Android app cpu usage jump to 50-100% and trace show only JDWP

Question

My application started to slowdown the phone after it ran in the background for a while.

After I recorded the cpu usage, the trace file shows me that JDWP take 99% of the cpu usage on the JDWP thread which is the only thread I can see in the trace file.

Is it possible that the JDWP (that Google says is Java Debug Wire Protocol) takes so much CPU or do I have a problem with the trace file? The phone start to work slower and get warm after the cpu usage jump so I'm pretty sure the usage data is OK.

Here are 2 trace files that show only JDWP:
https://drive.google.com/file/d/0B9MtungcpihwZnl0RFIwanktMEk/view?usp=sharing

Here is an album of before, in the middle and after the recording of the trace:
https://i.stack.imgur.com/sWWOd.jpg

The output of the command adb shell top -m 5 is here:
http://pastebin.com/2FJNVvZA

Answer 1

The JDWP thread shouldn't run very much; it's the thread that handles debugger commands, including some of the stuff that your IDE does automatically.

I can't remember ever seeing it taking a lot of CPU time, but I guess it could happen if you (or, more likely, some tool) is running a lot of commands.

Otherwise, you may have found a bug in the virtual machine (ART) or the IDE/tools.

If you feel like sharing the trace file, I wouldn't mind taking a look.

UPDATE 1: I've taken a look at the files. Indeed, there are no other threads than the JDWP thread. However, it's not using a lot of CPU -- hover your cursor over the top "JDWP." block and check the Wallclock time (4.344s) vs the CPU time (0.006s). You could also switch to the "Thread time" view instead of "Wall Clock time" in the dropdown box at the top.

Here's the human-readable part of one of the trace files:

*version
3
data-file-overflow=false
clock=dual
elapsed-time-usec=4345915
num-method-calls=410
clock-call-overhead-nsec=3808
vm=dalvik
*threads
1       main
14      Thread-7700
13      Thread-7699
12      Thread-7698
11      FileObserver
10      Binder_2
9       Binder_1
8       FinalizerWatchdogDaemon
7       FinalizerDaemon
6       ReferenceQueueDaemon
5       Compiler
4       JDWP
3       Signal Catcher
2       GC
*methods
0x6da675c0      android/ddm/DdmHandleProfiling  handleChunk     (Lorg/apache/harmony/dalvik/ddmc/Chunk;)Lorg/apache/harmony/dalvik/ddmc/Chunk;  DdmHandleProfiling.java -1
0x6da673c0      android/ddm/DdmHandleProfiling  handleMPRQ      (Lorg/apache/harmony/dalvik/ddmc/Chunk;)Lorg/apache/harmony/dalvik/ddmc/Chunk;  DdmHandleProfiling.java -1
0x6da67430      android/ddm/DdmHandleProfiling  handleMPSE      (Lorg/apache/harmony/dalvik/ddmc/Chunk;)Lorg/apache/harmony/dalvik/ddmc/Chunk;  DdmHandleProfiling.java -1
0x6da67468      android/ddm/DdmHandleProfiling  handleMPSS      (Lorg/apache/harmony/dalvik/ddmc/Chunk;)Lorg/apache/harmony/dalvik/ddmc/Chunk;  DdmHandleProfiling.java -1
0x6d8b4ca0      java/nio/ByteBuffer     order   (Ljava/nio/ByteOrder;)Ljava/nio/ByteBuffer;     ByteBuffer.java 635
0x6d8b4410      java/nio/ByteBuffer     <init>  (ILjava/nio/MemoryBlock;)V      ByteBuffer.java 116
0x6d8b44f0      java/nio/ByteBuffer     wrap    ([BII)Ljava/nio/ByteBuffer;     ByteBuffer.java 108
0x6d8dd658      java/util/HashMap       get     (Ljava/lang/Object;)Ljava/lang/Object;  HashMap.java    -1
0x6d918008      java/util/Arrays        checkOffsetAndCount     (III)V  Arrays.java     1731
0x6d9913a8      org/apache/harmony/dalvik/ddmc/ChunkHandler     wrapChunk       (Lorg/apache/harmony/dalvik/ddmc/Chunk;)Ljava/nio/ByteBuffer;   ChunkHandler.java       80
0x6d9807d0      android/os/Debug        getMethodTracingMode    ()I     Debug.java      -1
0x6d981100      android/os/Debug        startMethodTracingDdms  (IIZI)V Debug.java      -1
0x6d9811a8      android/os/Debug        stopMethodTracing       ()V     Debug.java      -1
0x6da67040      android/ddm/DdmHandleHeap       handleChunk     (Lorg/apache/harmony/dalvik/ddmc/Chunk;)Lorg/apache/harmony/dalvik/ddmc/Chunk;  DdmHandleHeap.java      -1
0x6da66e78      android/ddm/DdmHandleHeap       handleHPIF      (Lorg/apache/harmony/dalvik/ddmc/Chunk;)Lorg/apache/harmony/dalvik/ddmc/Chunk;  DdmHandleHeap.java      -1
0x6d8be8d0      java/lang/Integer       equals  (Ljava/lang/Object;)Z   Integer.java    208
0x6d8be940      java/lang/Integer       hashCode        ()I     Integer.java    302
0x6d8be190      java/lang/Integer       <init>  (I)V    Integer.java    88
0x6d8be740      java/lang/Integer       valueOf (I)Ljava/lang/Integer;  Integer.java    706
0x6d8b5240      java/nio/Buffer <init>  (IILjava/nio/MemoryBlock;)V     Buffer.java     97
0x6dc2d778      org/apache/harmony/dalvik/ddmc/DdmVmInternal    heapInfoNotify  (I)Z    DdmVmInternal.java      -2
0x6d8b5ec8      org/apache/harmony/dalvik/ddmc/Chunk    <init>  (I[BII)V        Chunk.java      45
0x6d9d22a8      java/nio/ByteArrayBuffer        get     ()B     ByteArrayBuffer.java    151
0x6d9d2000      java/nio/ByteArrayBuffer        <init>  (I[BIZ)V        ByteArrayBuffer.java    41
0x6d9d2038      java/nio/ByteArrayBuffer        <init>  ([B)V   ByteArrayBuffer.java    -1
0x6d8b5fe0      org/apache/harmony/dalvik/ddmc/DdmServer        dispatch        (I[BII)Lorg/apache/harmony/dalvik/ddmc/Chunk;   DdmServer.java  143
0x6d8b7128      dalvik/system/VMDebug   getMethodTracingMode    ()I     VMDebug.java    -2
0x6d8b7550      dalvik/system/VMDebug   startMethodTracingDdms  (IIZI)V VMDebug.java    182
0x6d8b76d8      dalvik/system/VMDebug   stopMethodTracing       ()V     VMDebug.java    -2
0x6d8ba1b8      java/lang/Number        <init>  ()V     Number.java     33
*end

As you can see, the other threads are at least present in the header.

The header contains no references to non-system methods.

I won't say it's impossible that you've found some weird bug -- but I think it's more likely that your app was completely idle at this point, except for the minor work of answering the trace commands over JDWP, and the JDWP-only trace managed to confuse you a bit.

Your title mentions "50-100% cpu usage", though, which suggests that something is running. It's unclear to me from where you got those numbers -- maybe they include everything, not just your app? Try running adb shell top -m 5 to find out the top CPU consumers in your system.