Add mutex lock in get_shader_rid()#118202
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Acquire material_mutex in CanvasItemMaterial::get_shader_rid() before accessing shader_map/current_key. Fixes godotengine#118151
Nintorch
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get_shader_rid()
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CanvasItemMaterial::get_shader_rid()accesses the staticshader_mapandcurrent_keywithout holdingmaterial_mutex, whileflush_changes()(idle callback) modifies both under the mutex via_update_shader(). When the rendering thread callsget_shader_rid()concurrently, it can read a stale key that was just erased from the map, causing a use-after-free crash.This is most easily triggered by rapidly toggling the Blend Mode property on a CanvasItemMaterial assigned to a GPUParticles2D node, but affects any CanvasItemMaterial during rendering.
The fix adds
MutexLock lock(material_mutex)toget_shader_rid(), matching the locking convention already used byflush_changes(),_queue_shader_change(), and~CanvasItemMaterial(). CanvasItemMaterial was the only material class missing this protection, BaseMaterial3D, ParticleProcessMaterial, and others all synchronize correctly.