improve speed, thanks to the following improvements: (#550)

* improve speed, thanks to the following improvements:
- loop unrolling and eleminating extra calculations
- eleminating instance level variable access
- quicker equals check, checking long by long chunks instead of bytes
- update GraalVM version to the latest

* faster equals check

* fix equals bug in 10K, more optimizations on equals and calculate hash parts

* New solution optimized for Linux/AMD hardware

* Optimize solution, try to fix 10K bug on native

* Optimize solution, move records to a local field

* test timing

* revert back accidentally pushed code

---------

Co-authored-by: Yavuz Tas <yavuz.tas@ing.com>

1 files changed, 319 insertions, 188 deletions

diff --git a/src/main/java/dev/morling/onebrc/CalculateAverage_yavuztas.java b/src/main/java/dev/morling/onebrc/CalculateAverage_yavuztas.java
index e33fe7e..0e589a4 100644
--- a/src/main/java/dev/morling/onebrc/CalculateAverage_yavuztas.java
+++ b/src/main/java/dev/morling/onebrc/CalculateAverage_yavuztas.java
@@ -17,15 +17,16 @@ package dev.morling.onebrc;
 
 import sun.misc.Unsafe;
 
-import java.io.IOException;
 import java.lang.foreign.Arena;
 import java.lang.reflect.Field;
-import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardOpenOption;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
 import java.util.TreeMap;
 import java.util.function.Consumer;
 
@@ -35,8 +36,9 @@ public class CalculateAverage_yavuztas {
 
     private static final Unsafe UNSAFE = unsafe();
 
-    // Tried all there: MappedByteBuffer, MemorySegment and Unsafe
-    // Accessing the memory using Unsafe is still the fastest in my experience
+    // I compared all three: MappedByteBuffer, MemorySegment and Unsafe.
+    // Accessing the memory using Unsafe is still the fastest in my experience.
+    // However, I would never use it in production, single programming error will crash your app.
     private static Unsafe unsafe() {
         try {
             final Field f = Unsafe.class.getDeclaredField("theUnsafe");
@@ -48,296 +50,419 @@ public class CalculateAverage_yavuztas {
         }
     }
 
-    // Only one object, both for measurements and keys, less object creation in hotpots is always faster
-    static class Record {
-
-        // keep memory starting address for each segment
-        // since we use Unsafe, this is enough to align and fetch the data
-        long segment;
-        int start;
-        int length;
-        int hash;
+    /**
+     * Extract bytes from a long
+     */
+    private static long partial(long word, int length) {
+        final long mask = (~0L) << (length << 3);
+        return word & (~mask);
+    }
 
-        private int min = 1000; // calculations over int is faster than double, we convert to double in the end only once
-        private int max = -1000;
+    // Only one object, both for measurements and keys, less object creation in hotpots is always faster
+    private static final class Record {
+
+        private final long start; // memory address of the underlying data
+        private final int length;
+        private final long word1;
+        private final long word2;
+        private final long wordLast;
+        private final int hash;
+        private Record next; // linked list to resolve hash collisions
+
+        private int min; // calculations over int is faster than double, we convert to double in the end only once
+        private int max;
         private long sum;
-        private long count;
+        private int count;
 
-        public Record(long segment, int start, int length, int hash) {
-            this.segment = segment;
+        public Record(long start, int length, long word1, long word2, long wordLast, int hash, int temp) {
             this.start = start;
             this.length = length;
+            this.word1 = word1;
+            this.word2 = word2;
+            this.wordLast = wordLast;
             this.hash = hash;
+            this.min = temp;
+            this.max = temp;
+            this.sum = temp;
+            this.count = 1;
         }
 
         @Override
         public boolean equals(Object o) {
             final Record record = (Record) o;
-            return equals(record.segment, record.start, record.length, record.hash);
+            return equals(record.start, record.word1, record.word2, record.wordLast, record.length);
         }
 
-        /**
-         * Stateless equals, no Record object needed
-         */
-        public boolean equals(long segment, int start, int length, int hash) {
-            if (this.length != length || this.hash != hash)
-                return false;
+        private static boolean notEquals(long address1, long address2, int step) {
+            return UNSAFE.getLong(address1 + step) != UNSAFE.getLong(address2 + step);
+        }
 
