Terminate context in a child process of fork() to replace file descriptors to not interfere with parent process's context

src/ctx.cpp

@@ -49,6 +49,9 @@ zmq::ctx_t::ctx_t () :
     io_thread_count (ZMQ_IO_THREADS_DFLT),
     ipv6 (false)
 {
+#ifdef HAVE_FORK
+    pid = getpid();
+#endif
 }
 
 bool zmq::ctx_t::check_tag ()
@@ -89,6 +92,19 @@ int zmq::ctx_t::terminate ()
     slot_sync.lock ();
     if (!starting) {
 
+#ifdef HAVE_FORK
+        if (pid != getpid())
+        {
+            // we are a forked child process. Close all file descriptors
+            // inherited from the parent.
+            for (sockets_t::size_type i = 0; i != sockets.size (); i++)
+            {
+                sockets[i]->get_mailbox()->forked();
+            }
+
+            term_mailbox.forked();
+        }
+#endif
         //  Check whether termination was already underway, but interrupted and now
         //  restarted.
         bool restarted = terminating;

src/ctx.hpp

@@ -167,6 +167,11 @@ namespace zmq
 
         ctx_t (const ctx_t&);
         const ctx_t &operator = (const ctx_t&);
+
+#ifdef HAVE_FORK
+        // the process that created this context. Used to detect forking.
+        pid_t pid;
+#endif
     };
 
 }

src/kqueue.cpp

@@ -48,6 +48,9 @@ zmq::kqueue_t::kqueue_t () :
     //  Create event queue
     kqueue_fd = kqueue ();
     errno_assert (kqueue_fd != -1);
+#ifdef HAVE_FORK
+    pid = getpid();
+#endif
 }
 
 zmq::kqueue_t::~kqueue_t ()
@@ -161,6 +164,13 @@ void zmq::kqueue_t::loop ()
         timespec ts = {timeout / 1000, (timeout % 1000) * 1000000};
         int n = kevent (kqueue_fd, NULL, 0, &ev_buf [0], max_io_events,
             timeout ? &ts: NULL);
+#ifdef HAVE_FORK
+        if (unlikely(pid != getpid())) {
+            //printf("zmq::kqueue_t::loop aborting on forked child %d\n", (int)getpid());
+            // simply exit the loop in a forked process.
+            return;
+        }
+#endif
         if (n == -1) {
             errno_assert (errno == EINTR);
             continue;

src/kqueue.hpp

@@ -25,6 +25,7 @@
 #if defined ZMQ_USE_KQUEUE
 
 #include <vector>
+#include <unistd.h>
 
 #include "fd.hpp"
 #include "thread.hpp"
@@ -94,6 +95,11 @@ namespace zmq
 
         kqueue_t (const kqueue_t&);
         const kqueue_t &operator = (const kqueue_t&);
+
+#ifdef HAVE_FORK
+        // the process that created this context. Used to detect forking.
+        pid_t pid;
+#endif
     };
 
     typedef kqueue_t poller_t;

src/mailbox.cpp

@@ -82,4 +82,3 @@ int zmq::mailbox_t::recv (command_t *cmd_, int timeout_)
     zmq_assert (ok);
     return 0;
 }
-

src/mailbox.hpp

@@ -44,6 +44,13 @@ namespace zmq
         void send (const command_t &cmd_);
         int recv (command_t *cmd_, int timeout_);
         
+#ifdef HAVE_FORK
+        // close the file descriptors in the signaller. This is used in a forked
+        // child process to close the file descriptors so that they do not interfere
+        // with the context in the parent process.
+        void forked() { signaler.forked(); }
+#endif
+
     private:
 
         //  The pipe to store actual commands.

src/reaper.cpp

@@ -31,6 +31,10 @@ zmq::reaper_t::reaper_t (class ctx_t *ctx_, uint32_t tid_) :
 
     mailbox_handle = poller->add_fd (mailbox.get_fd (), this);
     poller->set_pollin (mailbox_handle);
+
+#ifdef HAVE_FORK
+    pid = getpid();
+#endif
 }
 
 zmq::reaper_t::~reaper_t ()
@@ -57,6 +61,13 @@ void zmq::reaper_t::stop ()
 void zmq::reaper_t::in_event ()
 {
     while (true) {
+#ifdef HAVE_FORK
+        if (unlikely(pid != getpid()))
+        {
+            //printf("zmq::reaper_t::in_event return in child process %d\n", (int)getpid());
+            return;
+        }
+#endif
 
         //  Get the next command. If there is none, exit.
         command_t cmd;

src/reaper.hpp

@@ -72,6 +72,11 @@ namespace zmq
 
         reaper_t (const reaper_t&);
         const reaper_t &operator = (const reaper_t&);
+
+#ifdef HAVE_FORK
+        // the process that created this context. Used to detect forking.
+        pid_t pid;
+#endif
     };
 
