backport fixes from pr #2178

* add in locked version of mono_domain_foreach
* add in unity prefix to new mutex and commented intended use case
* name update

Author: kkukshtel-unity

mono/metadata/appdomain.c

@@ -3312,9 +3312,13 @@ deregister_reflection_info_roots (MonoDomain *domain)
 	mono_domain_assemblies_unlock (domain);
 }
 
+extern MonoCoopMutex mono_domain_unload_mutex;
+
 static gsize WINAPI
 unload_thread_main (void *arg)
 {
+	mono_coop_mutex_lock(&mono_domain_unload_mutex);
+
 	unload_data *data = (unload_data*)arg;
 	MonoDomain *domain = data->domain;
 	MonoMemoryManager *memory_manager = mono_domain_memory_manager (domain);
@@ -3386,6 +3390,7 @@ unload_thread_main (void *arg)
 
 	result = 0; // success
 exit:
+	mono_coop_mutex_unlock(&mono_domain_unload_mutex);
 	mono_atomic_store_release (&data->done, TRUE);
 	unload_data_unref (data);
 	return result;

mono/metadata/appdomain.h

@@ -109,6 +109,9 @@ mono_domain_jit_foreach (MonoDomain *domain, MonoJitInfoFunc func, void *user_da
 MONO_API void
 mono_domain_foreach        (MonoDomainFunc func, void* user_data);
 
+MONO_API void
+mono_unity_domain_foreach_locked (MonoDomainFunc func, void* user_data);
+
 MONO_API void
 mono_domain_assembly_foreach (MonoDomain* domain, MonoDomainAssemblyFunc func, void* user_data);
 

mono/metadata/domain.c

@@ -86,6 +86,12 @@ gboolean mono_dont_free_domains;
 #define mono_appdomains_unlock() mono_coop_mutex_unlock (&appdomains_mutex)
 static MonoCoopMutex appdomains_mutex;
 
+/* Lock used to prevent domain enumeration while domains may be unloading.
+ * This lock must be taken before any other domain-related locks to prevent deadlock. 
+ * See https://github.com/Unity-Technologies/mono/pull/2173
+ */
+MonoCoopMutex mono_domain_unload_mutex;
+
 static MonoDomain *mono_root_domain = NULL;
 
 /* some statistics */
@@ -559,6 +565,7 @@ mono_init_internal (const char *filename, const char *exe_filename, const char *
 	mono_thread_info_attach ();
 
 	mono_coop_mutex_init_recursive (&appdomains_mutex);
+	mono_coop_mutex_init_recursive(&mono_domain_unload_mutex);
 
 	mono_metadata_init ();
 	mono_images_init ();
@@ -925,6 +932,7 @@ mono_cleanup (void)
 	mono_metadata_cleanup ();
 
 	mono_coop_mutex_destroy (&appdomains_mutex);
+	mono_coop_mutex_destroy (&mono_domain_unload_mutex);
 
 	mono_w32process_cleanup ();
 	mono_w32file_cleanup ();
@@ -1041,6 +1049,14 @@ mono_domain_foreach (MonoDomainFunc func, gpointer user_data)
 	MONO_EXIT_GC_UNSAFE;
 }
 
+void
+mono_unity_domain_foreach_locked(MonoDomainFunc func, gpointer user_data)
+{
+	mono_coop_mutex_lock(&mono_domain_unload_mutex);
+	mono_domain_foreach(func, user_data);
+	mono_coop_mutex_unlock(&mono_domain_unload_mutex);
+}
+
 void
 mono_domain_ensure_entry_assembly (MonoDomain *domain, MonoAssembly *assembly)
 {

mono/metadata/etw-profiler.c

@@ -290,7 +290,7 @@ on_attach ()
 	memset (&enumerationData, 0, sizeof (enumerationData));
 
 	// Iterate through each domain
-	mono_domain_foreach (on_enumerate_domain, &enumerationData);
+	mono_unity_domain_foreach_locked (on_enumerate_domain, &enumerationData);
 
 	ETW_PROFILER_LOG_ARGS ("Finished enumerating JIT data. Found %d domains, %d assemblies, %d methods", enumerationData.mNumDomains, enumerationData.mNumAssemblies, enumerationData.mNumMethods);
 }