Added a real yield function to the kernel (using the next_priority approach).

The test application lets run a thread at the highest priority that calls
yield all the time - the system stays responsible when it runs, so it seems
to work fine :)
Changed the malloc implementation to use _kern_thread_yield() instead of
snoozing.
We should think about making this call public, too.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@16166 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/syscalls.h

@@ -96,6 +96,7 @@ extern status_t		_kern_rename_thread(thread_id thread, const char *newName);
 extern status_t		_kern_set_thread_priority(thread_id thread, int32 newPriority);
 extern status_t		_kern_kill_thread(thread_id thread);
 extern void			_kern_exit_thread(status_t returnValue);
+extern void			_kern_thread_yield(void);
 extern status_t		_kern_wait_for_thread(thread_id thread, status_t *_returnCode);
 extern bool			_kern_has_data(thread_id thread);
 extern status_t		_kern_send_data(thread_id thread, int32 code, const void *buffer, size_t bufferSize);

headers/private/kernel/thread.h

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2005, Axel Dörfler, [email protected].
+ * Copyright 2002-2006, Axel Dörfler, [email protected].
  * Distributed under the terms of the MIT License.
  *
  * Copyright 2001-2002, Travis Geiselbrecht. All rights reserved.
@@ -31,6 +31,7 @@ void thread_at_kernel_exit(void);
 
 status_t thread_init(struct kernel_args *args);
 status_t thread_per_cpu_init(int32 cpuNum);
+void thread_yield(void);
 void thread_exit(void);
 
 bigtime_t thread_get_active_cpu_time(int32 cpuNum);
@@ -66,6 +67,7 @@ thread_id _user_spawn_thread(thread_entry_func entry, const char *name, int32 pr
 status_t _user_wait_for_thread(thread_id id, status_t *_returnCode);
 status_t _user_snooze_etc(bigtime_t timeout, int timebase, uint32 flags);
 status_t _user_kill_thread(thread_id thread);
+void _user_thread_yield(void);
 void _user_exit_thread(status_t return_value);
 bool _user_has_data(thread_id thread);
 status_t _user_send_data(thread_id thread, int32 code, const void *buffer, size_t buffer_size);

src/system/kernel/thread.c

@@ -1232,19 +1232,40 @@ thread_dequeue_id(struct thread_queue *q, thread_id id)
 
 
 thread_id
-allocate_thread_id()
+allocate_thread_id(void)
 {
 	return atomic_add(&sNextThreadID, 1);
 }
 
 
 thread_id
-peek_next_thread_id()
+peek_next_thread_id(void)
 {
 	return atomic_get(&sNextThreadID);
 }
 
 
+void
+thread_yield(void)
+{
+	cpu_status state;
+
+	struct thread *thread = thread_get_current_thread();
+	if (thread == NULL)
+		return;
+
+	state = disable_interrupts();
+	GRAB_THREAD_LOCK();
+
+	// just add the thread at the end of the run queue
+	thread->next_priority = B_LOWEST_ACTIVE_PRIORITY;
+	scheduler_reschedule();
+
+	RELEASE_THREAD_LOCK();
+	restore_interrupts(state);
+}
+
+
 /** Kernel private thread creation function.
  *
  * \param threadID The ID to be assigned to the new thread. If
@@ -2044,6 +2065,13 @@ _user_snooze_etc(bigtime_t timeout, int timebase, uint32 flags)
 }
 
 
+void
+_user_thread_yield(void)
+{
+	thread_yield();
+}
+
+
 status_t
 _user_get_thread_info(thread_id id, thread_info *userInfo)
 {

src/system/libroot/posix/malloc/arch-specific.cpp

@@ -317,10 +317,7 @@ hoardUnlock(hoardLockType &lock)
 void
 hoardYield(void)
 {
-	// We need to snooze longer than a thread quantum (3ms) to ensure
+	_kern_thread_yield();
-	// real-time threads won't hog the CPU completely
-	// ToDo: we should have a real one in the kernel
-	snooze(4000);
 }
 
 }	// namespace BPrivate

src/tests/system/kernel/Jamfile

@@ -1,20 +1,19 @@
 SubDir HAIKU_TOP src tests system kernel ;
 
 UsePrivateHeaders kernel ;
-
+UseHeaders $(TARGET_PRIVATE_KERNEL_HEADERS) : true ;
-if $(TARGET_PLATFORM) = r5 {
-	LIBROOT = root ;
-} else {
-	LIBROOT = libroot.so ;
-}
 
 SimpleTest transfer_area_test :
 	transfer_area_test.cpp
-	: libroot.so ;
+	;
 
 SimpleTest syscall_time :
 	syscall_time.cpp
-	: $(LIBROOT) ;
+	;
+
+SimpleTest yield_test :
+	yield_test.cpp
+	;
 
 SubInclude HAIKU_TOP src tests system kernel cache ;
 #SubInclude HAIKU_TOP src tests system kernel disk_device_manager ;

src/tests/system/kernel/yield_test.cpp

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2006, Axel Dörfler, axeld@pinc-software.de.
+ * Distributed under the terms of the MIT License.
+ */
+
+
+#include <OS.h>
+#include <syscalls.h>
+
+
+status_t
+looper(void *)
+{
+	while (true) {
+		_kern_thread_yield();
+	}
+
+	return B_OK;
+}
+
+
+int
+main()
+{
+	thread_id thread = spawn_thread(looper, "Real-Time Looper", B_REAL_TIME_PRIORITY, NULL);
+	if (thread < B_OK)
+		return -1;
+
+	resume_thread(thread);
+	wait_for_thread(thread, NULL);
+
+	return 0;
+}