docs/html/tools/debugging/ddms.jd

page.title=Using DDMS
parent.title=Debugging
parent.link=index.html
@jd:body

 <div id="qv-wrapper">
    <div id="qv">
      <h2>In this document</h2>

      <ol>
      <li><a href="#running">Running DDMS</a></li>
        <li><a href="#how-ddms-works">How DDMS Interacts with a Debugger</a></li>

        <li><a href="#using-ddms">Using DDMS</a>
        <ol>
                <li><a href="#heap">Viewing heap usage for a process</a></li>
                <li><a href="#alloc">Tracking memory allocation of objects</a></li>
                <li><a href="#emulator">Working with an emulator or device's file system</a></li>
                <li><a href="#thread">Examining thread information</a></li>
                <li><a href="#profiling">Starting method profiling</a></li>
                <li><a href="#network">Using the Network Traffic tool</a></li>
                <li><a href="#logcat">Using LogCat</a></li>
                <li><a href="#ops-location">Emulating phone operations and location</a></li>
            </ol>

        </li>
      </ol>
    </div>
  </div>

  <p>Android Studio includes a debugging tool called the Dalvik Debug Monitor Server (DDMS), which
  provides port-forwarding services, screen capture on the device, thread and heap information on
  the device, logcat, process, and radio state information, incoming call and SMS spoofing,
  location data spoofing, and more. This page provides a modest discussion of DDMS features; it is
  not an exhaustive exploration of all the features and capabilities.</p>

  <h2 id="running">Running DDMS</h2>
  <p>DDMS is integrated into Android Studio. To use it, launch the
  <a href="{@docRoot}tools/help/monitor.html">Android Device Monitor</a>, and click the
  <strong>DDMS</strong> menu button. DDMS works with both the emulator and a
  connected device. If both are connected and running simultaneously, DDMS defaults to the emulator.</p>


  <h2 id="how-ddms-works">How DDMS Interacts with a Debugger</h2>

  <p>On Android, every application runs in its own process, each of which runs in its own virtual machine
  (VM). Each VM exposes a unique port that a debugger can attach to.</p>

  <p>When DDMS starts, it connects to <a href="{@docRoot}tools/help/adb.html">adb</a>.
  When a device is connected, a VM monitoring service is created between
  <code>adb</code> and DDMS, which notifies DDMS when a VM on the device is started or terminated. Once a VM
  is running, DDMS retrieves the VM's process ID (pid), via <code>adb</code>, and opens a connection to the
  VM's debugger, through the adb daemon (adbd) on the device. DDMS can now talk to the VM using a
  custom wire protocol.</p>

  <p>DDMS assigns a debugging port to each VM on the device. Typically,
  DDMS assigns port 8600 for the first debuggable VM, the next on 8601, and so on. When a debugger
  connects to one of these ports, all traffic is forwarded to the debugger from the associated
  VM. You can only attach a single debugger to a single port, but DDMS can handle multiple, attached
  debuggers.</p>

  <p>By default, DDMS also listens on another debugging port, the DDMS "base port" (8700, by default).
  The base port is a port forwarder, which can accept VM traffic from any debugging port and forward
  it to the debugger on port 8700. This allows you to attach one debugger to port 8700, and debug
  all the VMs on a device. The traffic that is forwarded is determined by the currently selected process
  in the DDMS Devices view.</p>

  <p>The following screenshot shows a typical DDMS screen. If you are starting DDMS from
  the command line, the screen is slightly different, but much of the functionality is identical.
  Notice that the highlighted process, <code>com.android.email</code>, that is running in the emulator
  has the debugging port 8700 assigned to it as well as 8606. This signifies that DDMS is currently
  forwarding port 8606 to the static debugging port of 8700.</p>

  <img src="{@docRoot}images/debug-ddms.png"
       width="1024" />
  <p class="img-caption"><strong>Figure 1.</strong>
  Screenshot of DDMS</p>

