[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>

diff --git a/src/core/process.c b/src/core/process.c
index c6660f22759fb9ca638bbcc777d9c17e32e9de11..4a705ef62ce68cf5878dd99ea09c82524551866f 100644 (file)
--- 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 f8b10a8ae95235b5e3b2b35abff999bf8694c03e..9b757981794be21eee4009352de1e79895b266a9 100644 (file)
--- 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 ))