Implement notifyd-based notification strategy for universal variables

(OS X specific)

env_universal_common.cpp

@@ -46,6 +46,11 @@
 #include "env_universal_common.h"
 #include "path.h"
 
+#if __APPLE__
+#define FISH_NOTIFYD_AVAILABLE 1
+#include <notify.h>
+#endif
+
 /**
    Non-wide version of the set command
 */
@@ -1497,12 +1502,87 @@ class universal_notifier_shmem_poller_t : public universal_notifier_t
             return usec_per_sec / 3; //3 times a second
         }
     }
+};
+
+class universal_notifier_notifyd_t : public universal_notifier_t
+{
+    int notify_fd;
+    int token;
+    std::string name;
+
+    void setup_notifyd()
+    {
+#if FISH_NOTIFYD_AVAILABLE
+        // per notify(3), the user.uid.%d style is only accessible to processes with that uid
+        char local_name[256];
+        snprintf(local_name, sizeof local_name, "user.uid.%d.%ls.uvars",  getuid(), program_name ? program_name : L"fish");
+        name.assign(local_name);
+
+        uint32_t status = notify_register_file_descriptor(name.c_str(), &this->notify_fd, 0, &this->token);
+        if (status != NOTIFY_STATUS_OK)
+        {
+            fprintf(stderr, "Warning: notify_register_file_descriptor() failed with status %u. Universal variable notifications may not be received.", status);
+        }
+        if (this->notify_fd >= 0)
+        {
+            // Mark us for non-blocking reads, with CLO_EXEC
+            int flags = fcntl(this->notify_fd, F_GETFL, 0);
+            fcntl(this->notify_fd, F_SETFL, flags | O_NONBLOCK | FD_CLOEXEC);
+        }
+#endif
+    }
+
+public:
+    universal_notifier_notifyd_t() : notify_fd(-1), token(0)
+    {
+        setup_notifyd();
+    }
+
+    ~universal_notifier_notifyd_t()
+    {
+        if (token != 0)
+        {
+            notify_cancel(token);
+        }
+    }
+
+    int notification_fd()
+    {
+        return notify_fd;
+    }
 
+    void drain_notification_fd(int fd)
+    {
+        /* notifyd notifications come in as 32 bit values. We don't care about the value. We set ourselves as non-blocking, so just read until we can't read any more. */
+        assert(fd == notify_fd);
+        unsigned char buff[64];
+        ssize_t amt_read;
+        do
+        {
+            amt_read = read(notify_fd, buff, sizeof buff);
+
+        } while (amt_read == sizeof buff);
+    }
+
+    void post_notification()
+    {
+#if FISH_NOTIFYD_AVAILABLE
+        uint32_t status = notify_post(name.c_str());
+        if (status != NOTIFY_STATUS_OK)
+        {
+            fprintf(stderr, "Warning: notify_post() failed with status %u. Universal variable notifications may not be sent.", status);
+        }
+#endif
+    }
 };
 
 universal_notifier_t::notifier_strategy_t universal_notifier_t::resolve_default_strategy()
 {
+#if FISH_NOTIFYD_AVAILABLE
+    return strategy_notifyd;
+#else
     return strategy_shmem_polling;
+#endif
 }
 
 universal_notifier_t &universal_notifier_t::default_notifier()
@@ -1522,6 +1602,9 @@ universal_notifier_t *universal_notifier_t::new_notifier_for_strategy(universal_
         case strategy_shmem_polling:
             return new universal_notifier_shmem_poller_t();
 
+        case strategy_notifyd:
+            return new universal_notifier_notifyd_t();
+
         default:
             fprintf(stderr, "Unsupported strategy %d\n", strat);
             return NULL;
@@ -1561,3 +1644,6 @@ unsigned long universal_notifier_t::usec_delay_between_polls() const
     return 0;
 }
 
+void universal_notifier_t::drain_notification_fd(int fd)
+{
+}

env_universal_common.h

@@ -316,6 +316,9 @@ class universal_notifier_t
 
     /* Recommended delay between polls. A value of 0 means no polling required (so no timeout) */
     virtual unsigned long usec_delay_between_polls() const;
+
+    /* The notification_fd is readable; drain it */
+    virtual void drain_notification_fd(int fd);
 };
 
 std::string get_machine_identifier();

