172 lines
5.3 KiB
C
172 lines
5.3 KiB
C
/***********************license start***************
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* Copyright (c) 2003-2010 Cavium Inc. (support@cavium.com). All rights
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* reserved.
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*
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met:
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*
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* * Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following
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* disclaimer in the documentation and/or other materials provided
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* with the distribution.
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* * Neither the name of Cavium Inc. nor the names of
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* its contributors may be used to endorse or promote products
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* derived from this software without specific prior written
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* permission.
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* This Software, including technical data, may be subject to U.S. export control
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* laws, including the U.S. Export Administration Act and its associated
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* regulations, and may be subject to export or import regulations in other
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* countries.
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* TO THE MAXIMUM EXTENT PERMITTED BY LAW, THE SOFTWARE IS PROVIDED "AS IS"
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* AND WITH ALL FAULTS AND CAVIUM INC. MAKES NO PROMISES, REPRESENTATIONS OR
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* WARRANTIES, EITHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, WITH RESPECT TO
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* THE SOFTWARE, INCLUDING ITS CONDITION, ITS CONFORMITY TO ANY REPRESENTATION OR
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* DESCRIPTION, OR THE EXISTENCE OF ANY LATENT OR PATENT DEFECTS, AND CAVIUM
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* SPECIFICALLY DISCLAIMS ALL IMPLIED (IF ANY) WARRANTIES OF TITLE,
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* MERCHANTABILITY, NONINFRINGEMENT, FITNESS FOR A PARTICULAR PURPOSE, LACK OF
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* VIRUSES, ACCURACY OR COMPLETENESS, QUIET ENJOYMENT, QUIET POSSESSION OR
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* CORRESPONDENCE TO DESCRIPTION. THE ENTIRE RISK ARISING OUT OF USE OR
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* PERFORMANCE OF THE SOFTWARE LIES WITH YOU.
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***********************license end**************************************/
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/**
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* @file
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*
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* This file provides reader/writer locks.
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*
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* <hr>$Revision: 70030 $<hr>
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*
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*
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*/
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#ifndef __CVMX_RWLOCK_H__
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#define __CVMX_RWLOCK_H__
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/* include to get atomic compare and store */
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#include "cvmx-atomic.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* Flags for lock value in rw lock structure */
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#define CVMX_RWLOCK_WRITE_FLAG 0x1
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#define CVMX_RWLOCK_READ_INC 0x2
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/* Writer preference locks (wp). Can be starved by writers. When a writer
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* is waiting, no readers are given the lock until all writers are done.
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*/
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typedef struct
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{
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volatile uint32_t lock;
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volatile uint32_t write_req;
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volatile uint32_t write_comp;
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} cvmx_rwlock_wp_lock_t;
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/**
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* Initialize a reader/writer lock. This must be done
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* by a single core before used.
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*
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* @param lock pointer to rwlock structure
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*/
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static inline void cvmx_rwlock_wp_init(cvmx_rwlock_wp_lock_t *lock)
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{
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lock->lock = 0;
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lock->write_req = 0;
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lock->write_comp = 0;
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}
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/**
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* Perform a reader lock. If a writer is pending, this
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* will wait for that writer to complete before locking.
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*
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* NOTE: Each thread/process must only lock any rwlock
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* once, or else a deadlock may result.
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*
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* @param lock pointer to rwlock structure
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*/
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static inline void cvmx_rwlock_wp_read_lock(cvmx_rwlock_wp_lock_t *lock)
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{
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/* Wait for outstanding write requests to be serviced */
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while (lock->write_req != lock->write_comp)
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;
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/* Add ourselves to interested reader count */
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cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), CVMX_RWLOCK_READ_INC);
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/* Wait for writer to finish. No writer will start again
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** until after we are done since we have already incremented
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** the reader count
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*/
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while (lock->lock & CVMX_RWLOCK_WRITE_FLAG)
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;
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}
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/**
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* Perform a reader unlock.
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*
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* @param lock pointer to rwlock structure
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*/
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static inline void cvmx_rwlock_wp_read_unlock(cvmx_rwlock_wp_lock_t *lock)
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{
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/* Remove ourselves to reader count */
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cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), -CVMX_RWLOCK_READ_INC);
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}
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/**
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* Perform a writer lock. Any readers that attempt
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* to get a lock while there are any pending write locks
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* will wait until all writers have completed. Starvation
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* of readers by writers is possible and must be avoided
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* by the application.
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*
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* @param lock pointer to rwlock structure
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*/
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static inline void cvmx_rwlock_wp_write_lock(cvmx_rwlock_wp_lock_t *lock)
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{
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/* Get previous value of write requests */
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uint32_t prev_writers = ((uint32_t)cvmx_atomic_fetch_and_add32((int32_t *)&(lock->write_req), 1));
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/* Spin until our turn */
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while (prev_writers != lock->write_comp)
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;
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/* Spin until no other readers or writers, then set write flag */
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while (!cvmx_atomic_compare_and_store32((uint32_t *)&(lock->lock), 0, CVMX_RWLOCK_WRITE_FLAG))
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;
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}
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/**
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* Perform a writer unlock.
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*
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* @param lock pointer to rwlock structure
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*/
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static inline void cvmx_rwlock_wp_write_unlock(cvmx_rwlock_wp_lock_t *lock)
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{
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/* Remove our writer flag */
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CVMX_SYNCWS; /* Make sure all writes in protected region are visible before unlock */
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cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), -CVMX_RWLOCK_WRITE_FLAG);
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cvmx_atomic_add32_nosync((int32_t *)&(lock->write_comp), 1);
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CVMX_SYNCWS; /* push unlock writes out, but don't stall */
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}
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#ifdef __cplusplus
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}
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#endif
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#endif /* __CVMX_RWLOCK_H__ */
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