@trustin good idea... will you work on this ?
 Just a proposal : why not using uuid (real one) such that unicity is provable ?
 Note: not uuid from jvm but another implementation...
 Yeah, we can do that, too.  3.x had to work with Java 5 which did not have access to the hardware address of the network interface, but the minimum requirement of 4.x is Java 6, so we can definitely do that.
 I think we can even use the UUID from JDK as long as we feed all the fields by ourselves.
 @trustin you will take care?
 the id can  be everything,Long or String ,I think there is no need to insist it as an Integer
 From my own research, what I've found on various implementation as probably the best is the following combination in UUID:
- partial MAC address (to ensure difference between 2 hosts), set statically at the beginning of the JVM
- a JVM PID (to ensure difference between 2 JVM on the same host), set statically at the beginning of the JVM
- partial timestamp in ms (since nano is not always implemented and so last bytes are just 0, and since most of the front bytes are 0)
- and finally a counter to prevent 2 same values on the same ms (as AtomicLong) (this is the tricker part I've found that ensures that 2 immediate consecutive or simultaneous demands of UUID are still different)

My 2 cents...
 like hepin1989 said, id should be anything,

to me:
- channel.id() should return an java.lang.Object (or maybe a <T> T to avoid cast ?)
- it should be allowed for user to provide a certain implementation for a "ChannelIdGenerator" interface with a given "public Object generateId(Channel channel)" method to implements
- the default proposed netty channel id strategy should implement this interface

As for the implementation detail of the id, I think fredericBregier have a good point.
Maybe also looking on how jgroups and/or infinispan generate their unique cluster id could be helpful ?
 @trustin @normanmaurer 

UUID    maybe human unreadable  .....
 I think there is no need for make it human readable

Am 21.09.2013 um 18:06 schrieb yaphet notifications@github.com:

> @trustin @normanmaurer
> 
> UUID maybe human unreadable .....
> 
> —
> Reply to this email directly or view it on GitHub.
 mostly,we using the channel as a key for the map<channelId，channel>,why should it be human readable？

Could you commit this as a separate thing as it's not related ?
 I find this naming a bit confusing as from the naming I would expect to have a short returned. Same goes for the user where I would expect long
 why transient ?
 Serialization.
 Ah missed that it extends Serializable... makes sense.
 Renamed to `asShort/LongText()`
 Done.

Resurrect Channel.id()
If we don't insist the type of `Channel.id()` to be an integer, I think we might be able to make it unique for sure.  For example, it could be `hashCode` + `identityHashCode` + `nanoTime` + `sequence`.  Practically, this should never collide.

buffer/src/main/java/io/netty/buffer/ByteBufUtil.java transport/src/main/java/io/netty/channel/AbstractChannel.java transport/src/main/java/io/netty/channel/Channel.java
buffer/src/main/java/io/netty/buffer/ByteBufUtil.java transport/src/main/java/io/netty/channel/AbstractChannel.java transport/src/main/java/io/netty/channel/Channel.java transport/src/main/java/io/netty/channel/ChannelId.java transport/src/main/java/io/netty/channel/DefaultChannelId.java
diff --git a/buffer/src/main/java/io/netty/buffer/ByteBufUtil.java b/buffer/src/main/java/io/netty/buffer/ByteBufUtil.java
index 8860cbae740..f501ed13ca1 100644
--- a/buffer/src/main/java/io/netty/buffer/ByteBufUtil.java
+++ b/buffer/src/main/java/io/netty/buffer/ByteBufUtil.java
@@ -75,6 +75,38 @@ public static String hexDump(ByteBuf buffer, int fromIndex, int length) {
         return new String(buf);
     }
 
