Persist network stats using AtomicFile.
Implements read/write of network stats using AtomicFile, along with
magic number and versioning. Stores in "/data/system/netstats.bin"
for now. Tests to verify that stats are persisted across a simulated
reboot, and to verify that TEMPLATE_WIFI is working.
Fixed bug where kernel counters rolling backwards would cause negative
stats to be recorded; now we clamp deltas at 0.
Change-Id: I53bce26fc8fd3f4ab1e34ce135d302edfa34db34
diff --git a/core/java/android/net/NetworkStats.java b/core/java/android/net/NetworkStats.java
index ee415fa..6354e9a 100644
--- a/core/java/android/net/NetworkStats.java
+++ b/core/java/android/net/NetworkStats.java
@@ -158,10 +158,37 @@
* between two snapshots in time. Assumes that statistics rows collect over
* time, and that none of them have disappeared.
*
+ * @throws IllegalArgumentException when given {@link NetworkStats} is
+ * non-monotonic.
+ */
+ public NetworkStats subtract(NetworkStats value) {
+ return subtract(value, true, false);
+ }
+
+ /**
+ * Subtract the given {@link NetworkStats}, effectively leaving the delta
+ * between two snapshots in time. Assumes that statistics rows collect over
+ * time, and that none of them have disappeared.
+ * <p>
+ * Instead of throwing when counters are non-monotonic, this variant clamps
+ * results to never be negative.
+ */
+ public NetworkStats subtractClamped(NetworkStats value) {
+ return subtract(value, false, true);
+ }
+
+ /**
+ * Subtract the given {@link NetworkStats}, effectively leaving the delta
+ * between two snapshots in time. Assumes that statistics rows collect over
+ * time, and that none of them have disappeared.
+ *
* @param enforceMonotonic Validate that incoming value is strictly
* monotonic compared to this object.
+ * @param clampNegative Instead of throwing like {@code enforceMonotonic},
+ * clamp resulting counters at 0 to prevent negative values.
*/
- public NetworkStats subtract(NetworkStats value, boolean enforceMonotonic) {
+ private NetworkStats subtract(
+ NetworkStats value, boolean enforceMonotonic, boolean clampNegative) {
final long deltaRealtime = this.elapsedRealtime - value.elapsedRealtime;
if (enforceMonotonic && deltaRealtime < 0) {
throw new IllegalArgumentException("found non-monotonic realtime");
@@ -181,11 +208,15 @@
result.addEntry(iface, uid, this.rx[i], this.tx[i]);
} else {
// existing row, subtract remote value
- final long rx = this.rx[i] - value.rx[j];
- final long tx = this.tx[i] - value.tx[j];
+ long rx = this.rx[i] - value.rx[j];
+ long tx = this.tx[i] - value.tx[j];
if (enforceMonotonic && (rx < 0 || tx < 0)) {
throw new IllegalArgumentException("found non-monotonic values");
}
+ if (clampNegative) {
+ rx = Math.max(0, rx);
+ tx = Math.max(0, tx);
+ }
result.addEntry(iface, uid, rx, tx);
}
}