Better LocalLog

This patch fixes the following issues in LocalLog:
  - reverseDump() uses a descending iterator with linear complexity
    instead of a quadratic loop using get(index) on a linked list.
  - reverseDump() is added to ReadOnlyLocalLog.
  - synchronized section in log() is restricted to mutation of internal
    list.
  - formatting of the log message does not create an internal
    StringBuilder.
  - the instance variable mNow is removed: it was only used inside log()
    as a local variable.
  - remaining instance variables are qualified with final.
  - the linked list is replaced by a fixed capacity array-backed queue.

Test: added unit tests
Change-Id: I1a54f0ad26dd35448d3297ea24df1fd626d20ef3

1 files changed, 26 insertions, 18 deletions

diff --git a/core/java/android/util/LocalLog.java b/core/java/android/util/LocalLog.java
index 39f66a5f18fc..665c583a56ab 100644
--- a/core/java/android/util/LocalLog.java
+++ b/core/java/android/util/LocalLog.java
@@ -20,44 +20,49 @@ import java.io.FileDescriptor;
 import java.io.PrintWriter;
 import java.util.Calendar;
 import java.util.Iterator;
-import java.util.LinkedList;
+import java.util.Deque;
+import java.util.ArrayDeque;
 
 /**
  * @hide
  */
 public final class LocalLog {
 
-    private LinkedList<String> mLog;
-    private int mMaxLines;
-    private long mNow;
+    private final Deque<String> mLog;
+    private final int mMaxLines;
 
     public LocalLog(int maxLines) {
-        mLog = new LinkedList<String>();
-        mMaxLines = maxLines;
+        mMaxLines = Math.max(0, maxLines);
+        mLog = new ArrayDeque<>(mMaxLines);
     }
 
-    public synchronized void log(String msg) {
-        if (mMaxLines > 0) {
-            mNow = System.currentTimeMillis();
-            StringBuilder sb = new StringBuilder();
-            Calendar c = Calendar.getInstance();
-            c.setTimeInMillis(mNow);
-            sb.append(String.format("%tm-%td %tH:%tM:%tS.%tL", c, c, c, c, c, c));
-            mLog.add(sb.toString() + " - " + msg);
-            while (mLog.size() > mMaxLines) mLog.remove();
+    public void log(String msg) {
+        if (mMaxLines <= 0) {
+            return;
         }
+        Calendar c = Calendar.getInstance();
+        c.setTimeInMillis(System.currentTimeMillis());
+        append(String.format("%tm-%td %tH:%tM:%tS.%tL - %s", c, c, c, c, c, c, msg));
+    }
+
+    private synchronized void append(String logLine) {
+        while (mLog.size() >= mMaxLines) {
+            mLog.remove();
+        }
+        mLog.add(logLine);
     }
 
     public synchronized void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
-        Iterator<String> itr = mLog.listIterator(0);
+        Iterator<String> itr = mLog.iterator();
         while (itr.hasNext()) {
             pw.println(itr.next());
         }
     }
 
     public synchronized void reverseDump(FileDescriptor fd, PrintWriter pw, String[] args) {
-        for (int i = mLog.size() - 1; i >= 0; i--) {
-            pw.println(mLog.get(i));
+        Iterator<String> itr = mLog.descendingIterator();
+        while (itr.hasNext()) {
+            pw.println(itr.next());
         }
     }
 
@@ -69,6 +74,9 @@ public final class LocalLog {
         public void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
             mLog.dump(fd, pw, args);
         }
+        public void reverseDump(FileDescriptor fd, PrintWriter pw, String[] args) {
+            mLog.reverseDump(fd, pw, args);
+        }
     }
 
     public ReadOnlyLocalLog readOnlyLocalLog() {