-            int i = 0; // bytes mismatch check
-            while (i < this.length
-                    && UNSAFE.getByte(this.segment + this.start + i) == UNSAFE.getByte(segment + start + i)) {
-                i++;
+        private static boolean equalsComparingLongs(long start1, long start2, int length) {
+            // first shortcuts
+            if (length < 24)
+                return true;
+            if (length < 32)
+                return !notEquals(start1, start2, 16);
+
+            int step = 24; // starting from 3rd long
+            length -= step;
+            while (length >= 8) { // scan longs
+                if (notEquals(start1, start2, step)) {
+                    return false;
+                }
+                length -= 8;
+                step += 8; // 8 bytes
             }
-            return i == this.length;
+            return true;
         }
 
-        @Override
-        public int hashCode() {
-            return this.hash;
+        private boolean equals(long start, long word1, long word2, long last, int length) {
+            if (this.word1 != word1)
+                return false;
+            if (this.word2 != word2)
+                return false;
+
+            // equals check is done by comparing longs instead of byte by byte check, this is faster
+            return equalsComparingLongs(this.start, start, length) && this.wordLast == last;
         }
 
         @Override
         public String toString() {
             final byte[] bytes = new byte[this.length];
-            int i = 0;
-            while (i < this.length) {
-                bytes[i] = UNSAFE.getByte(this.segment + this.start + i++);
-            }
-
+            UNSAFE.copyMemory(null, this.start, bytes, Unsafe.ARRAY_BYTE_BASE_OFFSET, this.length);
             return new String(bytes, StandardCharsets.UTF_8);
         }
 
-        public Record collect(int temp) {
-            this.min = Math.min(this.min, temp);
-            this.max = Math.max(this.max, temp);
+        private void collect(int temp) {
+            if (temp < this.min)
+                this.min = temp;
+            if (temp > this.max)
+                this.max = temp;
             this.sum += temp;
             this.count++;
-            return this;
         }
 
-        public void merge(Record other) {
-            this.min = Math.min(this.min, other.min);
-            this.max = Math.max(this.max, other.max);
-            this.sum += other.sum;
-            this.count += other.count;
+        private void merge(Record that) {
+            if (that.min < this.min)
+                this.min = that.min;
+            if (that.max > this.max)
+                this.max = that.max;
+            this.sum += that.sum;
+            this.count += that.count;
         }
 
-        public String measurements() {
+        private String measurements() {
             // here is only executed once for each unique key, so StringBuilder creation doesn't harm
             final StringBuilder sb = new StringBuilder(14);
-            sb.append(this.min / 10.0);
-            sb.append("/");
-            sb.append(round((this.sum / 10.0) / this.count));
-            sb.append("/");
-            sb.append(this.max / 10.0);
+            sb.append(round(this.min)).append("/");
+            sb.append(round(1.0 * this.sum / this.count)).append("/");
+            sb.append(round(this.max));
             return sb.toString();
         }
     }
 
     // Inspired by @spullara - customized hashmap on purpose
-    // The main difference is we hold only one array instead of two
-    static class RecordMap {
+    // The main difference is we hold only one array instead of two, fewer objects is faster
+    private static final class RecordMap {
 
-        static final int SIZE = 1 << 15; // 32k - bigger bucket size less collisions
-        static final int BITMASK = SIZE - 1;
-        Record[] keys = new Record[SIZE];
+        // Bigger bucket size less collisions, but you have to find a sweet spot otherwise it is becoming slower.
+        // Also works good enough for 10K stations
+        private static final int SIZE = 1 << 14; // 16kb - enough for 10K
+        private static final int BITMASK = SIZE - 1;
+        private final Record[] keys = new Record[SIZE];
 
-        static int hashBucket(int hash) {
+        // int collision;
+
+        private boolean hasNoRecord(int index) {
+            return this.keys[index] == null;
+        }
+
+        private Record getRecord(int index) {
+            return this.keys[index];
+        }
+
+        private static int hashBucket(int hash) {
             hash = hash ^ (hash >>> 16); // naive bit spreading but surprisingly decreases collision :)
             return hash & BITMASK; // fast modulo, to find bucket
         }
 
