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/**
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* Redistribution of this file is permitted under the BSD two clause license.
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*
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* Copyright 2019, The George Washington University
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* Author: Phani Gadepalli, phanikishoreg@gwu.edu
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*/
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#ifndef DEQUE_H
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#define DEQUE_H
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/*
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* This was implemented by referring to:
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* https://github.com/cpp-taskflow/cpp-taskflow/blob/9c28ccec910346a9937c40db7bdb542262053f9c/taskflow/executor/workstealing.hpp
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*
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* which is based on the following papers:
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*
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* The work stealing queue described in the paper, "Dynamic Circular Work-stealing Deque," SPAA, 2015.
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* Only the queue owner can perform pop and push operations, while others can steal data from the queue.
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*
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* PPoPP implementation paper, "Correct and Efficient Work-Stealing for Weak Memory Models"
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* https://www.di.ens.fr/~zappa/readings/ppopp13.pdf
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*/
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/* TODO: Implement the ability to dynamically resize! Issue #89 */
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#define DEQUE_MAX_SZ (1 << 23)
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#define DEQUE_PROTOTYPE(name, type) \
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struct deque_##name { \
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type wrk[DEQUE_MAX_SZ]; \
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long size; \
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\
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volatile long top; \
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volatile long bottom; \
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}; \
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\
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static inline void deque_init_##name(struct deque_##name *q, size_t sz) \
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{ \
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memset(q, 0, sizeof(struct deque_##name)); \
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\
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if (sz) { \
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/* only for size with pow of 2 */ \
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/* assert((sz & (sz - 1)) == 0); */ \
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assert(sz <= DEQUE_MAX_SZ); \
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} else { \
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sz = DEQUE_MAX_SZ; \
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} \
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\
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q->size = sz; \
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} \
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\
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/* Use mutual exclusion locks around push/pop if multi-threaded. */ \
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static inline int deque_push_##name(struct deque_##name *q, type *w) \
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{ \
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long ct, cb; \
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\
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ct = q->top; \
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cb = q->bottom; \
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\
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/* nope, fixed size only */ \
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if (q->size - 1 < (cb - ct)) return -ENOSPC; \
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\
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q->wrk[cb] = *w; \
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__sync_synchronize(); \
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if (__sync_bool_compare_and_swap(&q->bottom, cb, cb + 1) == false) assert(0); \
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\
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return 0; \
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} \
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\
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/* Use mutual exclusion locks around push/pop if multi-threaded. */ \
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static inline int deque_pop_##name(struct deque_##name *q, type *w) \
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{ \
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long ct = 0, sz = 0; \
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long cb = q->bottom - 1; \
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int ret = 0; \
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\
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if (__sync_bool_compare_and_swap(&q->bottom, cb + 1, cb) == false) assert(0); \
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\
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ct = q->top; \
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sz = cb - ct; \
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if (sz < 0) { \
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if (__sync_bool_compare_and_swap(&q->bottom, cb, ct) == false) assert(0); \
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\
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return -ENOENT; \
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} \
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\
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*w = q->wrk[cb]; \
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if (sz > 0) return 0; \
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\
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ret = __sync_bool_compare_and_swap(&q->top, ct, ct + 1); \
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if (__sync_bool_compare_and_swap(&q->bottom, cb, ct + 1) == false) assert(0); \
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if (ret == false) { \
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*w = NULL; \
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return -ENOENT; \
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} \
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\
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return 0; \
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} \
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/** \
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* deque_steal \
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* @param deque \
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* @param w pointer to location to copy stolen type to \
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* @returns 0 if successful, -2 if empty, -11 if unable to perform atomic operation \
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*/ \
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static inline int deque_steal_##name(struct deque_##name *deque, type *w) \
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{ \
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long ct, cb; \
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\
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ct = deque->top; \
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cb = deque->bottom; \
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\
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/* Empty */ \
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if (ct >= cb) return -ENOENT; \
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\
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*w = deque->wrk[ct]; \
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if (__sync_bool_compare_and_swap(&deque->top, ct, ct + 1) == false) return -EAGAIN; \
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\
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return 0; \
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}
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#endif /* DEQUE_H */
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