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Current File : //sys/contrib/octeon-sdk/cvmx-rwlock.h |
/***********************license start*************** * Copyright (c) 2003-2010 Cavium Networks (support@cavium.com). All rights * reserved. * * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are * met: * * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * * 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. * * Neither the name of Cavium Networks nor the names of * its contributors may be used to endorse or promote products * derived from this software without specific prior written * permission. * This Software, including technical data, may be subject to U.S. export control * laws, including the U.S. Export Administration Act and its associated * regulations, and may be subject to export or import regulations in other * countries. * TO THE MAXIMUM EXTENT PERMITTED BY LAW, THE SOFTWARE IS PROVIDED "AS IS" * AND WITH ALL FAULTS AND CAVIUM NETWORKS MAKES NO PROMISES, REPRESENTATIONS OR * WARRANTIES, EITHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, WITH RESPECT TO * THE SOFTWARE, INCLUDING ITS CONDITION, ITS CONFORMITY TO ANY REPRESENTATION OR * DESCRIPTION, OR THE EXISTENCE OF ANY LATENT OR PATENT DEFECTS, AND CAVIUM * SPECIFICALLY DISCLAIMS ALL IMPLIED (IF ANY) WARRANTIES OF TITLE, * MERCHANTABILITY, NONINFRINGEMENT, FITNESS FOR A PARTICULAR PURPOSE, LACK OF * VIRUSES, ACCURACY OR COMPLETENESS, QUIET ENJOYMENT, QUIET POSSESSION OR * CORRESPONDENCE TO DESCRIPTION. THE ENTIRE RISK ARISING OUT OF USE OR * PERFORMANCE OF THE SOFTWARE LIES WITH YOU. ***********************license end**************************************/ /** * @file * * This file provides reader/writer locks. * * <hr>$Revision: 49448 $<hr> * * */ #ifndef __CVMX_RWLOCK_H__ #define __CVMX_RWLOCK_H__ /* include to get atomic compare and store */ #include "cvmx-atomic.h" #ifdef __cplusplus extern "C" { #endif /* Flags for lock value in rw lock structure */ #define CVMX_RWLOCK_WRITE_FLAG 0x1 #define CVMX_RWLOCK_READ_INC 0x2 /* Writer preference locks (wp). Can be starved by writers. When a writer * is waiting, no readers are given the lock until all writers are done. */ typedef struct { volatile uint32_t lock; volatile uint32_t write_req; volatile uint32_t write_comp; } cvmx_rwlock_wp_lock_t; /** * Initialize a reader/writer lock. This must be done * by a single core before used. * * @param lock pointer to rwlock structure */ static inline void cvmx_rwlock_wp_init(cvmx_rwlock_wp_lock_t *lock) { lock->lock = 0; lock->write_req = 0; lock->write_comp = 0; } /** * Perform a reader lock. If a writer is pending, this * will wait for that writer to complete before locking. * * NOTE: Each thread/process must only lock any rwlock * once, or else a deadlock may result. * * @param lock pointer to rwlock structure */ static inline void cvmx_rwlock_wp_read_lock(cvmx_rwlock_wp_lock_t *lock) { /* Wait for outstanding write requests to be serviced */ while (lock->write_req != lock->write_comp) ; /* Add ourselves to interested reader count */ cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), CVMX_RWLOCK_READ_INC); /* Wait for writer to finish. No writer will start again ** until after we are done since we have already incremented ** the reader count */ while (lock->lock & CVMX_RWLOCK_WRITE_FLAG) ; } /** * Perform a reader unlock. * * @param lock pointer to rwlock structure */ static inline void cvmx_rwlock_wp_read_unlock(cvmx_rwlock_wp_lock_t *lock) { /* Remove ourselves to reader count */ cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), -CVMX_RWLOCK_READ_INC); } /** * Perform a writer lock. Any readers that attempt * to get a lock while there are any pending write locks * will wait until all writers have completed. Starvation * of readers by writers is possible and must be avoided * by the application. * * @param lock pointer to rwlock structure */ static inline void cvmx_rwlock_wp_write_lock(cvmx_rwlock_wp_lock_t *lock) { /* Get previous value of write requests */ uint32_t prev_writers = ((uint32_t)cvmx_atomic_fetch_and_add32((int32_t *)&(lock->write_req), 1)); /* Spin until our turn */ while (prev_writers != lock->write_comp) ; /* Spin until no other readers or writers, then set write flag */ while (!cvmx_atomic_compare_and_store32((uint32_t *)&(lock->lock), 0, CVMX_RWLOCK_WRITE_FLAG)) ; } /** * Perform a writer unlock. * * @param lock pointer to rwlock structure */ static inline void cvmx_rwlock_wp_write_unlock(cvmx_rwlock_wp_lock_t *lock) { /* Remove our writer flag */ CVMX_SYNCWS; /* Make sure all writes in protected region are visible before unlock */ cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), -CVMX_RWLOCK_WRITE_FLAG); cvmx_atomic_add32_nosync((int32_t *)&(lock->write_comp), 1); CVMX_SYNCWS; /* push unlock writes out, but don't stall */ } #ifdef __cplusplus } #endif #endif /* __CVMX_RWLOCK_H__ */