windows: add functions for priority class

took const value from
https://docs.microsoft.com/en-us/windows/desktop/api/processthreadsapi/nf-processthreadsapi-setpriorityclass
https://docs.microsoft.com/en-us/windows/desktop/api/processthreadsapi/nf-processthreadsapi-getpriorityclass

Change-Id: I376bb8e1f5de8968177512857d60169cb7b7c776
Reviewed-on: https://go-review.googlesource.com/c/sys/+/179038
Reviewed-by: Alex Brainman <[email protected]>
Run-TryBot: Alex Brainman <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: atetubou

windows/syscall_windows.go

@@ -258,6 +258,8 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	TerminateJobObject(job Handle, exitCode uint32) (err error) = kernel32.TerminateJobObject
 //sys	SetErrorMode(mode uint32) (ret uint32) = kernel32.SetErrorMode
 //sys	ResumeThread(thread Handle) (ret uint32, err error) [failretval==0xffffffff] = kernel32.ResumeThread
+//sys	SetPriorityClass(process Handle, priorityClass uint32) (err error) = kernel32.SetPriorityClass
+//sys	GetPriorityClass(process Handle) (ret uint32, err error) = kernel32.GetPriorityClass
 
 // Volume Management Functions
 //sys	DefineDosDevice(flags uint32, deviceName *uint16, targetPath *uint16) (err error) = DefineDosDeviceW

windows/types_windows.go

@@ -408,6 +408,18 @@ const (
 	SEM_NOOPENFILEERRORBOX     = 0x8000
 )
 
+const (
+	// Priority class.
+	ABOVE_NORMAL_PRIORITY_CLASS   = 0x00008000
+	BELOW_NORMAL_PRIORITY_CLASS   = 0x00004000
+	HIGH_PRIORITY_CLASS           = 0x00000080
+	IDLE_PRIORITY_CLASS           = 0x00000040
+	NORMAL_PRIORITY_CLASS         = 0x00000020
+	PROCESS_MODE_BACKGROUND_BEGIN = 0x00100000
+	PROCESS_MODE_BACKGROUND_END   = 0x00200000
+	REALTIME_PRIORITY_CLASS       = 0x00000100
+)
+
 var (
 	OID_PKIX_KP_SERVER_AUTH = []byte("1.3.6.1.5.5.7.3.1\x00")
 	OID_SERVER_GATED_CRYPTO = []byte("1.3.6.1.4.1.311.10.3.3\x00")