kernel: add new work queue implementation

This commit provides a complete reimplementation of the work queue
infrastructure intended to eliminate the race conditions and feature
gaps in the existing implementation.

Both bare and delayable work structures are supported.  Items can be
submitted; delayable items can be scheduled for submission at a future
time.  Items can be delayed, queued, and running all at the same time.
A running item can also be canceling.

The new implementation:
* replaces "pending" with "busy" which identifies the active states;
* supports canceling delayed and submitted items;
* prevents resubmission of a item being canceled until cancellation
  completes;
* supports waiting for cancellation to complete;
* supports flushing a work item (waiting for the last submission to
  complete without preventing resubmission);
* supports waiting for a queue to drain (only allows resubmission from
  the work thread);
* supports stopping a work queue in conjunction with draining it;
* prevents handler-reentrancy during resubmission.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>

kernel/CMakeLists.txt

@@ -45,6 +45,7 @@ set_target_properties(
   )
 
 target_sources_ifdef(CONFIG_KERNEL_WORK1          kernel PRIVATE work_q.c)
+target_sources_ifdef(CONFIG_KERNEL_WORK2          kernel PRIVATE work.c)
 
 target_sources_ifdef(CONFIG_STACK_CANARIES        kernel PRIVATE compiler_stack_protect.c)
 target_sources_ifdef(CONFIG_SYS_CLOCK_EXISTS      kernel PRIVATE timeout.c timer.c)

kernel/Kconfig

@@ -396,6 +396,15 @@ config SYSTEM_WORKQUEUE_PRIORITY
 	  priority. This means that any work handler, once started, won't
 	  be preempted by any other thread until finished.
 
+config SYSTEM_WORKQUEUE_NO_YIELD
+	bool "Select whether system work queue yields"
+	help
+	  By default, the system work queue yields between each work item, to
+	  prevent other threads from being starved.  Selecting this removes
+	  this yield, which may be useful if the work queue thread is
+	  cooperative and a sequence of work items is expected to complete
+	  without yielding.
+
 endmenu
 
 menu "Atomic Operations"

kernel/system_work_q.c

@@ -14,19 +14,31 @@
 #include <kernel.h>
 #include <init.h>
 
-K_KERNEL_STACK_DEFINE(sys_work_q_stack, CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE);
+static K_KERNEL_STACK_DEFINE(sys_work_q_stack,
+			     CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE);
 
 struct k_work_q k_sys_work_q;
 
 static int k_sys_work_q_init(const struct device *dev)
 {
 	ARG_UNUSED(dev);
+	struct k_work_queue_config cfg = {
+		.name = "sysworkq",
+		.no_yield = IS_ENABLED(CONFIG_SYSTEM_WORKQUEUE_NO_YIELD),
+	};
 
+#ifdef CONFIG_KERNEL_WORK1
 	k_work_q_start(&k_sys_work_q,
 		       sys_work_q_stack,
 		       K_KERNEL_STACK_SIZEOF(sys_work_q_stack),
 		       CONFIG_SYSTEM_WORKQUEUE_PRIORITY);
 	k_thread_name_set(&k_sys_work_q.thread, "sysworkq");
+#else /* CONFIG_KERNEL_WORK1 */
+	k_work_queue_start(&k_sys_work_q,
+			    sys_work_q_stack,
+			    K_KERNEL_STACK_SIZEOF(sys_work_q_stack),
+			    CONFIG_SYSTEM_WORKQUEUE_PRIORITY, &cfg);
+#endif /* CONFIG_KERNEL_WORK1 */
 
 	return 0;
 }