-        void putAndCollect(long segment, int start, int length, int hash, int temp) {
-            int bucket = hashBucket(hash);
-            Record existing = this.keys[bucket];
-            if (existing == null) {
-                this.keys[bucket] = new Record(segment, start, length, hash)
-                        .collect(temp);
+        private void putAndCollect(int hash, int temp, long start, int length, long word1, long word2, long wordLast) {
+            final int bucket = hashBucket(hash);
+            if (hasNoRecord(bucket)) {
+                this.keys[bucket] = new Record(start, length, word1, word2, wordLast, hash, temp);
                 return;
             }
 
-            if (!existing.equals(segment, start, length, hash)) {
-                // collision, linear probing to find a slot
-                while ((existing = this.keys[++bucket & BITMASK]) != null && !existing.equals(segment, start, length, hash)) {
-                    // can be stuck here if all the buckets are full :(
-                    // However, since the data set is max 10K (unique) this shouldn't happen
-                    // So, I'm happily leave here branchless :)
-                }
-                if (existing == null) {
-                    this.keys[bucket & BITMASK] = new Record(segment, start, length, hash)
-                            .collect(temp);
-                    return;
-                }
+            Record existing = getRecord(bucket);
+            if (existing.equals(start, word1, word2, wordLast, length)) {
                 existing.collect(temp);
+                return;
             }
-            else {
-                existing.collect(temp);
+
+            // collision++;
+            // find possible slot by scanning the slot linked list
+            while (existing.next != null) {
+                if (existing.next.equals(start, word1, word2, wordLast, length)) {
+                    existing.next.collect(temp);
+                    return;
+                }
+                existing = existing.next; // go on to next
+                // collision++;
             }
+            existing.next = new Record(start, length, word1, word2, wordLast, hash, temp);
         }
 
-        void putOrMerge(Record key) {
-            int bucket = hashBucket(key.hash);
-            Record existing = this.keys[bucket];
-            if (existing == null) {
+        private void putOrMerge(Record key) {
+            final int bucket = hashBucket(key.hash);
+            if (hasNoRecord(bucket)) {
+                key.next = null;
                 this.keys[bucket] = key;
                 return;
             }
 
-            if (!existing.equals(key)) {
-                // collision, linear probing to find a slot
-                while ((existing = this.keys[++bucket & BITMASK]) != null && !existing.equals(key)) {
-                    // can be stuck here if all the buckets are full :(
-                    // However, since the data set is max 10K (unique keys) this shouldn't happen
-                    // So, I'm happily leave here branchless :)
-                }
-                if (existing == null) {
-                    this.keys[bucket & BITMASK] = key;
-                    return;
-                }
+            Record existing = getRecord(bucket);
+            if (existing.equals(key)) {
                 existing.merge(key);
+                return;
             }
-            else {
-                existing.merge(key);
+
+            // collision++;
+            // find possible slot by scanning the slot linked list
+            while (existing.next != null) {
+                if (existing.next.equals(key)) {
+                    existing.next.merge(key);
+                    return;
+                }
+                existing = existing.next; // go on to next
+                // collision++;
             }
+            key.next = null;
+            existing.next = key;
         }
 
-        void forEach(Consumer<Record> consumer) {
+        private void forEach(Consumer<Record> consumer) {
             int pos = 0;
             Record key;
-            while (pos < this.keys.length) {
+            while (pos < SIZE) {
                 if ((key = this.keys[pos++]) == null) {
                     continue;
                 }
+                Record next = key.next;
                 consumer.accept(key);
+                while (next != null) { // also traverse the records in the collision list
+                    final Record tmp = next.next;
+                    consumer.accept(next);
+                    next = tmp;
+                }
             }
         }
 
-        void merge(RecordMap other) {
+        private void merge(RecordMap other) {
             other.forEach(this::putOrMerge);
         }
 
     }
 
     // One actor for one thread, no synchronization
-    static class RegionActor {
-
-        final FileChannel channel;
-        final long startPos;
-        final int size;
-        final RecordMap map = new RecordMap();
-        long segmentAddress;
-        int position;
-        Thread runner; // each actor has its own thread
-
-        public RegionActor(FileChannel channel, long startPos, int size) {
-            this.channel = channel;
+    private static final class RegionActor extends Thread {
+
+        private final long startPos; // start of region memory address
+        private final int size;
+
+        private final RecordMap map = new RecordMap();
+
+        public RegionActor(long startPos, int size) {
             this.startPos = startPos;
             this.size = size;
         }
 
