module/zfs/include/sys/rrwlock.h

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
  23  * Use is subject to license terms.
  24  */
  25
  26 #ifndef _SYS_RR_RW_LOCK_H
  27 #define _SYS_RR_RW_LOCK_H
  28
  29
  30
  31 #ifdef  __cplusplus
  32 extern "C" {
  33 #endif
  34
  35 #include <sys/inttypes.h>
  36 #include <sys/zfs_context.h>
  37 #include <sys/refcount.h>
  38
  39 /*
  40  * A reader-writer lock implementation that allows re-entrant reads, but
  41  * still gives writers priority on "new" reads.
  42  *
  43  * See rrwlock.c for more details about the implementation.
  44  *
  45  * Fields of the rrwlock_t structure:
  46  * - rr_lock: protects modification and reading of rrwlock_t fields
  47  * - rr_cv: cv for waking up readers or waiting writers
  48  * - rr_writer: thread id of the current writer
  49  * - rr_anon_rount: number of active anonymous readers
  50  * - rr_linked_rcount: total number of non-anonymous active readers
  51  * - rr_writer_wanted: a writer wants the lock
  52  */
  53 typedef struct rrwlock {
  54         kmutex_t        rr_lock;
  55         kcondvar_t      rr_cv;
  56         kthread_t       *rr_writer;
  57         refcount_t      rr_anon_rcount;
  58         refcount_t      rr_linked_rcount;
  59         boolean_t       rr_writer_wanted;
  60 } rrwlock_t;
  61
  62 /*
  63  * 'tag' is used in reference counting tracking.  The
  64  * 'tag' must be the same in a rrw_enter() as in its
  65  * corresponding rrw_exit().
  66  */
  67 void rrw_init(rrwlock_t *rrl);
  68 void rrw_destroy(rrwlock_t *rrl);
  69 void rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag);
  70 void rrw_exit(rrwlock_t *rrl, void *tag);
  71 boolean_t rrw_held(rrwlock_t *rrl, krw_t rw);
  72
  73 #define RRW_READ_HELD(x)        rrw_held(x, RW_READER)
  74 #define RRW_WRITE_HELD(x)       rrw_held(x, RW_WRITER)
  75
  76 #ifdef  __cplusplus
  77 }
  78 #endif
  79
  80 #endif  /* _SYS_RR_RW_LOCK_H */