diff options
Diffstat (limited to 'include/ck_pflock.h')
| -rw-r--r-- | include/ck_pflock.h | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/include/ck_pflock.h b/include/ck_pflock.h new file mode 100644 index 0000000..61b42bd --- /dev/null +++ b/include/ck_pflock.h @@ -0,0 +1,142 @@ +/* + * Copyright 2013 John Wittrock. + * Copyright 2013-2015 Samy Al Bahra. + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +#ifndef CK_PFLOCK_H +#define CK_PFLOCK_H + +/* + * This is an implementation of phase-fair locks derived from the work + * described in: + * Brandenburg, B. and Anderson, J. 2010. Spin-Based + * Reader-Writer Synchronization for Multiprocessor Real-Time Systems + */ + +#include <ck_cc.h> +#include <ck_pr.h> + +struct ck_pflock { + uint32_t rin; + uint32_t rout; + uint32_t win; + uint32_t wout; +}; +typedef struct ck_pflock ck_pflock_t; + +#define CK_PFLOCK_LSB 0xFFFFFFF0 +#define CK_PFLOCK_RINC 0x100 /* Reader increment value. */ +#define CK_PFLOCK_WBITS 0x3 /* Writer bits in reader. */ +#define CK_PFLOCK_PRES 0x2 /* Writer present bit. */ +#define CK_PFLOCK_PHID 0x1 /* Phase ID bit. */ + +#define CK_PFLOCK_INITIALIZER {0, 0, 0, 0} + +CK_CC_INLINE static void +ck_pflock_init(struct ck_pflock *pf) +{ + + pf->rin = 0; + pf->rout = 0; + pf->win = 0; + pf->wout = 0; + ck_pr_barrier(); + + return; +} + +CK_CC_INLINE static void +ck_pflock_write_unlock(ck_pflock_t *pf) +{ + + ck_pr_fence_unlock(); + + /* Migrate from write phase to read phase. */ + ck_pr_and_32(&pf->rin, CK_PFLOCK_LSB); + + /* Allow other writers to continue. */ + ck_pr_faa_32(&pf->wout, 1); + return; +} + +CK_CC_INLINE static void +ck_pflock_write_lock(ck_pflock_t *pf) +{ + uint32_t ticket; + + /* Acquire ownership of write-phase. */ + ticket = ck_pr_faa_32(&pf->win, 1); + while (ck_pr_load_32(&pf->wout) != ticket) + ck_pr_stall(); + + /* + * Acquire ticket on read-side in order to allow them + * to flush. Indicates to any incoming reader that a + * write-phase is pending. + */ + ticket = ck_pr_faa_32(&pf->rin, + (ticket & CK_PFLOCK_PHID) | CK_PFLOCK_PRES); + + /* Wait for any pending readers to flush. */ + while (ck_pr_load_32(&pf->rout) != ticket) + ck_pr_stall(); + + ck_pr_fence_lock(); + return; +} + +CK_CC_INLINE static void +ck_pflock_read_unlock(ck_pflock_t *pf) +{ + + ck_pr_fence_unlock(); + ck_pr_faa_32(&pf->rout, CK_PFLOCK_RINC); + return; +} + +CK_CC_INLINE static void +ck_pflock_read_lock(ck_pflock_t *pf) +{ + uint32_t w; + + /* + * If no writer is present, then the operation has completed + * successfully. + */ + w = ck_pr_faa_32(&pf->rin, CK_PFLOCK_RINC) & CK_PFLOCK_WBITS; + if (w == 0) + goto leave; + + /* Wait for current write phase to complete. */ + while ((ck_pr_load_32(&pf->rin) & CK_PFLOCK_WBITS) == w) + ck_pr_stall(); + +leave: + /* Acquire semantics with respect to readers. */ + ck_pr_fence_lock(); + return; +} + +#endif /* CK_PFLOCK_H */ |