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 <alex.brainman@gmail.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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")

windows/zsyscall_windows.go

@@ -196,6 +196,8 @@ var (
 	procTerminateJobObject                 = modkernel32.NewProc("TerminateJobObject")
 	procSetErrorMode                       = modkernel32.NewProc("SetErrorMode")
 	procResumeThread                       = modkernel32.NewProc("ResumeThread")
+	procSetPriorityClass                   = modkernel32.NewProc("SetPriorityClass")
+	procGetPriorityClass                   = modkernel32.NewProc("GetPriorityClass")
 	procDefineDosDeviceW                   = modkernel32.NewProc("DefineDosDeviceW")
 	procDeleteVolumeMountPointW            = modkernel32.NewProc("DeleteVolumeMountPointW")
 	procFindFirstVolumeW                   = modkernel32.NewProc("FindFirstVolumeW")
@@ -2105,6 +2107,31 @@ func ResumeThread(thread Handle) (ret uint32, err error) {
 	return
 }
 
+func SetPriorityClass(process Handle, priorityClass uint32) (err error) {
+	r1, _, e1 := syscall.Syscall(procSetPriorityClass.Addr(), 2, uintptr(process), uintptr(priorityClass), 0)
+	if r1 == 0 {
+		if e1 != 0 {
+			err = errnoErr(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return
+}
+
+func GetPriorityClass(process Handle) (ret uint32, err error) {
+	r0, _, e1 := syscall.Syscall(procGetPriorityClass.Addr(), 1, uintptr(process), 0, 0)
+	ret = uint32(r0)
+	if ret == 0 {
+		if e1 != 0 {
+			err = errnoErr(e1)
+		} else {
+			err = syscall.EINVAL
+		}
+	}
+	return
+}
+
 func DefineDosDevice(flags uint32, deviceName *uint16, targetPath *uint16) (err error) {
 	r1, _, e1 := syscall.Syscall(procDefineDosDeviceW.Addr(), 3, uintptr(flags), uintptr(unsafe.Pointer(deviceName)), uintptr(unsafe.Pointer(targetPath)))
 	if r1 == 0 {