[gjs/ewlsh/fix-threading-with-logging: 26/26] gjs-util: Fallback to default log handler in other threads

[Evan Welsh <ewlsh src gnome org>]

commit 766bf1f3696870d15f3b16edb56549297b321255
Author: Evan Welsh <contact evanwelsh com>
Date:   Thu Jul 7 02:53:42 2022 -0400

    gjs-util: Fallback to default log handler in other threads
    
    JavaScript functions can't be called from other threads, to prevent
    this, store which thread the custom writer was originally set
    from and then fallback to the default log writer if another thread
    calls the handler. Also fallback to the default writer if the
    custom writer returns UNHANDLED.
    
    Fixes #481

 libgjs-private/gjs-util.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
---
diff --git a/libgjs-private/gjs-util.c b/libgjs-private/gjs-util.c
index d0e52b641..e18d99e62 100644
--- a/libgjs-private/gjs-util.c
+++ b/libgjs-private/gjs-util.c
@@ -318,11 +318,19 @@ void gjs_gtk_custom_sorter_set_sort_func(GObject* sorter,
 
 static void* log_writer_user_data = NULL;
 static GDestroyNotify log_writer_user_data_free = NULL;
+static GThread* log_writer_thread = NULL;
 
 static GLogWriterOutput gjs_log_writer_func_wrapper(GLogLevelFlags log_level,
                                                     const GLogField* fields,
                                                     size_t n_fields,
                                                     void* user_data) {
+    g_assert(log_writer_thread);
+
+    // If the wrapper is called from a thread other than the one that set it,
+    // return unhandled so the fallback logger is used.
+    if (g_thread_self() != log_writer_thread)
+        return g_log_writer_default(log_level, fields, n_fields, NULL);
+
     GjsGLogWriterFunc func = (GjsGLogWriterFunc)user_data;
     GVariantDict dict;
     g_variant_dict_init(&dict, NULL);
@@ -363,6 +371,12 @@ static GLogWriterOutput gjs_log_writer_func_wrapper(GLogLevelFlags log_level,
         func(log_level, string_fields, log_writer_user_data);
 
     g_variant_unref(string_fields);
+
+    // If the function did not handle the log, fallback to the default
+    // handler.
+    if (output == G_LOG_WRITER_UNHANDLED)
+        return g_log_writer_default(log_level, fields, n_fields, NULL);
+
     return output;
 }
 
@@ -379,6 +393,7 @@ void gjs_log_set_writer_default() {
     g_log_set_writer_func(g_log_writer_default, NULL, NULL);
     log_writer_user_data_free = NULL;
     log_writer_user_data = NULL;
+    log_writer_thread = NULL;
 }
 
 /**
@@ -395,6 +410,7 @@ void gjs_log_set_writer_func(GjsGLogWriterFunc func, void* user_data,
                              GDestroyNotify user_data_free) {
     log_writer_user_data = user_data;
     log_writer_user_data_free = user_data_free;
+    log_writer_thread = g_thread_self();
 
     g_log_set_writer_func(gjs_log_writer_func_wrapper, func, NULL);
 }