+    /**
+     * Returns a <a href="http://en.wikipedia.org/wiki/Hex_dump">hex dump</a>
+     * of the specified byte array.
+     */
+    public static String hexDump(byte[] array) {
+        return hexDump(array, 0, array.length);
+    }
+
+    /**
+     * Returns a <a href="http://en.wikipedia.org/wiki/Hex_dump">hex dump</a>
+     * of the specified byte array's sub-region.
+     */
+    public static String hexDump(byte[] array, int fromIndex, int length) {
+        if (length < 0) {
+            throw new IllegalArgumentException("length: " + length);
+        }
+        if (length == 0) {
+            return "";
+        }
+
+        int endIndex = fromIndex + length;
+        char[] buf = new char[length << 1];
+
+        int srcIdx = fromIndex;
+        int dstIdx = 0;
+        for (; srcIdx < endIndex; srcIdx ++, dstIdx += 2) {
+            System.arraycopy(HEXDUMP_TABLE, (array[srcIdx] & 0xFF) << 1, buf, dstIdx, 2);
+        }
+
+        return new String(buf);
+    }
+
     /**
      * Calculates the hash code of the specified buffer.  This method is
      * useful when implementing a new buffer type.
diff --git a/transport/src/main/java/io/netty/channel/AbstractChannel.java b/transport/src/main/java/io/netty/channel/AbstractChannel.java
index c04f67aa7ba..f8c6de8a2dc 100644
--- a/transport/src/main/java/io/netty/channel/AbstractChannel.java
+++ b/transport/src/main/java/io/netty/channel/AbstractChannel.java
@@ -20,7 +20,6 @@
 import io.netty.util.ReferenceCountUtil;
 import io.netty.util.internal.EmptyArrays;
 import io.netty.util.internal.PlatformDependent;
-import io.netty.util.internal.ThreadLocalRandom;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
@@ -49,7 +48,7 @@ public abstract class AbstractChannel extends DefaultAttributeMap implements Cha
     private MessageSizeEstimator.Handle estimatorHandle;
 
     private final Channel parent;
-    private final long hashCode = ThreadLocalRandom.current().nextLong();
+    private final ChannelId id = DefaultChannelId.newInstance();
     private final Unsafe unsafe;
     private final DefaultChannelPipeline pipeline;
     private final ChannelFuture succeededFuture = new SucceededChannelFuture(this, null);
@@ -79,6 +78,11 @@ protected AbstractChannel(Channel parent, EventLoop eventLoop) {
         pipeline = new DefaultChannelPipeline(this);
     }
 
+    @Override
+    public final ChannelId id() {
+        return id;
+    }
+
     @Override
     public boolean isWritable() {
         ChannelOutboundBuffer buf = unsafe.outboundBuffer();
@@ -271,7 +275,7 @@ public Unsafe unsafe() {
      */
     @Override
     public final int hashCode() {
-        return (int) hashCode;
+        return id.hashCode();
     }
 
     /**
@@ -289,21 +293,7 @@ public final int compareTo(Channel o) {
             return 0;
         }
 
-        long ret = hashCode - o.hashCode();
-        if (ret > 0) {
-            return 1;
-        }
-        if (ret < 0) {
-            return -1;
-        }
-
-        ret = System.identityHashCode(this) - System.identityHashCode(o);
-        if (ret != 0) {
-            return (int) ret;
-        }
-
-        // Jackpot! - different objects with same hashes
-        throw new Error();
+        return id().compareTo(o.id());
     }
 
