Lightweight synchronization mechanism

* Makefrag.am (libkernel_a_SOURCES): Add kern/gsync.c and kern/gsync.h.
* include/mach/gnumach.defs (gsync_wait, gsync_wake, gsync_requeue): New
routines.
* include/mach/kern_return.h (KERN_TIMEDOUT, KERN_INTERRUPTED): New error
codes.
* kern/gsync.c: New file.
* kern/gsync.h: New file.
* kern/startup.c: Include <kern/gsync.h>
(setup_main): Call gsync_setup.

2 files changed, 58 insertions, 0 deletions

diff --git a/include/mach/gnumach.defs b/include/mach/gnumach.defs
index dd4da870..5235df63 100644
--- a/include/mach/gnumach.defs
+++ b/include/mach/gnumach.defs
@@ -84,3 +84,55 @@ simpleroutine task_set_name(
 routine register_new_task_notification(
 		host_priv	: host_priv_t;
 		notification	: mach_port_send_t);
+
+/* Test that the contents of ADDR are equal to the 32-bit integer VAL1.
+ * If they are not, return immediately, otherwise, block until a
+ * matching 'gsync_wake' is done on the same address. FLAGS is used
+ * to control how the thread waits, and may be composed of:
+ * - GSYNC_SHARED: The address may be shared among tasks. If this
+     bit is not set, the address is assumed to be task-local.
+ * - GSYNC_QUAD: Additionally check that the adjacent 32-bit word
+     following ADDR matches the value VAL2.
+ * - GSYNC_TIMED: The call only blocks for MSEC milliseconds. */
+routine gsync_wait(
+  task : task_t;
+  addr : vm_offset_t;
+  val1 : unsigned;
+  val2 : unsigned;
+  msec : natural_t;
+  flags : int);
+
+/* Wake up threads waiting on the address ADDR. Much like with
+ * 'gsync_wait', the parameter FLAGS controls how it is done. In this
+ * case, it may be composed of the following:
+ * - GSYNC_SHARED: Same as with 'gsync_wait'.
+ * - GSYNC_BROADCAST: Wake up every thread waiting on the address. If
+ *   this flag is not set, the call wakes (at most) 1 thread.
+ * - GSYNC_MUTATE: Before waking any potential waiting threads, set the
+ *   contents of ADDR to VAL.
+ *
+ * This RPC is implemented as a simple routine for efficiency reasons,
+ * and because the return value rarely matters. */
+simpleroutine gsync_wake(
+  task : task_t;
+  addr : vm_offset_t;
+  val : unsigned;
+  flags : int);
+
+/* Arrange for threads waiting on address SRC_ADDR to instead
+ * wait on address DST_ADDR. If WAKE_ONE is true, additionally
+ * wake one of the threads waiting on SRC_ADDR. For this function,
+ * the parameter flags may be a combination of:
+ * - GSYNC_SHARED: Just like with 'gsync_wait' and 'gsync_wake'.
+ * - GSYNC_BROADCAST: Move all the threads waiting on SRC_ADDR. If
+     this flag is not set, the call moves (at most) 1 thread.
+ *
+ * This RPC is also a simple routine, and for the same reasons as
+ * with 'gsync_wake'. */
+simpleroutine gsync_requeue(
+  task : task_t;
+  src_addr : vm_offset_t;
+  dst_addr : vm_offset_t;
+  wake_one : boolean_t;
+  flags : int);
+
diff --git a/include/mach/kern_return.h b/include/mach/kern_return.h
index 2274328b..a9d16e94 100644
--- a/include/mach/kern_return.h
+++ b/include/mach/kern_return.h
@@ -157,4 +157,10 @@
 		/* Object has been terminated and is no longer available.
 		 */
 
+#define KERN_TIMEDOUT           27
+        /* Kernel operation timed out. */
+
+#define KERN_INTERRUPTED        28
+        /* Kernel operation was interrupted. */
+
 #endif	/* _MACH_KERN_RETURN_H_ */