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  */
  30 typedef 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
  49 void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque);
  50 void rfifolock_destroy(RFifoLock *r);
  51 void rfifolock_lock(RFifoLock *r);
  52 void rfifolock_unlock(RFifoLock *r);
  53
  54 #endif /* QEMU_RFIFOLOCK_H */