mp.input: send buffer ids with logs to avoid race conditions

This commit modifies the log methods in mp.input to always send the id
of the latest `input.get()` request with log entries, and allows
manually specifying an id to use instead.

Previously, the log methods applied to whichever input request happened
to be open when the log message was received. Even when scripts used
these methods correctly, there was the risk of sending a log to the
wrong log buffer if the active input request changed while the log
message was in transit; a race condition.

Now an id for the log buffer is always sent, either the id of the latest
`input.get()` request (preventing data races between scripts), or
a manually specified id passed as an extra parameter to the log methods
(preventing data races between multiple requests in the same script).

A side effect of this change is that logs can now be sent to specific
log buffers at any time, regardless of the currently active input
request (or lack thereof). I have not explicitly documented this as I
don't know if it's something we want to encourage.

Author: CogentRedTester

DOCS/man/javascript.rst

@@ -202,11 +202,11 @@ string/boolean/number)
 
 ``mp.input.terminate([id])``
 
-``mp.input.log(message, style)``
+``mp.input.log(message, style, terminal_style [, id])``
 
-``mp.input.log_error(message)``
+``mp.input.log_error(message [, id])``
 
-``mp.input.set_log(log)``
+``mp.input.set_log(log [, id])``
 
 ``exit()`` (global)
 

DOCS/man/lua.rst

@@ -1012,21 +1012,32 @@ REPL.
             end,
         })
 
-``input.log(message, style, terminal_style)``
+``input.log(message, style, terminal_style [, id])``
     Add a line to the log buffer. ``style`` can contain additional ASS tags to
     apply to ``message``, and ``terminal_style`` can contain escape sequences
     that are used when the console is displayed in the terminal.
 
-``input.log_error(message)``
+    ``id`` is a string identifying the specific log buffer to write to, and
+    defaults to the ``id`` of the latest ``input.get()`` request.
+    This can be used to avoid race conditions for scripts that send multiple
+    input requests with different log buffers.
+
+``input.log_error(message [, id])``
     Helper to add a line to the log buffer with the same color as the one used
     for commands that error. Useful when the user submits invalid input.
+    
+    ``id`` is a string identifying the specific log buffer to write to, and
+    defaults to the ``id`` of the latest ``input.get()`` request.
 
-``input.set_log(log)``
-    Replace the entire log buffer.
+``input.set_log(log [, id])``
+    Replaces the entire log buffer with a new list of log entries.
 
     ``log`` is a table of strings, or tables with ``text``, ``style`` and
     ``terminal_style`` keys.
 
+    ``id`` is a string identifying the specific log buffer to overwrite, and
+    defaults to the ``id`` of the latest ``input.get()`` request.
+
     Example:
 
     ::

player/javascript/defaults.js

@@ -654,6 +654,7 @@ mp.options = { read_options: read_options };
 *  input
 *********************************************************************/
 var input_handle_counter = 1;
+var latest_id
 
 function register_event_handler(t) {
     var handler_id = "input-event/" + input_handle_counter;
@@ -682,41 +683,51 @@ function register_event_handler(t) {
     return handler_id;
 }
 
-mp.input = {
-    get: function(t) {
-        t.has_completions = t.complete !== undefined;
-        var handler_id = register_event_handler(t);
+function input_request(t) {
+    t.has_completions = t.complete !== undefined;
 
-        mp.commandv("script-message-to", "console", "get-input",
-                    mp.script_name, handler_id, JSON.stringify(t));
+    var handler_id = register_event_handler(t);
+    mp.commandv("script-message-to", "console", "get-input",
+                mp.script_name, handler_id, JSON.stringify(t));
 