-        void accumulate() {
-            this.runner = new Thread(() -> {
-                try {
-                    // get the segment memory address, this is the only thing we need for Unsafe
-                    this.segmentAddress = this.channel.map(FileChannel.MapMode.READ_ONLY, this.startPos, this.size, Arena.global()).address();
-                }
-                catch (IOException e) {
-                    // no-op - skip intentionally, no handling for the purpose of this challenge
-                }
-
-                int start;
-                int keyHash;
-                int length;
-                while (this.position < this.size) {
-                    byte b;
-                    start = this.position; // save line start position
-                    keyHash = UNSAFE.getByte(this.segmentAddress + this.position++); // first byte is guaranteed not to be ';'
-                    length = 1; // min key length
-                    while ((b = UNSAFE.getByte(this.segmentAddress + this.position++)) != ';') { // read until semicolon
-                        keyHash = calculateHash(keyHash, b); // calculate key hash ahead, eleminates one more loop later
-                        length++;
-                    }
+        private static long getWord(long address) {
+            return UNSAFE.getLong(address);
+        }
 
-                    final int temp = readTemperature();
-                    this.map.putAndCollect(this.segmentAddress, start, length, keyHash, temp);
+        // hasvalue & haszero
+        // adapted from https://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord
+        private static long hasSemicolon(long word) {
+            // semicolon pattern
+            final long hasVal = word ^ 0x3B3B3B3B3B3B3B3BL; // hasvalue
+            return ((hasVal - 0x0101010101010101L) & ~hasVal & 0x8080808080808080L); // haszero
+        }
 
-                    this.position++; // skip linebreak
-                }
-            });
-            this.runner.start();
+        private static int semicolonPos(long hasVal) {
+            return Long.numberOfTrailingZeros(hasVal) >>> 3;
         }
 
-        static int calculateHash(int hash, int b) {
-            return 31 * hash + b;
+        private static int decimalPos(long numberWord) {
+            return Long.numberOfTrailingZeros(~numberWord & 0x10101000);
         }
 
-        // 1. Inspired by @yemreinci - Reading temparature value without Double.parse
-        // 2. Inspired by @obourgain - Fetching first 4 bytes ahead, then masking
-        int readTemperature() {
-            int temp = 0;
-            // read 4 bytes ahead
-            final int first4 = UNSAFE.getInt(this.segmentAddress + this.position);
-            this.position += 3;
+        private static final int MAX_INNER_LOOP_SIZE = 11;
 
