Gawain: manage GL buffer IDs in a thread-safe way

Needed because deps graph can destroy objects from any thread. We ran into the same problem & solved it in GPU_buffers.

Implemented in C++11 since it provides the needed machinery. The interface is in C like the rest of Gawain.

source/blender/gpu/CMakeLists.txt

@@ -70,6 +70,8 @@ set(SRC
 	gawain/attrib_binding.h
 	gawain/batch.c
 	gawain/batch.h
+	gawain/buffer_id.h
+	gawain/buffer_id.cpp
 	gawain/common.h
 	gawain/element.c
 	gawain/element.h

source/blender/gpu/gawain/buffer_id.cpp

@@ -0,0 +1,116 @@
+
+// Gawain buffer IDs
+//
+// This code is part of the Gawain library, with modifications
+// specific to integration with Blender.
+//
+// Copyright 2016 Mike Erwin
+//
+// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of
+// the MPL was not distributed with this file, You can obtain one at https://mozilla.org/MPL/2.0/.#include "buffer_id.h"
+
+#include "buffer_id.h"
+#include <mutex>
+#include <vector>
+
+#define ORPHAN_DEBUG 0
+
+#if ORPHAN_DEBUG
+	#include <cstdio>
+#endif
+
+static std::vector<GLuint> orphaned_buffer_ids;
+static std::vector<GLuint> orphaned_vao_ids;
+
+static std::mutex orphan_mutex;
+
+extern "C" {
+extern int BLI_thread_is_main(void); // Blender-specific function
+}
+
+static bool thread_is_main()
+	{
+	// "main" here means the GL context's thread
+	return BLI_thread_is_main();
+	}
+
+GLuint buffer_id_alloc()
+	{
+#if TRUST_NO_ONE
+	assert(thread_is_main());
+#endif
+
+	// delete orphaned IDs
+	orphan_mutex.lock();
+	if (!orphaned_buffer_ids.empty())
+		{
+		const auto orphaned_buffer_ct = (unsigned)orphaned_buffer_ids.size();
+#if ORPHAN_DEBUG
+		printf("deleting %u orphaned VBO%s\n", orphaned_buffer_ct, orphaned_buffer_ct == 1 ? "" : "s");
+#endif
+		glDeleteBuffers(orphaned_buffer_ct, orphaned_buffer_ids.data());
+		orphaned_buffer_ids.clear();
+		}
+	orphan_mutex.unlock();
+
+	GLuint new_buffer_id;
+	glGenBuffers(1, &new_buffer_id);
+	return new_buffer_id;
+	}
+
+void buffer_id_free(GLuint buffer_id)
+	{
+	if (thread_is_main())
+		glDeleteBuffers(1, &buffer_id);
+	else
+		{
+		// add this ID to the orphaned list
+		orphan_mutex.lock();
+#if ORPHAN_DEBUG
+		printf("orphaning VBO %u\n", buffer_id);
+#endif
+		orphaned_buffer_ids.emplace_back(buffer_id);
+		orphan_mutex.unlock();
+		}
+	}
+
+GLuint vao_id_alloc()
+	{
+#if TRUST_NO_ONE
+	assert(thread_is_main());
+#endif
+
+	GLuint new_vao_id;
+
+	// delete orphaned IDs
+	orphan_mutex.lock();
+	if (!orphaned_vao_ids.empty())
+		{
+		const auto orphaned_vao_ct = (unsigned)orphaned_vao_ids.size();
+#if ORPHAN_DEBUG
+		printf("deleting %u orphaned VAO%s\n", orphaned_vao_ct, orphaned_vao_ct == 1 ? "" : "s");
+#endif
+		glDeleteVertexArrays(orphaned_vao_ct, orphaned_vao_ids.data());
+		orphaned_vao_ids.clear();
+		}
+	orphan_mutex.unlock();
+
+	glGenVertexArrays(1, &new_vao_id);
+	return new_vao_id;
+	}
+
+void vao_id_free(GLuint vao_id)
+	{
+	if (thread_is_main())
+		glDeleteVertexArrays(1, &vao_id);
+	else
+		{
+		// add this ID to the orphaned list
+		orphan_mutex.lock();
+#if ORPHAN_DEBUG
+		printf("orphaning VAO %u\n", vao_id);
+#endif
+		orphaned_vao_ids.emplace_back(vao_id);
+		orphan_mutex.unlock();
+		}
+	}

source/blender/gpu/gawain/buffer_id.h

@@ -0,0 +1,34 @@
+
+// Gawain buffer IDs
+//
+// This code is part of the Gawain library, with modifications
+// specific to integration with Blender.
+//
+// Copyright 2016 Mike Erwin
+//
+// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of
+// the MPL was not distributed with this file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+#pragma once
+
+// Manage GL buffer IDs in a thread-safe way
+// Use these instead of glGenBuffers & its friends
+// - alloc must be called from main thread
+// - free can be called from any thread
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "common.h"
+
+GLuint buffer_id_alloc(void);
+void buffer_id_free(GLuint buffer_id);
+
+GLuint vao_id_alloc(void);
+void vao_id_free(GLuint vao_id);
+
+
+#ifdef __cplusplus
+}
+#endif