Add a shared ResourcePool to share resources between EffectChains.

[movit] / resource_pool.h

diff --git a/resource_pool.h b/resource_pool.h
new file mode 100644 (file)
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+++ b/resource_pool.h
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+#ifndef _MOVIT_RESOURCE_POOL_H
+#define _MOVIT_RESOURCE_POOL_H 1
+
+// A ResourcePool governs resources that are shared between multiple EffectChains;
+// in particular, resources that might be expensive to acquire or hold. Thus,
+// if you have many EffectChains, hooking them up to the same ResourcePool is
+// probably a good idea.
+//
+// However, hooking an EffectChain to a ResourcePool extends the OpenGL context
+// demands (see effect_chain.h) to that of the ResourcePool; all chains must then
+// only be used in OpenGL contexts sharing resources with each other. This is
+// the reason why there isn't just one global ResourcePool singleton (although
+// most practical users will just want one).
+//
+// Thread-safety: All functions except the constructor and destructor can be
+// safely called from multiple threads at the same time, provided they have
+// separate (but sharing) OpenGL contexts.
+
+#include <list>
+#include <map>
+#include <string>
+#include <utility>
+#include <GL/glew.h>
+#include <pthread.h>
+
+class ResourcePool {
+public:
+       // program_freelist_max_length is how many compiled programs that are unused to keep
+       // around after they are no longer in use (in case another EffectChain
+       // wants that exact program later). Shaders are expensive to compile and do not
+       // need a lot of resources to keep around, so this should be a reasonable number.
+       ResourcePool(size_t program_freelist_max_length = 100);
+       ~ResourcePool();
+
+       // All remaining functions are intended for calls from EffectChain only.
+
+       // Compile the given vertex+fragment shader pair, or fetch an already
+       // compiled program from the cache if possible. Keeps ownership of the
+       // program; you must call release_glsl_program() instead of deleting it
+       // when you no longer want it.
+       GLuint compile_glsl_program(const std::string& vertex_shader, const std::string& fragment_shader);
+       void release_glsl_program(GLuint glsl_program_num);
+
+private:
+       // Delete the given program and both its shaders.
+       void delete_program(GLuint program_num);
+
+       // Protects all the other elements in the class.
+       pthread_mutex_t lock;
+
+       size_t program_freelist_max_length;
+               
+       // A mapping from vertex/fragment shader source strings to compiled program number.
+       std::map<std::pair<std::string, std::string>, GLuint> programs;
+
+       // A mapping from compiled program number to number of current users.
+       // Once this reaches zero, the program is taken out of this map and instead
+       // put on the freelist (after which it may be deleted).
+       std::map<GLuint, int> program_refcount;
+
+       // A mapping from program number to vertex and fragment shaders.
+       std::map<GLuint, std::pair<GLuint, GLuint> > program_shaders;
+
+       // A list of programs that are no longer in use, most recently freed first.
+       // Once this reaches <program_freelist_max_length>, 
+       std::list<GLuint> program_freelist;
+};
+
+#endif  // !defined(_MOVIT_RESOURCE_POOL_H)