fix: use err from Syscall instead of calling GetLastError

Call() already returns the last error, see
https://pkg.go.dev/syscall?GOOS=windows#Proc.Call.

However, some code called GetLastError() afterwards, which is racy;
if the go routine switches threads between Call() and GetLastError(),
it may return a different error than expected, or possibly nil.

cpu/cpu_windows.go

@@ -71,12 +71,14 @@ func TimesWithContext(_ context.Context, percpu bool) ([]TimesStat, error) {
 	var lpIdleTime common.FILETIME
 	var lpKernelTime common.FILETIME
 	var lpUserTime common.FILETIME
-	r, _, _ := common.ProcGetSystemTimes.Call(
+	// GetSystemTimes returns 0 for error, in which case we check err,
+	// see https://pkg.go.dev/golang.org/x/sys/windows#LazyProc.Call
+	r, _, err := common.ProcGetSystemTimes.Call(
 		uintptr(unsafe.Pointer(&lpIdleTime)),
 		uintptr(unsafe.Pointer(&lpKernelTime)),
 		uintptr(unsafe.Pointer(&lpUserTime)))
 	if r == 0 {
-		return ret, windows.GetLastError()
+		return nil, err
 	}
 
 	LOT := float64(0.0000001)

mem/ex_windows.go

@@ -5,8 +5,6 @@ package mem
 
 import (
 	"unsafe"
-
-	"golang.org/x/sys/windows"
 )
 
 // ExVirtualMemory represents Windows specific information
@@ -28,16 +26,21 @@ func NewExWindows() *ExWindows {
 func (e *ExWindows) VirtualMemory() (*ExVirtualMemory, error) {
 	var memInfo memoryStatusEx
 	memInfo.cbSize = uint32(unsafe.Sizeof(memInfo))
-	mem, _, _ := procGlobalMemoryStatusEx.Call(uintptr(unsafe.Pointer(&memInfo)))
+	// If mem == 0 since this is an error according to GlobalMemoryStatusEx documentation
+	// In that case, use err which is constructed from GetLastError(),
+	// see https://pkg.go.dev/golang.org/x/sys/windows#LazyProc.Call
+	mem, _, err := procGlobalMemoryStatusEx.Call(uintptr(unsafe.Pointer(&memInfo)))
 	if mem == 0 {
-		return nil, windows.GetLastError()
+		return nil, err
 	}
 
 	var perfInfo performanceInformation
 	perfInfo.cb = uint32(unsafe.Sizeof(perfInfo))
-	perf, _, _ := procGetPerformanceInfo.Call(uintptr(unsafe.Pointer(&perfInfo)), uintptr(perfInfo.cb))
+	// Analogous to above: perf == 0 is an error according to the GetPerformanceInfo documentation,
+	// use err in that case
+	perf, _, err := procGetPerformanceInfo.Call(uintptr(unsafe.Pointer(&perfInfo)), uintptr(perfInfo.cb))
 	if perf == 0 {
-		return nil, windows.GetLastError()
+		return nil, err
 	}
 
 	ret := &ExVirtualMemory{

mem/mem_windows.go

@@ -40,9 +40,11 @@ func VirtualMemory() (*VirtualMemoryStat, error) {
 func VirtualMemoryWithContext(_ context.Context) (*VirtualMemoryStat, error) {
 	var memInfo memoryStatusEx
 	memInfo.cbSize = uint32(unsafe.Sizeof(memInfo))
-	mem, _, _ := procGlobalMemoryStatusEx.Call(uintptr(unsafe.Pointer(&memInfo)))
+	// GlobalMemoryStatusEx returns 0 for error, in which case we check err,
+	// see https://pkg.go.dev/golang.org/x/sys/windows#LazyProc.Call
+	mem, _, err := procGlobalMemoryStatusEx.Call(uintptr(unsafe.Pointer(&memInfo)))
 	if mem == 0 {
-		return nil, windows.GetLastError()
+		return nil, err
 	}
 
 	ret := &VirtualMemoryStat{
@@ -93,9 +95,11 @@ func SwapMemoryWithContext(_ context.Context) (*SwapMemoryStat, error) {
 	// Get total memory from performance information
 	var perfInfo performanceInformation
 	perfInfo.cb = uint32(unsafe.Sizeof(perfInfo))
-	mem, _, _ := procGetPerformanceInfo.Call(uintptr(unsafe.Pointer(&perfInfo)), uintptr(perfInfo.cb))
+	// GetPerformanceInfo returns 0 for error, in which case we check err,
+	// see https://pkg.go.dev/golang.org/x/sys/windows#LazyProc.Call
+	mem, _, err := procGetPerformanceInfo.Call(uintptr(unsafe.Pointer(&perfInfo)), uintptr(perfInfo.cb))
 	if mem == 0 {
-		return nil, windows.GetLastError()
+		return nil, err
 	}
 	totalPhys := perfInfo.physicalTotal * perfInfo.pageSize
 	totalSys := perfInfo.commitLimit * perfInfo.pageSize
@@ -161,9 +165,11 @@ func SwapDevicesWithContext(_ context.Context) ([]*SwapDevice, error) {
 	// the following system call invokes the supplied callback function once for each page file before returning
 	// see https://docs.microsoft.com/en-us/windows/win32/api/psapi/nf-psapi-enumpagefilesw
 	var swapDevices []*SwapDevice
-	result, _, _ := procEnumPageFilesW.Call(windows.NewCallback(pEnumPageFileCallbackW), uintptr(unsafe.Pointer(&swapDevices)))
+	// EnumPageFilesW returns 0 for error, in which case we check err,
+	// see https://pkg.go.dev/golang.org/x/sys/windows#LazyProc.Call
+	result, _, err := procEnumPageFilesW.Call(windows.NewCallback(pEnumPageFileCallbackW), uintptr(unsafe.Pointer(&swapDevices)))
 	if result == 0 {
-		return nil, windows.GetLastError()
+		return nil, err
 	}
 
 	return swapDevices, nil