Re: [Qemu-devel] [PATCH 1/2] rfifolock: add recursive FIFO lock

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

于 2013/10/11 21:35, Stefan Hajnoczi 写道:
> On Fri, Oct 11, 2013 at 04:55:31PM +0800, Wenchao Xia wrote:
>>> +/* Recursive FIFO lock
>>> + *
>>> + * This lock provides more features than a plain mutex:
>>> + *
>>> + * 1. Fairness - enforces FIFO order.
>>> + * 2. Nesting - can be taken recursively.
>>> + * 3. Contention callback - optional, called when thread must wait.
>>> + *
>>> + * The recursive FIFO lock is heavyweight so prefer other synchronization
>>> + * primitives if you do not need its features.
>>> + */
>>> +typedef struct {
>>> +    QemuMutex lock;             /* protects all fields */
>>> +
>>> +    /* FIFO order */
>>> +    unsigned int head;          /* active ticket number */
>>> +    unsigned int tail;          /* waiting ticket number */
>>> +    QemuCond cond;              /* used to wait for our ticket number */
>>> +
>>> +    /* Nesting */
>>> +    QemuThread owner_thread;    /* thread that currently has ownership */
>>> +    unsigned int nesting;       /* amount of nesting levels */
>>> +
>>> +    /* Contention callback */
>>> +    void (*cb)(void *);         /* called when thread must wait, with ->lock
>>> +                                 * held so it may not recursively lock/unlock
>>> +                                 */
>>> +    void *cb_opaque;
>>> +} RFifoLock;
>>> +
>> If you respin, the define can be moved to util/rfifolock.c, leave
>> typedef struct RFifoLock RFifoLock;
>> in header.
> Then the struct cannot be embedded as a field, it would require heap
> allocation of all RFifoLocks.
>
> This is why I chose to include the definition in the header file.
>
> Stefan
>
OK, it is not serious problem, the patch looks good to me.