     /**
@@ -331,11 +321,30 @@ public String toString() {
                 srcAddr = remoteAddr;
                 dstAddr = localAddr;
             }
-            strVal = String.format("[id: 0x%08x, %s %s %s]", (int) hashCode, srcAddr, active? "=>" : ":>", dstAddr);
+
+            StringBuilder buf = new StringBuilder(96);
+            buf.append("[id: 0x");
+            buf.append(id.asShortText());
+            buf.append(", ");
+            buf.append(srcAddr);
+            buf.append(active? " => " : " :> ");
+            buf.append(dstAddr);
+            buf.append(']');
+            strVal = buf.toString();
         } else if (localAddr != null) {
-            strVal = String.format("[id: 0x%08x, %s]", (int) hashCode, localAddr);
+            StringBuilder buf = new StringBuilder(64);
+            buf.append("[id: 0x");
+            buf.append(id.asShortText());
+            buf.append(", ");
+            buf.append(localAddr);
+            buf.append(']');
+            strVal = buf.toString();
         } else {
-            strVal = String.format("[id: 0x%08x]", (int) hashCode);
+            StringBuilder buf = new StringBuilder(16);
+            buf.append("[id: 0x");
+            buf.append(id.asShortText());
+            buf.append(']');
+            strVal = buf.toString();
         }
 
         strValActive = active;
diff --git a/transport/src/main/java/io/netty/channel/Channel.java b/transport/src/main/java/io/netty/channel/Channel.java
index 28e364f7e81..6a6adaa06a7 100644
--- a/transport/src/main/java/io/netty/channel/Channel.java
+++ b/transport/src/main/java/io/netty/channel/Channel.java
@@ -68,6 +68,11 @@
  */
 public interface Channel extends AttributeMap, ChannelOutboundInvoker, ChannelPropertyAccess, Comparable<Channel> {
 