-        return {
-            handler_id: handler_id
-        }
+    return {
+        handler_id: handler_id
+    }
+}
+
+mp.input = {
+    get: function(t) {
+        latest_id = t.id || mp.script_name + (t.prompt || "");
+        return input_request(t);
     },
     terminate: function (t) {
         mp.commandv("script-message-to", "console", "disable", JSON.stringify({
             script_name: mp.script_name,
             handler_id: t ? t.handler_id : undefined,
         }));
     },
-    log: function (message, style, terminal_style) {
+    log: function (message, style, terminal_style, log_id) {
         mp.commandv("script-message-to", "console", "log", JSON.stringify({
+                        log_id: log_id || latest_id,
                         text: message,
                         style: style,
                         terminal_style: terminal_style,
                    }));
     },
-    log_error: function (message) {
-        mp.commandv("script-message-to", "console", "log",
-                    JSON.stringify({ text: message, error: true }));
+    log_error: function (message, log_id) {
+        mp.commandv("script-message-to", "console", "log", JSON.stringify({
+                        log_id: log_id || latest_id,
+                        text: message,
+                        error: true
+                    }));
     },
-    set_log: function (log) {
+    set_log: function (log, log_id) {
+        if (!(log_id || latest_id)) return;
         mp.commandv("script-message-to", "console", "set-log",
-                    JSON.stringify(log));
+                    JSON.stringify(log), log_id || latest_id);
     }
 }
-mp.input.select = mp.input.get
+mp.input.select = input_request
 
 /**********************************************************************
  *  various

player/lua/console.lua

@@ -1743,8 +1743,14 @@ end)
 
 -- Add a line to the log buffer
 mp.register_script_message("log", function (message)
-    local log_buffer = log_buffers[id]
     message = utils.parse_json(message)
+    if not message.log_id then return end
+
+    if not log_buffers[message.log_id] then
+        log_buffers[message.log_id] = {}
+    end
+
+    local log_buffer = log_buffers[message.log_id]
 
     log_buffer[#log_buffer + 1] = {
         text = message.text,
@@ -1757,7 +1763,7 @@ mp.register_script_message("log", function (message)
         table.remove(log_buffer, 1)
     end
 
-    if not open then
+    if not open or message.log_id ~= id then
         return
     end
 
@@ -1773,9 +1779,10 @@ mp.register_script_message("log", function (message)
     end
 end)
 
-mp.register_script_message("set-log", function (log)
+mp.register_script_message("set-log", function (log, log_id)
+    if not log_id then return end
     log = utils.parse_json(log)
-    log_buffers[id] = {}
+    log_buffers[log_id] = {}
 
     for i = 1, #log do
         if type(log[i]) == "table" then
@@ -1792,7 +1799,9 @@ mp.register_script_message("set-log", function (log)
         end
     end
 
-    render()
+    if log_id == id then
+        render()
+    end
 end)
 
 mp.register_script_message("complete", function (message)

player/lua/input.lua

@@ -18,6 +18,7 @@ License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
 local utils = require "mp.utils"
 local input = {}
 local handle_counter = 1
+local latest_id
 
 local function get_non_callbacks(t)
     local non_callbacks = {}
@@ -59,7 +60,7 @@ local function register_event_handler(t)
     return handler_id
 end
 
-function input.get(t)
+local function input_request(t)
     t.has_completions = t.complete ~= nil
 
     local handler_id = register_event_handler(t)
@@ -71,7 +72,13 @@ function input.get(t)
     }
 end
 
-input.select = input.get
+function input.get(t)
+    -- input.select does not support log buffers, so cannot override the latest id.
+    latest_id = t.id or mp.get_script_name()..(t.prompt or "")
+    return input_request(t)
+end
+
+input.select = input_request
 
 function input.terminate(t)
     mp.commandv("script-message-to", "console", "disable", utils.format_json({
@@ -80,21 +87,27 @@ function input.terminate(t)
     }))
 end
 
-function input.log(message, style, terminal_style)
+function input.log(message, style, terminal_style, log_id)
     mp.commandv("script-message-to", "console", "log", utils.format_json({
+                   log_id = log_id or latest_id,
                    text = message,
                    style = style,
                    terminal_style = terminal_style,
                }))
 end
 
-function input.log_error(message)
-    mp.commandv("script-message-to", "console", "log",
-                 utils.format_json({ text = message, error = true }))
+function input.log_error(message, log_id)
+    mp.commandv("script-message-to", "console", "log", utils.format_json({
+                   log_id = log_id or latest_id,
+                   text = message,
+                   error = true
+                }))
 end
 
-function input.set_log(log)
-    mp.commandv("script-message-to", "console", "set-log", utils.format_json(log))
+function input.set_log(log, log_id)
+    if not log_id or latest_id then return end
+    mp.commandv("script-message-to", "console", "set-log",
+                   utils.format_json(log), log_id or latest_id)
 end
 
 return input