  <p>If you are using the command line, read <a href=
  "{@docRoot}tools/debugging/debugging-projects-cmdline.html#debuggingPort">Configuring
  your IDE to attach to the debugging port</a>, for more information on attaching your
  debugger.</p>

  <p class="note"><strong>Tip:</strong> You can set a number of DDMS preferences in
  <strong>File</strong> &gt; <strong>Preferences</strong>. Preferences are saved to
  <code>$HOME/.android/ddms.cfg</code>.</p>

  <p class="warning"><strong>Known debugging issues with Dalvik</strong><br />
  Debugging an application in the Dalvik VM should work the same as it does in other VMs. However,
  when single-stepping out of synchronized code, the "current line" cursor may jump to the last
  line in the method for one step.</p>

  <h2 id="using-ddms">Using DDMS</h2>
  The following sections describe how to use DDMS and the various tabs and panes that are part of the
  DDMS GUI. The Android Studio version and the command line version have minor UI differences, but
  the same functionality. For information on running DDMS, see the previous section in this document,
  <a href="#running">Running DDMS</a>.


  <h3 id="heap">Viewing heap usage for a process</h3>

  <p>DDMS allows you to view how much heap memory a process is using. This information is useful in
  tracking heap usage at a certain point of time during the execution of your application.</p>
  <p>To view heap usage for a process:</p>
  <ol>
    <li>In the Devices tab, select the process that you want to see the heap information for.</li>

    <li>Click the <strong>Update Heap</strong> button to enable heap information for the
    process.</li>

    <li>In the Heap tab, click <strong>Cause GC</strong> to invoke garbage collection, which
    enables the collection of heap data. When the operation completes, you will see a group of
    object types and the memory that has been allocated for each type. You can click <strong>Cause
    GC</strong> again to refresh the data.</li>

    <li>Click on an object type in the list to see a bar graph that shows the number of objects
    allocated for a particular memory size in bytes.</li>
  </ol>

  <h3 id="alloc">Tracking memory allocation of objects</h3>

  <p>DDMS provides a feature to track objects that are being allocated to memory and to see which
  classes and threads are allocating the objects. This allows you to track, in real time, where
  objects are being allocated when you perform certain actions in your application. This
  information is valuable for assessing memory usage that can affect application performance.
  </p>

  <p>To track memory allocation of objects:</p>
  <ol>
    <li>In the Devices tab, select the process that you want to enable allocation tracking
    for.</li>

    <li>In the Allocation Tracker tab, click the <strong>Start Tracking</strong> button to begin
    allocation tracking. At this point, anything you do in your application will be tracked.</li>

    <li>Click <strong>Get Allocations</strong> to see a list of objects that have been allocated
    since you clicked on the <strong>Start Tracking</strong> button. You can click on <strong>Get
    Allocations</strong> again to append to the list new objects that have been
    allocated.</li>

    <li>To stop tracking or to clear the data and start over, click the <strong>Stop Tracking
    button</strong>.</li>

    <li>Click on a specific row in the list to see more detailed information such as the method and
    line number of the code that allocated the object.</li>
  </ol>

  <h3 id="emulator">Working with an emulator or device's file system</h3>

  <p>DDMS provides a File Explorer tab that allows you to view, copy, and delete files on the
  device. This feature is useful in examining files that are created by your application or if you
  want to transfer files to and from the device.</p>

  <p>To work with an emulator or device's file system:</p>
  <ol>
    <li>In the Devices tab, select the emulator that you want to view the file system for.</li>

    <li>To copy a file from the device, locate the file in the File Explorer and click the
    <strong>Pull file</strong> button.</li>

    <li>To copy a file to the device, click the <strong>Push file</strong> button on the File
    Explorer tab.</li>
  </ol>

  <!-- Need to elaborate more on where things are stored in the file system,
   databases, apks, user info, files that are important to look at -->

