GPU: Make shader cache clearing backend independent

Parallel shader compilation introduced `GPU_shader_cache_dir_clear_old`.
The implementation was specific to OpenGL and could not be overwritten
by other backends. This PR improves the implementation so the backend
can have its own implementation.

This is needed for upcoming changes to the Vulkan backend where we
want to use similar mechanisms to speed up shader compilation and caching.

Pull Request: https://projects.blender.org/blender/blender/pulls/127680

source/blender/gpu/GPU_compilation_subprocess.hh

@@ -10,6 +10,4 @@
 
 void GPU_compilation_subprocess_run(const char *subprocess_name);
 
-void GPU_shader_cache_dir_clear_old();
-
 #endif

source/blender/gpu/GPU_shader.hh

@@ -388,6 +388,8 @@ int GPU_shader_get_builtin_uniform(GPUShader *shader, int builtin);
  */
 void GPU_shader_compile_static();
 
+void GPU_shader_cache_dir_clear_old();
+
 /** DEPRECATED: Use hard-coded buffer location instead. */
 enum GPUUniformBlockBuiltin {
   GPU_UNIFORM_BLOCK_VIEW = 0, /* viewBlock */

source/blender/gpu/dummy/dummy_backend.hh

@@ -93,6 +93,7 @@ class DummyBackend : public GPUBackend {
   {
     return new DummyVertexBuffer;
   }
+  void shader_cache_dir_clear_old() override {}
   void render_begin() override {}
   void render_end() override {}
   void render_step() override {}

source/blender/gpu/intern/gpu_backend.hh

@@ -55,6 +55,7 @@ class GPUBackend {
   virtual UniformBuf *uniformbuf_alloc(size_t size, const char *name) = 0;
   virtual StorageBuf *storagebuf_alloc(size_t size, GPUUsageType usage, const char *name) = 0;
   virtual VertBuf *vertbuf_alloc() = 0;
+  virtual void shader_cache_dir_clear_old() = 0;
 
   /* Render Frame Coordination --
    * Used for performing per-frame actions globally */

source/blender/gpu/intern/gpu_shader.cc

@@ -352,6 +352,11 @@ void GPU_shader_compile_static()
   gpu_shader_create_info_compile("");
 }
 
+void GPU_shader_cache_dir_clear_old()
+{
+  GPUBackend::get()->shader_cache_dir_clear_old();
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */

source/blender/gpu/metal/mtl_backend.hh

@@ -71,6 +71,7 @@ class MTLBackend : public GPUBackend {
   UniformBuf *uniformbuf_alloc(size_t size, const char *name) override;
   StorageBuf *storagebuf_alloc(size_t size, GPUUsageType usage, const char *name) override;
   VertBuf *vertbuf_alloc() override;
+  void shader_cache_dir_clear_old() override {}
 
   /* Render Frame Coordination. */
   void render_begin() override;

source/blender/gpu/opengl/gl_backend.hh

@@ -17,6 +17,7 @@
 #endif
 
 #include "gl_batch.hh"
+#include "gl_compilation_subprocess.hh"
 #include "gl_compute.hh"
 #include "gl_context.hh"
 #include "gl_drawlist.hh"
@@ -165,6 +166,13 @@ class GLBackend : public GPUBackend {
     glBindBuffer(GL_DISPATCH_INDIRECT_BUFFER, 0);
   }
 
+  void shader_cache_dir_clear_old() override
+  {
+#if BLI_SUBPROCESS_SUPPORT
+    GL_shader_cache_dir_clear_old();
+#endif
+  }
+
   /* Render Frame Coordination */
   void render_begin() override{};
   void render_end() override{};

source/blender/gpu/opengl/gl_compilation_subprocess.cc

@@ -283,7 +283,8 @@ void GPU_compilation_subprocess_run(const char *subprocess_name)
   GHOST_DisposeSystem(ghost_system);
 }
 
-void GPU_shader_cache_dir_clear_old()
+namespace blender::gpu {
+void GL_shader_cache_dir_clear_old()
 {
   std::string cache_dir = cache_dir_get();
 
@@ -302,5 +303,6 @@ void GPU_shader_cache_dir_clear_old()
   }
   BLI_filelist_free(entries, dir_len);
 }
+}  // namespace blender::gpu
 
 #endif

source/blender/gpu/opengl/gl_compilation_subprocess.hh

@@ -40,6 +40,8 @@ struct ShaderBinaryHeader {
 static_assert(sizeof(ShaderBinaryHeader) == compilation_subprocess_shared_memory_size,
               "Size must match the shared memory size");
 
+void GL_shader_cache_dir_clear_old();
+
 }  // namespace blender::gpu
 
 #endif

source/blender/gpu/vulkan/vk_backend.hh

@@ -76,6 +76,8 @@ class VKBackend : public GPUBackend {
   StorageBuf *storagebuf_alloc(size_t size, GPUUsageType usage, const char *name) override;
   VertBuf *vertbuf_alloc() override;
 
+  void shader_cache_dir_clear_old() override {}
+
   /* Render Frame Coordination --
    * Used for performing per-frame actions globally */
   void render_begin() override;

source/blender/windowmanager/intern/wm_init_exit.cc

@@ -656,6 +656,7 @@ void WM_exit_ex(bContext *C, const bool do_python_exit, const bool do_user_exit_
     DRW_gpu_context_enable_ex(false);
     UI_exit();
     GPU_pass_cache_free();
+    GPU_shader_cache_dir_clear_old();
     GPU_exit();
     DRW_gpu_context_disable_ex(false);
     DRW_gpu_context_destroy();
@@ -691,10 +692,6 @@ void WM_exit_ex(bContext *C, const bool do_python_exit, const bool do_user_exit_
 
   BKE_tempdir_session_purge();
 
-#if defined(WITH_OPENGL_BACKEND) && BLI_SUBPROCESS_SUPPORT
-  GPU_shader_cache_dir_clear_old();
-#endif
-
   /* Logging cannot be called after exiting (#CLOG_INFO, #CLOG_WARN etc will crash).
    * So postpone exiting until other sub-systems that may use logging have shut down. */
   CLG_exit();