What: Merge the opal_free_list_t and ompi_free_list_t implementations and add explicit interfaces for single and multi-threaded use.
Why: Historically these two lists were different due to ompi_free_list_t dependencies in ompi (mpool). Those dependencies have since been moved to opal so it is safe to (finally) combine them. The combined free list comes in three flavors: - Single-threaded. Only to be used when it is guaranteed that no concurrent access will be made to the free list. Single-threaded functions are suffixed with _st. - Mutli-threaded. To be used when the free list may be accessed by multiple threads despite the setting of opal_using_threads. Multi-threaded functins are suffixed with _mt. - Conditionally multi-threaded. Common use case. These functions are thread-safe if opal_using_threads is set to true. Compatibility functions for the ompi_free_list_t and the old accessor functions (OPAL_FREE_LIST_*) are available while the code base is transitioned to the new class/functions. Additional changes to the free list: - Added a new argument to opal_free_list_init: mpool_reg_flags. These flags will be passed to the mpool allocation function for all free list allocations. - Free list item initializer functions now return an integer to indicate success or failure. This allows initializtion function that perform allocation to indicate whether the free list item is usable. If an initializer returns an error the item will not be added to the free list. Additionally, I took this opportunity to clean up the initialization functions. Instead of providing multiple flavors of initialization (ompi_free_list_init, ompi_free_list_init_new, ompi_free_list_init_ex, etc) there is only a single free list initializer: opal_free_list_init. On additional thought: some free list users store the opal_free_list_t their item belongs to in their opal_free_list_item_t subclass (ex. btl/sm/btl_sm_frag.h) so that the appropriate opal_free_list_t can be passed to opal_free_list_return. We could add an opal_free_list_t * to opal_free_list_item_t and change: void opal_free_list_return (opal_free_list_t *, opal_free_list_item_t *); to void opal_free_list_return (opal_free_list_item_t *); It would simplify some code with the cost of 8 bytes per free list item. If this is acceptable I can add the change to this RFC. When: Friday Mar 6. This gives me time to talk face-to-face with some of you at the MPI forum. PR: https://github.com/open-mpi/ompi/pull/407 -Nathan
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