From ccc2655540f01cc4da018fc31fa16ce8cdb1f4b5 Mon Sep 17 00:00:00 2001
From: Michael Brown <mcb30@ipxe.org>
Date: Fri, 24 Jun 2011 14:18:48 +0100
Subject: [PATCH] [process] Add support for one-shot processes

Some processes execute only once, and exist solely in order to defer
execution until after the relevant instantiator method has returned.
Such processes do not need to be automatically rescheduled when
executing.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/core/process.c         |  8 ++++++--
 src/include/ipxe/process.h | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/core/process.c b/src/core/process.c
index c6660f22..4a705ef6 100644
--- a/src/core/process.c
+++ b/src/core/process.c
@@ -100,8 +100,12 @@ void step ( void ) {
 		ref_get ( process->refcnt ); /* Inhibit destruction mid-step */
 		desc = process->desc;
 		object = process_object ( process );
-		list_del ( &process->list );
-		list_add_tail ( &process->list, &run_queue );
+		if ( desc->reschedule ) {
+			list_del ( &process->list );
+			list_add_tail ( &process->list, &run_queue );
+		} else {
+			process_del ( process );
+		}
 		DBGC2 ( PROC_COL ( process ), "PROCESS " PROC_FMT
 			" executing\n", PROC_DBG ( process ) );
 		desc->step ( object );
diff --git a/src/include/ipxe/process.h b/src/include/ipxe/process.h
index f8b10a8a..9b757981 100644
--- a/src/include/ipxe/process.h
+++ b/src/include/ipxe/process.h
@@ -39,6 +39,8 @@ struct process_descriptor {
 	 * CPU to another process.
 	 */
 	void ( * step ) ( void *object );
+	/** Automatically reschedule the process */
+	int reschedule;
 };
 
 /**
@@ -78,6 +80,21 @@ struct process_descriptor {
 #define PROC_DESC( object_type, process, _step ) {			      \
 		.offset = process_offset ( object_type, process ),	      \
 		.step = PROC_STEP ( object_type, _step ),		      \
+		.reschedule = 1,					      \
+	}
+
+/**
+ * Define a process descriptor for a process that runs only once
+ *
+ * @v object_type	Containing object data type
+ * @v process		Process name (i.e. field within object data type)
+ * @v step		Process' step() method
+ * @ret desc		Object interface descriptor
+ */
+#define PROC_DESC_ONCE( object_type, process, _step ) {			      \
+		.offset = process_offset ( object_type, process ),	      \
+		.step = PROC_STEP ( object_type, _step ),		      \
+		.reschedule = 0,					      \
 	}
 
 /**
@@ -91,6 +108,7 @@ struct process_descriptor {
 #define PROC_DESC_PURE( _step ) {					      \
 		.offset = 0,						      \
 		.step = PROC_STEP ( struct process, _step ),		      \
+		.reschedule = 1,					      \
 	}
 
 extern void * __attribute__ (( pure ))