 }

src/signaler.cpp

@@ -86,6 +86,10 @@ zmq::signaler_t::signaler_t ()
     //  Set both fds to non-blocking mode.
     unblock_socket (w);
     unblock_socket (r);
+
+#ifdef HAVE_FORK
+    pid = getpid();
+#endif
 }
 
 zmq::signaler_t::~signaler_t ()
@@ -117,6 +121,12 @@ zmq::fd_t zmq::signaler_t::get_fd ()
 
 void zmq::signaler_t::send ()
 {
+#if HAVE_FORK
+    if (unlikely(pid != getpid())) {
+        //printf("Child process %d signaler_t::send returning without sending #1\n", getpid());
+        return; // do not send anything in forked child context
+    }
+#endif
 #if defined ZMQ_HAVE_EVENTFD
     const uint64_t inc = 1;
     ssize_t sz = write (w, &inc, sizeof (inc));
@@ -132,6 +142,13 @@ void zmq::signaler_t::send ()
         ssize_t nbytes = ::send (w, &dummy, sizeof (dummy), 0);
         if (unlikely (nbytes == -1 && errno == EINTR))
             continue;
+#if HAVE_FORK
+        if (unlikely(pid != getpid())) {
+            //printf("Child process %d signaler_t::send returning without sending #2\n", getpid());
+            errno = EINTR;
+            break;
+        }
+#endif
         zmq_assert (nbytes == sizeof (dummy));
         break;
     }
@@ -140,6 +157,17 @@ void zmq::signaler_t::send ()
 
 int zmq::signaler_t::wait (int timeout_)
 {
+#ifdef HAVE_FORK
+    if (unlikely(pid != getpid()))
+    {
+        // we have forked and the file descriptor is closed. Emulate an interupt
+        // response.
+        //printf("Child process %d signaler_t::wait returning simulating interrupt #1\n", getpid());
+        errno = EINTR;
+        return -1;
+    }
+#endif
+
 #ifdef ZMQ_SIGNALER_WAIT_BASED_ON_POLL
 
     struct pollfd pfd;
@@ -155,6 +183,16 @@ int zmq::signaler_t::wait (int timeout_)
         errno = EAGAIN;
         return -1;
     }
+#ifdef HAVE_FORK
+    if (unlikely(pid != getpid()))
+    {
+        // we have forked and the file descriptor is closed. Emulate an interupt
+        // response.
+        //printf("Child process %d signaler_t::wait returning simulating interrupt #2\n", getpid());
+        errno = EINTR;
+        return -1;
+    }
+#endif
     zmq_assert (rc == 1);
     zmq_assert (pfd.revents & POLLIN);
     return 0;
@@ -225,6 +263,30 @@ void zmq::signaler_t::recv ()
 #endif
 }
 
+#ifdef HAVE_FORK
+void zmq::signaler_t::forked()
+{
+    int oldr = r;
+    int oldw = w;
+
+    // replace the file descriptors created in the parent with new
+    // ones, and close the inherited ones
+    make_fdpair(&r, &w);
+#if defined ZMQ_HAVE_EVENTFD
+    int rc = close (oldr);
+    errno_assert (rc == 0);
+#else
+    int rc = close (oldw);
+    errno_assert (rc == 0);
+    rc = close (oldr);
+    errno_assert (rc == 0);
+#endif
+}
+#endif
+
+
+
+
 int zmq::signaler_t::make_fdpair (fd_t *r_, fd_t *w_)
 {
 #if defined ZMQ_HAVE_EVENTFD

src/signaler.hpp

@@ -20,6 +20,10 @@
 #ifndef __ZMQ_SIGNALER_HPP_INCLUDED__
 #define __ZMQ_SIGNALER_HPP_INCLUDED__
 
+#ifdef HAVE_FORK
+#include <unistd.h>
+#endif
+
 #include "fd.hpp"
 
 namespace zmq
@@ -41,7 +45,13 @@ namespace zmq
         void send ();
         int wait (int timeout_);
         void recv ();
-        
+
+#ifdef HAVE_FORK
+        // close the file descriptors in a forked child process so that they
+        // do not interfere with the context in the parent process.
+        void forked();
+#endif
+
     private:
 
         //  Creates a pair of filedescriptors that will be used
@@ -55,6 +65,14 @@ namespace zmq
         //  Disable copying of signaler_t object.
         signaler_t (const signaler_t&);
         const signaler_t &operator = (const signaler_t&);
+
+#ifdef HAVE_FORK
+        // the process that created this context. Used to detect forking.
+        pid_t pid;
+        // idempotent close of file descriptors that is safe to use by destructor
+        // and forked().
+        void close_internal();
+#endif
     };
 
 }