-            final byte b1 = (byte) first4; // first byte
-            final byte b2 = (byte) ((first4 >> 8) & 0xFF); // second byte
-            final byte b3 = (byte) ((first4 >> 16) & 0xFF); // third byte
-            if (b1 == '-') {
-                if (b3 == '.') {
-                    temp -= 10 * (b2 - '0') + (byte) ((first4 >> 24) & 0xFF) - '0'; // fourth byte
-                    this.position++;
-                }
-                else {
-                    this.position++; // skip dot
-                    temp -= 100 * (b2 - '0') + 10 * (b3 - '0') + UNSAFE.getByte(this.segmentAddress + this.position++) - '0'; // fifth byte
-                }
-            }
-            else {
-                if (b2 == '.') {
-                    temp = 10 * (b1 - '0') + b3 - '0';
+        @Override
+        public void run() {
+            long pointer = this.startPos;
+            final long size = pointer + this.size;
+            while (pointer < size) { // line start
+                long hash = 0; // reset hash
+                long s; // semicolon check word
+                final int pos; // semicolon position
+                long word1 = getWord(pointer);
+                if ((s = hasSemicolon(word1)) != 0) {
+                    pos = semicolonPos(s);
+                    // read temparature
+                    final long numberWord = getWord(pointer + pos + 1);
+                    final int decimalPos = decimalPos(numberWord);
+                    final int temp = convertIntoNumber(decimalPos, numberWord);
+
+                    word1 = partial(word1, pos); // last word
+                    this.map.putAndCollect(completeHash(hash, word1), temp, pointer, pos, word1, 0, 0);
+
+                    pointer += pos + (decimalPos >>> 3) + 4;
                 }
                 else {
-                    temp = 100 * (b1 - '0') + 10 * (b2 - '0') + (byte) ((first4 >> 24) & 0xFF) - '0'; // fourth byte
-                    this.position++;
+                    long word2 = getWord(pointer + 8);
+                    if ((s = hasSemicolon(word2)) != 0) {
+                        pos = semicolonPos(s);
+                        // read temparature
+                        final int length = pos + 8;
+                        final long numberWord = getWord(pointer + length + 1);
+                        final int decimalPos = decimalPos(numberWord);
+                        final int temp = convertIntoNumber(decimalPos, numberWord);
+
+                        word2 = partial(word2, pos); // last word
+                        this.map.putAndCollect(completeHash(hash, word1, word2), temp, pointer, length, word1, word2, 0);
+
+                        pointer += length + (decimalPos >>> 3) + 4; // seek to the line end
+                    }
+                    else {
+                        long word = 0;
+                        int length = 16;
+                        hash = appendHash(hash, word1, word2);
+                        // Let the compiler know the loop size ahead
+                        // Then it's automatically unrolled
+                        // Max key length is 13 longs, 2 we've read before, 11 left
+                        for (int i = 0; i < MAX_INNER_LOOP_SIZE; i++) {
+                            if ((s = hasSemicolon((word = getWord(pointer + length)))) != 0) {
+                                break;
+                            }
+                            hash = appendHash(hash, word);
+                            length += 8;
+                        }
+
+                        pos = semicolonPos(s);
+                        length += pos;
+                        // read temparature
+                        final long numberWord = getWord(pointer + length + 1);
+                        final int decimalPos = decimalPos(numberWord);
+                        final int temp = convertIntoNumber(decimalPos, numberWord);
+
+                        word = partial(word, pos); // last word
+                        this.map.putAndCollect(completeHash(hash, word), temp, pointer, length, word1, word2, word);
+
+                        pointer += length + (decimalPos >>> 3) + 4; // seek to the line end
+                    }
                 }
             }
+        }
+
+        // Hashes are calculated by a Mersenne Prime (1 << 7) -1
+        // This is faster than multiplication in some machines
+        private static long appendHash(long hash, long word) {
+            return (hash << 7) - hash + word;
+        }
+
+        private static long appendHash(long hash, long word1, long word2) {
+            hash = (hash << 7) - hash + word1;
+            return (hash << 7) - hash + word2;
+        }
+
+        private static int completeHash(long hash, long partial) {
+            hash = (hash << 7) - hash + partial;
+            return (int) (hash ^ (hash >>> 25));
+        }
+
+        private static int completeHash(long hash, long word1, long word2) {
+            hash = (hash << 7) - hash + word1;
+            hash = (hash << 7) - hash + word2;
+            return (int) hash ^ (int) (hash >>> 25);
+        }
 
-            return temp;
+        // Credits to @merrykitty. Magical solution to parse temparature values branchless!
+        // Taken as without modification, comments belong to @merrykitty
+        private static int convertIntoNumber(int decimalSepPos, long numberWord) {
+            final int shift = 28 - decimalSepPos;
+            // signed is -1 if negative, 0 otherwise
+            final long signed = (~numberWord << 59) >> 63;
+            final long designMask = ~(signed & 0xFF);
+            // Align the number to a specific position and transform the ascii code
+            // to actual digit value in each byte
+            final long digits = ((numberWord & designMask) << shift) & 0x0F000F0F00L;
+            // Now digits is in the form 0xUU00TTHH00 (UU: units digit, TT: tens digit, HH: hundreds digit)
+            // 0xUU00TTHH00 * (100 * 0x1000000 + 10 * 0x10000 + 1) =
+            // 0x000000UU00TTHH00 +
+            // 0x00UU00TTHH000000 * 10 +
+            // 0xUU00TTHH00000000 * 100
+            // Now TT * 100 has 2 trailing zeroes and HH * 100 + TT * 10 + UU < 0x400
+            // This results in our value lies in the bit 32 to 41 of this product
+            // That was close :)
+            final long absValue = ((digits * 0x640a0001) >>> 32) & 0x3FF;
+            final long value = (absValue ^ signed) - signed;
+            return (int) value;
         }
 
