Confirm channel is readable in event handler

src/MacVim/gui_macvim.m

@@ -2301,7 +2301,7 @@ gui_macvim_add_channel(channel_T *channel, ch_part_T part)
                                0,
                                dispatch_get_main_queue());
     dispatch_source_set_event_handler(s, ^{
-        channel_read(channel, part, "gui_macvim_add_channel");
+        channel_may_read(channel, part, "gui_macvim_add_channel");
     });
     dispatch_resume(s);
     return s;

src/channel.c

@@ -54,9 +54,7 @@
 # define fd_close(sd) close(sd)
 #endif
 
-#ifndef FEAT_GUI_MACVIM
 static void channel_read(channel_T *channel, ch_part_T part, char *func);
-#endif
 
 /* Whether a redraw is needed for appending a line to a buffer. */
 static int channel_need_redraw = FALSE;
@@ -3271,11 +3269,7 @@ channel_close_now(channel_T *channel)
  * "part" is PART_SOCK, PART_OUT or PART_ERR.
  * The data is put in the read queue.  No callbacks are invoked here.
  */
-#ifndef FEAT_GUI_MACVIM
     static void
-#else
-    void
-#endif
 channel_read(channel_T *channel, ch_part_T part, char *func)
 {
     static char_u	*buf = NULL;
@@ -3561,6 +3555,22 @@ theend:
     free_job_options(&opt);
 }
 
+# ifdef FEAT_GUI_MACVIM
+/*
+ * Read from channel "channel" in dispatch event handler.
+ * Channel may be already read out elsewhere before the handler invoked
+ * after an event arrived, so should be checked again.
+ */
+    void
+channel_may_read(channel_T *channel, ch_part_T part, char *func)
+{
+    sock_T	fd = channel->ch_part[part].ch_fd;
+
+    if (fd != INVALID_FD && channel_wait(channel, fd, 0) == CW_READY)
+	channel_read(channel, part, func);
+}
+# endif
+
 # if defined(WIN32) || defined(FEAT_GUI_X11) || defined(FEAT_GUI_GTK) \
 	|| defined(PROTO)
 /*

src/proto/channel.pro

@@ -33,6 +33,7 @@ void channel_clear(channel_T *channel);
 void channel_free_all(void);
 char_u *channel_read_block(channel_T *channel, ch_part_T part, int timeout);
 void common_channel_read(typval_T *argvars, typval_T *rettv, int raw);
+void channel_may_read(channel_T *channel, ch_part_T part, char *func);
 channel_T *channel_fd2channel(sock_T fd, ch_part_T *partp);
 void channel_handle_events(int only_keep_open);
 int channel_any_keep_open(void);
@@ -71,7 +72,4 @@ job_T *job_start(typval_T *argvars, jobopt_T *opt_arg);
 char *job_status(job_T *job);
 void job_info(job_T *job, dict_T *dict);
 int job_stop(job_T *job, typval_T *argvars, char *type);
-#ifdef FEAT_GUI_MACVIM
-void channel_read(channel_T *channel, ch_part_T part, char *func);
-#endif
 /* vim: set ft=c : */