_ON_EXEC (bad_stdin);
+ }
+ }
+
+ return bad_stdin;
+}
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