GH-551 use set for threadIds; presize HashMap-s to avoid their resizing

Author: thurka

visualvm/libs.profiler/lib.profiler/src/org/graalvm/visualvm/lib/jfluid/results/cpu/StackTraceSnapshotBuilder.java

@@ -270,7 +270,7 @@ private long getThreadId() {
 
     }
 
-    final List<Long> threadIds = new ArrayList<>();
+    final Set<Long> threadIds = new HashSet<>();
     final List<String> threadNames = new ArrayList<>();
     final List<byte[]> threadCompactData = new ArrayList<>();
     final List<MethodInfo> methodInfos = new ArrayList<>();
@@ -350,7 +350,7 @@ final void addStacktrace(SampledThreadInfo[] threads, long dumpTimeStamp) throws
 
         if (timediff < 0) return;
         synchronized (lock) {
-            Map<Long,SampledThreadInfo> tinfoMap = new HashMap();
+            Map<Long,SampledThreadInfo> tinfoMap = new HashMap(threads.length);
 
             for (SampledThreadInfo tinfo : threads) {
                 tinfoMap.put(tinfo.getThreadId(),tinfo);
@@ -390,7 +390,7 @@ final public void addStacktrace(java.lang.management.ThreadInfo[] threads, long
 
         if (timediff < 0) return;
         synchronized (lock) {
-            Map<Long,SampledThreadInfo> tinfoMap = new HashMap();
+            Map<Long,SampledThreadInfo> tinfoMap = new HashMap(threads.length);
 
             //            if (stackTraceCount%builderBatchSize == 0) {
             //                ccgb.doBatchStart();