+    /**
+     * Returns the globally unique identifier of this {@link Channel}.
+     */
+    ChannelId id();
+
     /**
      * Return the {@link EventLoop} this {@link Channel} was registered too.
      */
diff --git a/transport/src/main/java/io/netty/channel/ChannelId.java b/transport/src/main/java/io/netty/channel/ChannelId.java
new file mode 100644
index 00000000000..b62fff88812
--- /dev/null
+++ b/transport/src/main/java/io/netty/channel/ChannelId.java
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2013 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+package io.netty.channel;
+
+import java.io.Serializable;
+
+/**
+ * Represents the globally unique identifier of a {@link Channel}.
+ * <p>
+ * The identifier is generated from various sources listed in the following:
+ * <ul>
+ * <li>MAC address (EUI-48 or EUI-64) or the network adapter, preferrably a globally unique one,</li>
+ * <li>the current process ID,</li>
+ * <li>{@link System#currentTimeMillis()},</li>
+ * <li>{@link System#nanoTime()},</li>
+ * <li>a random 32-bit integer, and</li>
+ * <li>a sequentially incremented 32-bit integer.</li>
+ * </ul>
+ * </p>
+ * <p>
+ * The global uniqueness of the generated identifier mostly depends on the MAC address and the current process ID,
+ * which are auto-detected at the class-loading time in best-effort manner.  If all attempts to acquire them fail,
+ * a warning message is logged, and random values will be used instead.  Alternatively, you can specify them manually
+ * via system properties:
+ * <ul>
+ * <li>{@code io.netty.machineId} - hexadecimal representation of 48 (or 64) bit integer,
+ *     optionally separated by colon or hyphen.</li>
+ * <li>{@code io.netty.processId} - an integer between 0 and 65535</li>
+ * </ul>
+ * </p>
+ */
+public interface ChannelId extends Serializable, Comparable<ChannelId> {
+    /**
+     * Returns the short but globally non-unique string representation of the {@link ChannelId}.
+     */
+    String asShortText();
+
+    /**
+     * Returns the long yet globally unique string representation of the {@link ChannelId}.
+     */
+    String asLongText();
+}
diff --git a/transport/src/main/java/io/netty/channel/DefaultChannelId.java b/transport/src/main/java/io/netty/channel/DefaultChannelId.java
new file mode 100644
index 00000000000..2f3ae26a002
--- /dev/null
+++ b/transport/src/main/java/io/netty/channel/DefaultChannelId.java
@@ -0,0 +1,375 @@
+/*
+ * Copyright 2013 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+package io.netty.channel;
+
+import io.netty.buffer.ByteBufUtil;
+import io.netty.util.internal.SystemPropertyUtil;
+import io.netty.util.internal.ThreadLocalRandom;
+import io.netty.util.internal.logging.InternalLogger;
+import io.netty.util.internal.logging.InternalLoggerFactory;
+
+import java.lang.management.ManagementFactory;
+import java.net.NetworkInterface;
+import java.net.SocketException;
+import java.util.Arrays;
+import java.util.Enumeration;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.regex.Pattern;
+
+/**
+ * The default {@link ChannelId} implementation.
+ */
+final class DefaultChannelId implements ChannelId {
+
+    private static final long serialVersionUID = 3884076183504074063L;
+
+    private static final InternalLogger logger = InternalLoggerFactory.getInstance(DefaultChannelId.class);
+
+    private static final Pattern MACHINE_ID_PATTERN = Pattern.compile("^(?:[0-9a-fA-F][:-]?){6,8}$");
+    private static final int MACHINE_ID_LEN = 8;
+    private static final byte[] MACHINE_ID;
+    private static final int PROCESS_ID_LEN = 2;
+    private static final int MAX_PROCESS_ID = 65535;
+    private static final int PROCESS_ID;
+    private static final int SEQUENCE_LEN = 4;
+    private static final int TIMESTAMP_LEN = 8;
+    private static final int RANDOM_LEN = 4;
+
+    private static final AtomicInteger nextSequence = new AtomicInteger();
+
+    static ChannelId newInstance() {
+        DefaultChannelId id = new DefaultChannelId();
+        id.init();
+        return id;
+    }
+
+    static {
+        byte[] machineId = null;
+        String customMachineId = SystemPropertyUtil.get("io.netty.machineId");
+        if (customMachineId != null) {
+            if (MACHINE_ID_PATTERN.matcher(customMachineId).matches()) {
+                machineId = parseMachineId(customMachineId);
+                logger.debug("-Dio.netty.machineId: {} (user-set)", customMachineId);
+            } else {
+                logger.warn("-Dio.netty.machineId: {} (malformed)", customMachineId);
+            }
+        }
+
+        if (machineId == null) {
+            machineId = defaultMachineId();
