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

[Wenchao Xia]

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.