cmd/syncthing, lib/config, lib/osutil: Lower process priority (fixes #4628)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4675

lib/config/config_test.go

@@ -76,6 +76,7 @@ func TestDefaultValues(t *testing.T) {
 		KCPUpdateIntervalMs:     25,
 		KCPFastResend:           false,
 		DefaultFolderPath:       "~",
+		SetLowPriority:          true,
 	}
 
 	cfg := New(device1)
@@ -224,6 +225,7 @@ func TestOverriddenValues(t *testing.T) {
 		KCPUpdateIntervalMs:     1000,
 		KCPFastResend:           true,
 		DefaultFolderPath:       "/media/syncthing",
+		SetLowPriority:          false,
 	}
 
 	os.Unsetenv("STNOUPGRADE")

lib/config/optionsconfiguration.go

@@ -143,6 +143,7 @@ type OptionsConfiguration struct {
 	KCPSendWindowSize       int                     `xml:"kcpSendWindowSize" json:"kcpSendWindowSize" default:"128"`
 	KCPReceiveWindowSize    int                     `xml:"kcpReceiveWindowSize" json:"kcpReceiveWindowSize" default:"128"`
 	DefaultFolderPath       string                  `xml:"defaultFolderPath" json:"defaultFolderPath" default:"~"`
+	SetLowPriority          bool                    `xml:"setLowPriority" json:"setLowPriority" default:"true"`
 
 	DeprecatedUPnPEnabled        bool     `xml:"upnpEnabled,omitempty" json:"-"`
 	DeprecatedUPnPLeaseM         int      `xml:"upnpLeaseMinutes,omitempty" json:"-"`

lib/config/testdata/overridenvalues.xml

@@ -44,5 +44,6 @@
         <kcpUpdateIntervalMs>1000</kcpUpdateIntervalMs>
         <kcpFastResend>true</kcpFastResend>
         <defaultFolderPath>/media/syncthing</defaultFolderPath>
+        <setLowPriority>false</setLowPriority>
     </options>
 </configuration>