+            if (logger.isDebugEnabled()) {
+                logger.debug("-Dio.netty.machineId: {} (auto-detected)", formatAddress(machineId));
+            }
+        }
+
+        MACHINE_ID = machineId;
+
+        int processId = -1;
+        String customProcessId = SystemPropertyUtil.get("io.netty.processId");
+        if (customProcessId != null) {
+            try {
+                processId = Integer.parseInt(customProcessId);
+            } catch (NumberFormatException e) {
+                // Malformed input.
+            }
+
+            if (processId < 0 || processId > MAX_PROCESS_ID) {
+                processId = -1;
+                logger.warn("-Dio.netty.processId: {} (malformed)", customProcessId);
+            } else if (logger.isDebugEnabled()) {
+                logger.debug("-Dio.netty.processId: {} (user-set)", processId);
+            }
+        }
+
+        if (processId < 0) {
+            processId = defaultProcessId();
+            if (logger.isDebugEnabled()) {
+                logger.debug("-Dio.netty.processId: {} (auto-detected)", processId);
+            }
+        }
+
+        PROCESS_ID = processId;
+    }
+
+    @SuppressWarnings("DynamicRegexReplaceableByCompiledPattern")
+    private static byte[] parseMachineId(String value) {
+        // Strip separators.
+        value = value.replaceAll("[:-]", "");
+
+        byte[] machineId = new byte[MACHINE_ID_LEN];
+        for (int i = 0; i < value.length(); i += 2) {
+            machineId[i] = (byte) Integer.parseInt(value.substring(i, i + 2), 16);
+        }
+
+        return machineId;
+    }
+
+    private static byte[] defaultMachineId() {
+        // Find the best MAC address available.
+        final byte[] NOT_FOUND = { -1 };
+        byte[] bestMacAddr = NOT_FOUND;
+
+        Enumeration<NetworkInterface> ifaces = null;
+        try {
+            ifaces = NetworkInterface.getNetworkInterfaces();
+        } catch (SocketException e) {
+            logger.warn("Failed to find the loopback interface", e);
+        }
+
+        if (ifaces != null) {
+            while (ifaces.hasMoreElements()) {
+                NetworkInterface iface = ifaces.nextElement();
+                try {
+                    if (iface.isLoopback() || iface.isPointToPoint() || iface.isVirtual()) {
+                        continue;
+                    }
+                } catch (SocketException e) {
+                    logger.debug("Failed to determine the type of a network interface: {}", iface, e);
+                    continue;
+                }
+
+                byte[] macAddr;
+                try {
+                    macAddr = iface.getHardwareAddress();
+                } catch (SocketException e) {
+                    logger.debug("Failed to get the hardware address of a network interface: {}", iface, e);
+                    continue;
+                }
+
+                if (isBetterAddress(bestMacAddr, macAddr)) {
+                    bestMacAddr = macAddr;
+                }
+            }
+        }
+
+        if (bestMacAddr == NOT_FOUND) {
+            bestMacAddr = new byte[MACHINE_ID_LEN];
+            ThreadLocalRandom.current().nextBytes(bestMacAddr);
+            logger.warn(
+                    "Failed to find a usable hardware address from the network interfaces; using random bytes: {}",
+                    formatAddress(bestMacAddr));
+        }
+
+        if (bestMacAddr.length != MACHINE_ID_LEN) {
+            bestMacAddr = Arrays.copyOf(bestMacAddr, MACHINE_ID_LEN);
+        }
+
+        return bestMacAddr;
+    }
+
+    private static boolean isBetterAddress(byte[] current, byte[] candidate) {
+        if (candidate == null) {
+            return false;
+        }
+
+        // Must be EUI-48 or longer.
+        if (candidate.length < 6) {
+            return false;
+        }
+
+        // Must not be filled with only 0 or 1.
+        boolean onlyZero = true;
+        boolean onlyOne = true;
+        for (byte b: candidate) {
+            if (b != 0) {
+                onlyZero = false;
+            }
+
+            if (b != -1) {
+                onlyOne = false;
+            }
+        }
+
+        if (onlyZero || onlyOne) {
+            return false;
+        }
+
+        // Must not be a multicast address
+        if ((candidate[0] & 1) != 0) {
+            return false;
+        }
+
+        // Prefer longer globally unique addresses.
+        if ((current[0] & 2) == 0) {
+            if ((candidate[0] & 2) == 0) {
+                return candidate.length > current.length;
+            } else {
+                return false;
+            }
+        } else {