  <h3 id="thread">Examining thread information</h3>

  <p>The Threads tab in DDMS shows you the currently running threads for a selected process.</p>

  <ol>
    <li>In the Devices tab, select the process that you want to examine the threads for.</li>

    <li>Click the <strong>Update Threads</strong> button.</li>

    <li>In the Threads tab, you can view the thread information for the selected process.</li>
  </ol>

  <h3 id="profiling">Starting method profiling</h3>

  <p>Method profiling is a means to track certain metrics about a method, such as number of calls,
  execution time, and time spent executing the method. If you want more granular control over 
  where profiling data is collected, use the {@link android.os.Debug#startMethodTracing()} and 
  {@link android.os.Debug#stopMethodTracing()} methods. For more information about generating trace logs, see 
  <a href="debugging-tracing.html">Profiling and Debugging UIs</a>.</p>

  <p>Before you start method profiling in DDMS, be aware of the following restrictions:</p>
    <ul>
      <li>Android 2.1 and earlier devices must
      have an SD card present and your application must have permission to write to the SD card.
      <li>Android 2.2 and later devices do not need an SD card. The trace log files are 
      streamed directly to your development machine.</li>
    </ul>

  <p>To start method profiling:</p>
  <ol>
    <li>On the Devices tab, select the process that you want to enable method profiling for.</li>

    <li>Click the <strong>Start Method Profiling</strong> button.</li>

    <li>In Android 4.4 and later, choose either trace-based profiling or sample-based profiling
    with a specified sampling interval. For earlier versions of Android, only trace-based profiling
    is available.</li>

    <li>Interact with your application to start the methods that you want to profile.</li>

    <li>Click the <strong>Stop Method Profiling</strong> button. DDMS stops profiling your
    application and opens <a href="{@docRoot}tools/debugging/debugging-ui.html">Traceview</a>
    with the method profiling information that was collected
    between the time you clicked on <strong>Start Method Profiling</strong> and <strong>Stop Method
    Profiling</strong>.</li>
  </ol>

   <h3 id="network">Using the Network Traffic tool</h3>

   <p>In Android 4.0, the DDMS (Dalvik Debug Monitor Server) includes a Detailed
Network Usage tab that makes it possible to track when your application is
making network requests. Using this tool, you can monitor how and when your app
transfers data and optimize the underlying code appropriately. You can also
distinguish between different traffic types by applying a “tag” to network
sockets before use.</p>

<p>These tags are shown in a stack area chart in DDMS, as shown in figure 2:</p>

<img src="{@docRoot}images/developing/ddms-network.png" />
<p class="img-caption"><strong>Figure 2.</strong> Network Usage tab.</p>

<p>By monitoring the frequency of your data transfers, and the amount of data
transferred during each connection, you can identify areas of your application
that can be made more battery-efficient. Generally, you should look for
short spikes that can be delayed, or that should cause a later transfer to be
pre-empted. </p>

<p>To better identify the cause of transfer spikes, the
{@link android.net.TrafficStats} API allows you
to tag the data transfers occurring within a thread using {@link
android.net.TrafficStats#setThreadStatsTag setThreadStatsTag()}, followed
by manually tagging (and untagging) individual sockets using {@link
android.net.TrafficStats#tagSocket tagSocket()} and {@link
android.net.TrafficStats#untagSocket untagSocket()}. For example:</p>

<pre>TrafficStats.setThreadStatsTag(0xF00D);
TrafficStats.tagSocket(outputSocket);
// Transfer data using socket
TrafficStats.untagSocket(outputSocket);</pre>

