Let Java copy arrays which it can sometimes do faster than manual loo…

…ps. (openzipkin#2591)
abesto · Sep 10, 2019 · 672e7c4 · 672e7c4
1 parent eb2d725
commit 672e7c4
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Showing 2 changed files with 33 additions and 3 deletions.
diff --git a/benchmarks/src/main/java/zipkin2/SpanBenchmarks.java b/benchmarks/src/main/java/zipkin2/SpanBenchmarks.java
@@ -143,6 +143,26 @@ public byte[] deserialize_kryo() {
     return output.getBuffer();
   }
 
+  @Benchmark
+  public String padLeft_1Char() {
+    return Span.padLeft("1", 16);
+  }
+
+  @Benchmark
+  public String padLeft_15Chars() {
+    return Span.padLeft("123456789012345", 16);
+  }
+
+  @Benchmark
+  public String padLeft_17Chars() {
+    return Span.padLeft("12345678901234567", 32);
+  }
+
+  @Benchmark
+  public String padLeft_31Chars() {
+    return Span.padLeft("1234567890123456789012345678901", 32);
+  }
+
   // Convenience main entry-point
   public static void main(String[] args) throws RunnerException {
     Options opt = new OptionsBuilder()

diff --git a/zipkin/src/main/java/zipkin2/Span.java b/zipkin/src/main/java/zipkin2/Span.java
@@ -659,11 +659,21 @@ public static String normalizeTraceId(String traceId) {
     }
   }
 
+  static final String THIRTY_TWO_ZEROS;
+  static {
+    char[] zeros = new char[32];
+    Arrays.fill(zeros, '0');
+    THIRTY_TWO_ZEROS = new String(zeros);
+  }
+
   static String padLeft(String id, int desiredLength) {
+    int length = id.length();
+    int numZeros = desiredLength - length;
+
     char[] data = Platform.shortStringBuffer();
-    int i = 0, length = id.length(), offset = desiredLength - length;
-    for (; i < offset; i++) data[i] = '0';
-    for (int j = 0; j < length; j++) data[i++] = id.charAt(j);
+    THIRTY_TWO_ZEROS.getChars(0, numZeros, data, 0);
+    id.getChars(0, length, data, numZeros);
+
     return new String(data, 0, desiredLength);
   }