fish_tests.cpp

@@ -2240,8 +2240,35 @@ static void test_universal()
     putc('\n', stderr);
 }
 
+bool poll_notifier(universal_notifier_t *note)
+{
+    bool result = false;
+    if (note->needs_polling())
+    {
+        result = note->poll();
+    }
+    else
+    {
+        int fd = note->notification_fd();
+        if (fd > 0)
+        {
+            fd_set fds;
+            FD_ZERO(&fds);
+            FD_SET(fd, &fds);
+            struct timeval tv = {0, 0};
+            if (select(fd + 1, &fds, NULL, NULL, &tv) > 0 && FD_ISSET(fd, &fds))
+            {
+                note->drain_notification_fd(fd);
+                result = true;
+            }
+        }
+    }
+    return result;
+}
+
 static void test_notifiers_with_strategy(universal_notifier_t::notifier_strategy_t strategy)
 {
+    assert(strategy != universal_notifier_t::strategy_default);
     say(L"Testing universal notifiers with strategy %d", (int)strategy);
     universal_notifier_t *notifiers[16];
     size_t notifier_count = sizeof notifiers / sizeof *notifiers;
@@ -2255,40 +2282,46 @@ static void test_notifiers_with_strategy(universal_notifier_t::notifier_strategy
     // Nobody should poll yet
     for (size_t i=0; i < notifier_count; i++)
     {
-        if (notifiers[i]->poll())
+        if (poll_notifier(notifiers[i]))
         {
-            err(L"Universal varibale notifier poll() returned true before any changes, with strategy %d", (int)strategy);
+            err(L"Universal variable notifier polled true before any changes, with strategy %d", (int)strategy);
         }
     }
 
     // Tweak each notifier. Verify that others see it.
     for (size_t post_idx=0; post_idx < notifier_count; post_idx++)
     {
         notifiers[post_idx]->post_notification();
+
+        // notifyd requires a round trip to the notifyd server, which means we have to wait a little bit to receive it
+        // In practice, this seems to be enough
+        if (strategy != universal_notifier_t::strategy_shmem_polling)
+        {
+            usleep(1000000 / 25);
+        }
         for (size_t i=0; i < notifier_count; i++)
         {
-            // Skip the one who posted
+            // We aren't concerned with the one who posted
+            // Poll from it (to drain it), and then skip it
             if (i == post_idx)
             {
+                poll_notifier(notifiers[i]);
                 continue;
             }
 
-            if (notifiers[i]->needs_polling())
+            if (! poll_notifier(notifiers[i]))
             {
-                if (! notifiers[i]->poll())
-                {
-                    err(L"Universal varibale notifier poll() failed to notice changes, with strategy %d", (int)strategy);
-                }
+                err(L"Universal variable notifier polled failed to notice changes, with strategy %d", (int)strategy);
             }
         }
     }
 
     // Nobody should poll now
     for (size_t i=0; i < notifier_count; i++)
     {
-        if (notifiers[i]->poll())
+        if (poll_notifier(notifiers[i]))
         {
-            err(L"Universal varibale notifier poll() returned true after all changes, with strategy %d", (int)strategy);
+            err(L"Universal variable notifier polled true after all changes, with strategy %d", (int)strategy);
         }
     }
 
@@ -2303,6 +2336,9 @@ static void test_notifiers_with_strategy(universal_notifier_t::notifier_strategy
 static void test_universal_notifiers()
 {
     test_notifiers_with_strategy(universal_notifier_t::strategy_shmem_polling);
+#if __APPLE__
+    test_notifiers_with_strategy(universal_notifier_t::strategy_notifyd);
+#endif
 }
 
 class history_tests_t

input_common.cpp

@@ -116,7 +116,15 @@ static wint_t readb()
         /* Get our uvar notifier */
         universal_notifier_t &notifier = universal_notifier_t::default_notifier();
 
-        /* Get the suggested delay */
+        /* Get the notification fd (possibly none) */
+        int notifier_fd = notifier.notification_fd();
+        if (notifier_fd > 0)
+        {
+            FD_SET(notifier_fd, &fdset);
+            fd_max = maxi(fd_max, notifier_fd);
+        }
+
+        /* Get the suggested delay (possibly none) */
         struct timeval tv = {};
         const unsigned long usecs_delay = notifier.usec_delay_between_polls();
         if (usecs_delay > 0)
@@ -180,9 +188,15 @@ static wint_t readb()
                 }
             }
 
+            /* Notifiers either poll or have an fd, not both. So at most one of these branches will be taken. */
             if (notifier.poll())
             {
-                fprintf(stderr, "Change note\n");
+                env_universal_barrier();
+            }
+
+            if (notifier_fd > 0 && FD_ISSET(notifier_fd, &fdset))
+            {
+                notifier.drain_notification_fd(notifier_fd);
                 env_universal_barrier();
             }