<p>Alternatively, the {@link java.net.URLConnection} APIs included in the platform
automatically tag sockets internally based on the active tag (as identified by 
{@link android.net.TrafficStats#getThreadStatsTag getThreadStatsTag()}).
These APIs correctly tag/untag sockets when recycled through
keep-alive pools. In the following example,  
{@link android.net.TrafficStats#setThreadStatsTag setThreadStatsTag()} 
sets the active tag to be {@code 0xF00D}. 
There can only be one active tag per thread. 
That is the value that will 
be returned by {@link android.net.TrafficStats#getThreadStatsTag getThreadStatsTag()}
and thus used by the HTTP client to tag sockets. The {@code finally} statement 
invokes 
{@link android.net.TrafficStats#clearThreadStatsTag clearThreadStatsTag()} 
to clear the tag.</p>

<pre>TrafficStats.setThreadStatsTag(0xF00D);
    try {
        // Make network request using your http client.
    } finally {
        TrafficStats.clearThreadStatsTag();
}</pre>

<p>Socket tagging is supported in Android 4.0, but real-time stats will only be
displayed on devices running Android 4.0.3 or higher.</p>

  <h3 id="logcat">Using LogCat</h3>

  <p>LogCat is integrated into DDMS, and outputs the messages that you print out using the {@link android.util.Log}
  class along with other system messages such as stack traces when exceptions are thrown. View the
  <a href="{@docRoot}tools/debugging/debugging-log.html">Reading and
  Writing Log Messages.</a> topic for more information on how to log messages to the LogCat.</p>

  <p>When you have set up your logging, you can use the LogCat feature of DDMS to filter certain
  messages with the following buttons:</p>

  <ul>
    <li>Verbose</li>

    <li>Debug</li>

    <li>Info</li>

    <li>Warn</li>

    <li>Error</li>
  </ul>

  <p>You can also setup your own custom filter to specify more details such as filtering messages
  with the log tags or with the process id that generated the log message. The add filter,
  edit filter, and delete filter buttons let you manage your custom filters.</p>

  <h3 id="ops-location">Emulating phone operations and location</h3>
  <p>The Emulator control tab lets you simulate a
  phone's voice and data network status. This is useful when you want to test your application's
  robustness in differing network environments.</p>

  <h4>Changing network state, speed, and latency</h4>
  <p>The Telephony Status section of the Emulator
  controls tab lets you change different aspects of the phone's networks status, speed and latency.
  The following options are available to you and are effective immediately after you set them:</p>

  <ul>
    <li>Voice - unregistered, home, roaming, searching, denied</li>

    <li>Data - unregistered, home, roaming, searching, denied</li>

    <li>Speed - Full, GSM, HSCSD, GPRS, EDGE, UMTS, HSDPA</li>

    <li>Latency - GPRS, EDGE, UMTS</li>
  </ul>

  <h4>Spoofing calls or SMS text messages</h4>
  <p>The Telephony Actions section of the Emulator
  controls tab lets you spoof calls and messages. This is useful when you want to to test your
  application's robustness in responding to incoming calls and messages that are sent to the phone.
  The following actions are available to you:</p>

  <ul>
    <li>Voice - Enter a number in the <strong>Incoming number</strong> field and click 
    <strong>Call</strong> to send a simulated call to the emulator or phone. Click the
    <strong>Hang up</strong> button to terminate the call.</li>

    <li>SMS - Enter a number in the <strong>Incoming number</strong> field and a message in the
    <strong>Message:</strong> field and click the <strong>Send</strong> button to send the
    message.</li>
  </ul>

  <h4>Setting the location of the phone</h4>
  <p>If your application depends on the location of the phone, you can have DDMS send your
  device or AVD a mock location. This is useful if you
  want to test different aspects of your application's location specific features without
  physically moving. The following geolocation data types are available to you:</p>

  <ul>
    <li>Manual - set the location by manually specifying decimal or sexagesimal longitude and
    latitude values.</li>

    <li>GPX - GPS eXchange file</li>

    <li>KML - Keyhole Markup Language file</li>
  </ul>

  For more information about providing mock location data, see 
  <a href="{@docRoot}guide/topics/location/strategies.html#MockData">Location Strategies</a>.