Reduce blocking

* Use `rpcnotify()`, rather than `rpcrequest()`, since none of our
  plugin opeerations use the return value.
* Plugin sends channel number to neovim as global variable.

Previously, we noticed that randomly, the plugin would write a request
to its output stream, but the plugin would not notice it. This was due
to the use of `rpcrequest()`. If neovim issued a (1) request to the
plugin, and the plugin tried to make a (2) request of neovim before
responding to request (1), neovim would ignore request (2), because it
was blocked. After receiving the response to request (1), and
unblocking, presumably request (2) was sitting in some IO buffer, and
would not be immediately read by neovim, causing delays.

Author: jebberjeb

plugin/socketrepl.vim

@@ -1,12 +1,12 @@
 let s:p_dir = expand('<sfile>:p:h')
 let g:is_running = 0
-let g:channel = -1
+let g:nvim_tcp_plugin_channel = 0
 
 function! StartIfNotRunning()
     if g:is_running == 0
         echo 'Starting SocketREPL client...'
         let jar_file_path = s:p_dir . '/../' . 'socket-repl-plugin-0.1.0-SNAPSHOT-standalone.jar'
-        let g:channel = rpcstart('stdbuf', ['--input=0', '--output=0', 'java', '-jar', jar_file_path])
+        call jobstart(['java', '-jar', jar_file_path], {'rpc': v:true})
         let g:is_running = 1
     endif
 endfunction
@@ -18,49 +18,45 @@ function! Connect(host_colon_port)
     else
         let conn = a:host_colon_port
     endif
-    let res = rpcrequest(g:channel, 'connect', conn)
+    let res = rpcnotify(g:nvim_tcp_plugin_channel, 'connect', conn)
     return res
 endfunction
 command! -nargs=? Connect call Connect("<args>")
 
 function! EvalBuffer()
     call StartIfNotRunning()
     ReplLog
-    let res = rpcrequest(g:channel, 'eval-buffer', [])
+    let res = rpcnotify(g:nvim_tcp_plugin_channel, 'eval-buffer', [])
     return res
 endfunction
 command! EvalBuffer call EvalBuffer()
 
 function! EvalCode()
     call StartIfNotRunning()
     ReplLog
-    let res = rpcrequest(g:channel, 'eval-code', [])
+    let res = rpcnotify(g:nvim_tcp_plugin_channel, 'eval-code', [])
     return res
 endfunction
 command! EvalCode call EvalCode()
 
 function! ReplLog(buffer_cmd)
     call StartIfNotRunning()
-    let res = rpcrequest(g:channel, 'show-log', a:buffer_cmd)
-    " Response to no-op will 'flush' plugin -> neovim message 'buffer'
-    call rpcrequest(g:channel, 'no-op', '')
+    let res = rpcnotify(g:nvim_tcp_plugin_channel, 'show-log', a:buffer_cmd)
     return res
 endfunction
 command! ReplLog call ReplLog(':botright new')
 
 function! DismissReplLog()
     call StartIfNotRunning()
-    let res = rpcrequest(g:channel, 'dismiss-log', [])
-    " Response to no-op will 'flush' plugin -> neovim message 'buffer'
-    call rpcrequest(g:channel, 'no-op', '')
+    let res = rpcnotify(g:nvim_tcp_plugin_channel, 'dismiss-log', [])
     return res
 endfunction
 command! DismissReplLog call DismissReplLog()
 
 function! Doc()
     call StartIfNotRunning()
     ReplLog
-    let res = rpcrequest(g:channel, 'doc', [])
+    let res = rpcnotify(g:nvim_tcp_plugin_channel, 'doc', [])
     return res
 endfunction
 command! Doc call Doc()