         /**
          * blocks until the map is fully collected
          */
-        RecordMap get() throws InterruptedException {
-            this.runner.join();
+        private RecordMap get() throws InterruptedException {
+            join();
             return this.map;
         }
     }
 
     private static double round(double value) {
-        return Math.round(value * 10.0) / 10.0;
+        return Math.round(value) / 10.0;
     }
 
     /**
      * Scans the given buffer to the left
      */
-    private static long findClosestLineEnd(long start, int size, FileChannel channel) throws IOException {
-        final long position = start + size;
-        final long left = Math.max(position - 101, 0);
-        final ByteBuffer buffer = ByteBuffer.allocate(101); // enough size to find at least one '\n'
-        if (channel.read(buffer.clear(), left) != -1) {
-            int bufferPos = buffer.position() - 1;
-            while (buffer.get(bufferPos) != '\n') {
-                bufferPos--;
-                size--;
-            }
+    private static long findClosestLineEnd(long start, int size) {
+        long position = start + size;
+        while (UNSAFE.getByte(--position) != '\n') {
+            // read until a linebreak
+            size--;
         }
         return size;
     }
 
-    public static void main(String[] args) throws IOException, InterruptedException {
+    private static boolean isWorkerProcess(String[] args) {
+        return Arrays.asList(args).contains("--worker");
+    }
+
+    private static void runAsWorker() throws Exception {
+        final ProcessHandle.Info info = ProcessHandle.current().info();
+        final List<String> commands = new ArrayList<>();
+        info.command().ifPresent(commands::add);
+        info.arguments().ifPresent(args -> commands.addAll(Arrays.asList(args)));
+        commands.add("--worker");
+
+        new ProcessBuilder()
+                .command(commands)
+                .start()
+                .getInputStream()
+                .transferTo(System.out);
+    }
+
+    public static void main(String[] args) throws Exception {
 
-        var concurrency = Runtime.getRuntime().availableProcessors();
+        // Dased on @thomaswue's idea, to cut unmapping delay.
+        // Strangely, unmapping delay doesn't occur on macOS/M1 however in Linux/AMD it's substantial - ~200ms
+        if (!isWorkerProcess(args)) {
+            runAsWorker();
+            return;
+        }
+
+        var concurrency = 2 * Runtime.getRuntime().availableProcessors();
         final long fileSize = Files.size(FILE);
         long regionSize = fileSize / concurrency;
 
@@ -353,30 +478,36 @@ public class CalculateAverage_yavuztas {
 
         long startPos = 0;
         final FileChannel channel = (FileChannel) Files.newByteChannel(FILE, StandardOpenOption.READ);
+        // get the memory address, this is the only thing we need for Unsafe
+        final long memoryAddress = channel.map(FileChannel.MapMode.READ_ONLY, startPos, fileSize, Arena.global()).address();
+
         final RegionActor[] actors = new RegionActor[concurrency];
         for (int i = 0; i < concurrency; i++) {
             // calculate boundaries
             long maxSize = (startPos + regionSize > fileSize) ? fileSize - startPos : regionSize;
             // shift position to back until we find a linebreak
-            maxSize = findClosestLineEnd(startPos, (int) maxSize, channel);
+            maxSize = findClosestLineEnd(memoryAddress + startPos, (int) maxSize);
 
-            final RegionActor region = (actors[i] = new RegionActor(channel, startPos, (int) maxSize));
-            region.accumulate();
+            final RegionActor region = (actors[i] = new RegionActor(memoryAddress + startPos, (int) maxSize));
+            region.start(); // start processing
 
             startPos += maxSize;
         }
 
-        final RecordMap output = new RecordMap(); // output to merge all regions
+        final RecordMap output = new RecordMap(); // output to merge all records
         for (RegionActor actor : actors) {
             final RecordMap partial = actor.get(); // blocks until get the result
             output.merge(partial);
+            // System.out.println("collisions: " + partial.collision);
         }
 
         // sort and print the result
         final TreeMap<String, String> sorted = new TreeMap<>();
-        output.forEach(key -> sorted.put(key.toString(), key.measurements()));
+        output.forEach(key -> {
+            sorted.put(key.toString(), key.measurements());
+        });
         System.out.println(sorted);
-
+        System.out.close(); // closing the stream will trigger the main process to pick up the output early
     }
 
 }