LXR qemu/include/qemu/rfifolock.h

   1/*
   2 * Recursive FIFO lock
   3 *
   4 * Copyright Red Hat, Inc. 2013
   5 *
   6 * Authors:
   7 *  Stefan Hajnoczi   <stefanha@redhat.com>
   8 *
   9 * This work is licensed under the terms of the GNU GPL, version 2 or later.
  10 * See the COPYING file in the top-level directory.
  11 *
  12 */
  13
  14#ifndef QEMU_RFIFOLOCK_H
  15#define QEMU_RFIFOLOCK_H
  16
  17#include "qemu/thread.h"
  18
  19/* Recursive FIFO lock
  20 *
  21 * This lock provides more features than a plain mutex:
  22 *
  23 * 1. Fairness - enforces FIFO order.
  24 * 2. Nesting - can be taken recursively.
  25 * 3. Contention callback - optional, called when thread must wait.
  26 *
  27 * The recursive FIFO lock is heavyweight so prefer other synchronization
  28 * primitives if you do not need its features.
  29 */
  30typedef struct {
  31    QemuMutex lock;             /* protects all fields */
  32
  33    /* FIFO order */
  34    unsigned int head;          /* active ticket number */
  35    unsigned int tail;          /* waiting ticket number */
  36    QemuCond cond;              /* used to wait for our ticket number */
  37
  38    /* Nesting */
  39    QemuThread owner_thread;    /* thread that currently has ownership */
  40    unsigned int nesting;       /* amount of nesting levels */
  41
  42    /* Contention callback */
  43    void (*cb)(void *);         /* called when thread must wait, with ->lock
  44                                 * held so it may not recursively lock/unlock
  45                                 */
  46    void *cb_opaque;
  47} RFifoLock;
  48
  49void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque);
  50void rfifolock_destroy(RFifoLock *r);
  51void rfifolock_lock(RFifoLock *r);
  52void rfifolock_unlock(RFifoLock *r);
  53
  54#endif /* QEMU_RFIFOLOCK_H */
  55