+            if ((candidate[0] & 2) == 0) {
+                return true;
+            } else {
+                return candidate.length > current.length;
+            }
+        }
+    }
+
+    private static String formatAddress(byte[] addr) {
+        StringBuilder buf = new StringBuilder(24);
+        for (byte b: addr) {
+            buf.append(String.format("%02x:", b & 0xff));
+        }
+        return buf.substring(0, buf.length() - 1);
+    }
+
+    private static int defaultProcessId() {
+        String value = ManagementFactory.getRuntimeMXBean().getName();
+        int atIndex = value.indexOf('@');
+        if (atIndex >= 0) {
+            value = value.substring(0, atIndex);
+        }
+
+        int pid;
+        try {
+            pid = Integer.parseInt(value);
+        } catch (NumberFormatException e) {
+            pid = -1;
+        }
+
+        if (pid < 0 || pid > MAX_PROCESS_ID) {
+            pid = ThreadLocalRandom.current().nextInt(MAX_PROCESS_ID + 1);
+            logger.warn("Failed to find the current process ID; using a random value: {}",  pid);
+        }
+
+        return pid;
+    }
+
+    private final byte[] data = new byte[MACHINE_ID_LEN + PROCESS_ID_LEN + SEQUENCE_LEN + TIMESTAMP_LEN + RANDOM_LEN];
+    private int hashCode;
+
+    private transient String shortValue;
+    private transient String longValue;
+
+    public DefaultChannelId() { }
+
+    private void init() {
+        int i = 0;
+
+        // machineId
+        System.arraycopy(MACHINE_ID, 0, data, i, MACHINE_ID_LEN);
+        i += MACHINE_ID_LEN;
+
+        // processId
+        i = writeShort(i, PROCESS_ID);
+
+        // sequence
+        i = writeInt(i, nextSequence.getAndIncrement());
+
+        // timestamp (kind of)
+        i = writeLong(i, Long.reverse(System.nanoTime()) ^ System.currentTimeMillis());
+
+        // random
+        int random = ThreadLocalRandom.current().nextInt();
+        hashCode = random;
+        i = writeInt(i, random);
+
+        assert i == data.length;
+    }
+
+    private int writeShort(int i, int value) {
+        data[i ++] = (byte) (value >>> 8);
+        data[i ++] = (byte) value;
+        return i;
+    }
+
+    private int writeInt(int i, int value) {
+        data[i ++] = (byte) (value >>> 24);
+        data[i ++] = (byte) (value >>> 16);
+        data[i ++] = (byte) (value >>> 8);
+        data[i ++] = (byte) value;
+        return i;
+    }
+
+    private int writeLong(int i, long value) {
+        data[i ++] = (byte) (value >>> 56);
+        data[i ++] = (byte) (value >>> 48);
+        data[i ++] = (byte) (value >>> 40);
+        data[i ++] = (byte) (value >>> 32);
+        data[i ++] = (byte) (value >>> 24);
+        data[i ++] = (byte) (value >>> 16);
+        data[i ++] = (byte) (value >>> 8);
+        data[i ++] = (byte) value;
+        return i;
+    }
+
+    @Override
+    public String asShortText() {
+        String shortValue = this.shortValue;
+        if (shortValue == null) {
+            this.shortValue = shortValue = ByteBufUtil.hexDump(
+                    data, MACHINE_ID_LEN + PROCESS_ID_LEN + SEQUENCE_LEN + TIMESTAMP_LEN, RANDOM_LEN);
+        }
+        return shortValue;
+    }
+
+    @Override
+    public String asLongText() {
+        String longValue = this.longValue;
+        if (longValue == null) {
+            this.longValue = longValue = newLongValue();
+        }
+        return longValue;
+    }
+
+    private String newLongValue() {
+        StringBuilder buf = new StringBuilder(data.length + 4);
+        int i = 0;
+        i = appendHexDumpField(buf, i, MACHINE_ID_LEN);
+        i = appendHexDumpField(buf, i, PROCESS_ID_LEN);
+        i = appendHexDumpField(buf, i, SEQUENCE_LEN);
+        i = appendHexDumpField(buf, i, TIMESTAMP_LEN);
+        i = appendHexDumpField(buf, i, RANDOM_LEN);
+        assert i == data.length;
+        return buf.substring(0, buf.length() - 1);
+    }
+
+    private int appendHexDumpField(StringBuilder buf, int i, int length) {
+        buf.append(ByteBufUtil.hexDump(data, i, length));
+        buf.append('-');
+        i += length;
+        return i;
+    }
+
+    @Override
+    public int hashCode() {
+        return hashCode;
+    }
+
+    @Override
+    public int compareTo(ChannelId o) {
+        return 0;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj == this) {
+            return true;
+        }
+
+        if (!(obj instanceof DefaultChannelId)) {
+            return false;
+        }
+
+        return Arrays.equals(data, ((DefaultChannelId) obj).data);
+    }
+
+    @Override
+    public String toString() {
+        return asShortText();
+    }
+}
