The Dalvik virtual machine can produce a complete dump of the contents of the virtual heap. This is very useful for debugging memory usage and looking for memory leaks. Getting at the information can be tricky, but has become easier in recent releases.
The first step is to cause the VM to dump its status, and then pull the hprof data off. The exact manner for doing so has changed over time.
There is a
runhat shell function, added by
build/envsetup.sh, that partially automates these steps. The
function changes in each release to accommodate newer behavior, so you have
to be careful that you don't use the wrong version.
You can only generate heap data on the emulator or a device with root access, because of the way the dump is initiated and where the output files go.
Get a command shell on the device:
$ adb shell
You can verify that you're running as root with the
The response should look like
uid=0(root) gid=0(root). If not,
su and try again. If
su fails, you're out
Next, ensure the target directory exists:
# mkdir /data/misc # chmod 777 /data/misc
ps or DDMS to determine the process ID of your application,
then send a
SIGUSR1 to the target process:
# kill -10 <pid>
The signal causes a GC, followed by the heap dump (to be completely accurate, they actually happen concurrently, but the results in the heap dump reflect the post-GC state). This can take a couple of seconds, so you have to watch for the GC log message to know when it's complete.
# ls /data/misc/heap-dump* # exit
ls to check the file names, then
exit to quit
the device command shell.
You should see two output files, named
.hprof-head, where BLAH is a runtime-generated value
that ensures the filename is unique. Pull them off of the device and
remove the device-side copy:
$ adb pull /data/misc/heap-dump-BLAH-BLAH.hprof tail.hprof $ adb pull /data/misc/heap-dump-BLAH-BLAH.hprof-head head.hprof $ adb shell rm /data/misc/heap-dump-BLAH-BLAH.hprof /data/misc/heap-dump-BLAH-BLAH.hprof-head
Merge them together and remove the intermediates:
$ cat head.hprof tail.hprof > dump.hprof $ rm head.hprof tail.hprof
You now have the hprof dump in
Some steps were taken to make this simpler. Notably, the two output
files are now combined for you, and a new API call was added that allows
a program to write the dump at will to a specific file. If you're not
using the API call, you still need to be on an emulator or running as root.
(For some builds, you can use
adb root to restart the adb
daemon as root.)
The basic procedure is the same as for 1.0/1.1, but only one file will
-head), and upon
completion you will see a log message that says "hprof: heap dump completed".
It looks like this in the log:
I/dalvikvm( 289): threadid=7: reacting to signal 10 I/dalvikvm( 289): SIGUSR1 forcing GC and HPROF dump I/dalvikvm( 289): hprof: dumping VM heap to "/data/misc/heap-dump-tm1240861355-pid289.hprof-hptemp". I/dalvikvm( 289): hprof: dumping heap strings to "/data/misc/heap-dump-tm1240861355-pid289.hprof". I/dalvikvm( 289): hprof: heap dump completed, temp file removed
Summary: as above, use
to ensure the directory exists and is writable by your application.
SIGUSR1 or use the API call to initiate a dump.
adb pull <dump-file> and
adb shell rm
<dump-file> to retrieve the file and remove it from the
device. The concatenation step is not needed.
The new API is in the
When called, the VM will go through the same series of steps (GC and generate a .hprof file), but the output will be written to a file of your choice, e.g.public static void dumpHprofData(String fileName) throws IOException
/sdcard/myapp.hprof. Because you're initiating the action from within the app, and can write the file to removable storage or the app's private data area, you can do this on a device without root access.
In 1.6, features were added that allow DDMS to request a heap dump on demand, and automatically pull the result across. Select your application and click the "dump HPROF file" button.
However, 1.6 also introduced the
permission, which is required to write data to the SD card. To use
the DDMS feature, which always writes files to the SD card,
you must have a card inserted and the permission enabled in your application.
Otherwise, things are the same as they were in 1.5.
The data file format was augmented slightly from the common hprof format,
and due to licensing restrictions the modified
hat tool cannot
be distributed. A conversion tool,
hprof-conv, can be used
to strip the Android-specific portions from the output. This tool was
first included in 1.5, but will work with older versions of Android.
The converted output should work with any hprof data analyzer, including
jhat, which is available for free in the Sun JDK, and
Copyright © 2009 The Android Open Source Project