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Renderer: Reduce scope of mutex locks to prevent common deadlocks

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Fixes #102877
This commit is contained in:
Stuart Carnie 2025-04-08 15:17:04 +10:00
parent af2c713971
commit 09282c316a
6 changed files with 114 additions and 52 deletions
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89
scene/resources/material.cpp
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@ -684,28 +684,37 @@ void BaseMaterial3D::_update_shader() {
return; //no update required in the end
}
MutexLock lock(shader_map_mutex);
if (shader_map.has(current_key)) {
shader_map[current_key].users--;
if (shader_map[current_key].users == 0) {
// Deallocate shader which is no longer in use.
RS::get_singleton()->free(shader_map[current_key].shader);
shader_map.erase(current_key);
{
MutexLock lock(shader_map_mutex);
ShaderData *v = shader_map.getptr(current_key);
if (v) {
v->users--;
if (v->users == 0) {
// Deallocate shader which is no longer in use.
shader_rid = RID();
RS::get_singleton()->free(v->shader);
shader_map.erase(current_key);
}
}
current_key = mk;
v = shader_map.getptr(mk);
if (v) {
shader_rid = v->shader;
v->users++;
if (_get_material().is_valid()) {
RS::get_singleton()->material_set_shader(_get_material(), shader_rid);
}
return;
}
}
current_key = mk;
if (shader_map.has(mk)) {
shader_rid = shader_map[mk].shader;
shader_map[mk].users++;
if (_get_material().is_valid()) {
RS::get_singleton()->material_set_shader(_get_material(), shader_rid);
}
return;
}
// From this point, it is possible that multiple threads requesting the same key will
// race to create the shader. The winner, which is the one found in shader_map, will be
// used. The losers will free their shader.
String texfilter_str;
// Force linear filtering for the heightmap texture, as the heightmap effect
@ -1929,11 +1938,28 @@ void fragment() {)";
code += "}\n";
ShaderData shader_data;
shader_data.shader = RS::get_singleton()->shader_create_from_code(code);
shader_data.users = 1;
shader_map[mk] = shader_data;
shader_rid = shader_data.shader;
// We must create the shader outside the shader_map_mutex to avoid potential deadlocks with
// other tasks in the WorkerThreadPool simultaneously creating materials, which
// may also hold the shared shader_map_mutex lock.
RID new_shader = RS::get_singleton()->shader_create_from_code(code);
MutexLock lock(shader_map_mutex);
ShaderData *v = shader_map.getptr(mk);
if (unlikely(v)) {
// We raced and managed to create the same key concurrently, so we'll free the shader we just created,
// given we know it isn't used, and use the winner.
RS::get_singleton()->free(new_shader);
} else {
ShaderData shader_data;
shader_data.shader = new_shader;
// ShaderData will be inserted with a users count of 0, but we
// increment unconditionally outside this if block, whilst still under lock.
v = &shader_map.insert(mk, shader_data)->value;
}
shader_rid = v->shader;
v->users++;
if (_get_material().is_valid()) {
RS::get_singleton()->material_set_shader(_get_material(), shader_rid);
@ -1959,11 +1985,18 @@ void BaseMaterial3D::_check_material_rid() {
}
void BaseMaterial3D::flush_changes() {
MutexLock lock(material_mutex);
SelfList<BaseMaterial3D>::List copy;
{
MutexLock lock(material_mutex);
while (SelfList<BaseMaterial3D> *E = dirty_materials.first()) {
dirty_materials.remove(E);
copy.add(E);
}
}
while (dirty_materials.first()) {
dirty_materials.first()->self()->_update_shader();
dirty_materials.first()->remove_from_list();
while (SelfList<BaseMaterial3D> *E = copy.first()) {
E->self()->_update_shader();
copy.remove(E);
}
}