Strange OutOfMemoryError at StringBuilder setLength(0)

Question

It seems no one has reported similar situations... I have absolutely no idea what happened...

I have a StringBuilder of size 8Mb to process a large String result. I am trying to reuse the StringBuilder. I thought setting length = 0 will just reset the counter and not allocate new memory?

try {
      //result.length() around 4Mb
        StringBuilder sBuilder = new StringBuilder(result.length());
        result = DoSomethingToResult1(sBuilder, result); //shrink result a bit using replaceAll

        try {

            sssBuilder.setLength(0);
            result = DoSomethingToResult2(sBuilder, result); //shrink result further using replaceAll
        } catch (OutOfMemoryError e) {
             Log.d(TAG, "Out of Memory on 2");
        }

        try {
            sBuilder.setLength(0);  //OutOfMemory thrown here.          
            result = DoSomethingToResult3(sBuilder, result); //shrink result even further using replaceAll
        } catch (OutOfMemoryError e) {
             Log.d(TAG, "Out of Memory on 3");
        }

    } catch (OutOfMemoryError e) {
                Log.d(TAG, "Cannot create sBuilder");
    }

The process usually dies on the second setLength(0), sometimes dies on the first setLength(0), but it can always create the sBuilder in the beginning.

In DoSomethingToResult, I split result into chunk of 100Kb size and append to sBuilder one by one, returning sBuilder.toString(). So problem does not come from replaceAll. And since it passed the first process, I don't think the toString() is the problem either.

I tried:

sBuilder.setLength(0);
System.gc();
try{
    Thread.sleep(1000);
}catch(Exception e){};

or

System.gc();
try{
    Thread.sleep(1000);
}catch(Exception e){};
sBuilder.setLength(0);

Both failed.

Log output:

E/dalvikvm-heap(27130): Out of memory on a 8723792-byte allocation.
I/dalvikvm(27130): "AsyncTask #1" prio=5 tid=11 RUNNABLE
I/dalvikvm(27130):   | group="main" sCount=0 dsCount=0 obj=0x42036a18 self=0x51c2eb08
I/dalvikvm(27130):   | sysTid=27151 nice=10 sched=0/0 cgrp=apps/bg_non_interactive handle=1371731208
I/dalvikvm(27130):   | schedstat=( 0 0 0 ) utm=197 stm=17 core=1
I/dalvikvm(27130):   at java.lang.AbstractStringBuilder.setLength(AbstractStringBuilder.java:~567)
I/dalvikvm(27130):   at java.lang.StringBuilder.setLength(StringBuilder.java:44)

You could try to use jvisualvm, the tool that comes with the jdk to profile the execution? Maybe there is something you are not taking into account, because for me is very odd to have a OutOfMemory with just a few MB. — Pablo Lozano, Mar 28 '14 at 08:20

score 0 · Answer 1 · answered Mar 26 '14 at 09:57

0

Setting length to 0 doesn't automatically invoke the GC to kick in. What you can do is have a loop and call System.gc, then wait for a while until available memory increases. Then break from the loop and continue with your next process.

You can also try allocating a new builder rather than clearing the buffer in each iteration.

answered Mar 26 '14 at 09:57

Sajal Dutta

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As an addition, there is a small discussion given [here](http://stackoverflow.com/a/5193094/1798304) about that issue. – MalaKa Mar 26 '14 at 10:02
@MalaKa This question looks the same as the question link you provided. – Sajal Dutta Mar 26 '14 at 10:04
Yes, that's why I provided a link to one of the answers with a discussion in the comments that might be interesting (and supporting your answer). What's the issue? – MalaKa Mar 26 '14 at 10:10
@MalaKa Was thinking if this should be marked as duplicate. – Sajal Dutta Mar 26 '14 at 10:11
Okay, I see. But I don't think so, since this is question is about a particular problem and the other question is more best practice. Similar, but to me not duplicate. – MalaKa Mar 26 '14 at 10:16
Yes I have read that link before. Problem is allocating new builder is not fast enough for the garbage collector. So once new builder is created again with 8Mb I got OutOfMemoryError. – Ivan Mar 26 '14 at 12:10
@Ivan Did you try what I suggested? – Sajal Dutta Mar 26 '14 at 13:01
I am not free to do so yet, but thanks for the suggestion. Will try later. For the moment I will just wrap up the whole thing to catch the OOME and return the unprocessed string. – Ivan Mar 26 '14 at 13:23
Hmm... not really working. Whenever it calls setLength(0), it kicks in to allocate a 8Mb slot and OOME, no matter where I put System.gc before or after setlength(0)... I tried waiting for 1000ms after calling System.gc – Ivan Mar 27 '14 at 15:17
@Ivan First do setLength to 0. Then call gc. After that wait 1 second. See if there was any change on available free space. If there was, do the allocation. – Sajal Dutta Mar 27 '14 at 16:34
That is what I did. Before gc kick in I got OOEM at setlength(0) – Ivan Mar 27 '14 at 18:26
@Ivan From the code you posted, I do not see anything special going on. Before you even do the first allocation, can you please check how much available memory you have? I think by the time you start allocating for the buffer, you are already short in memory. – Sajal Dutta Mar 28 '14 at 08:51

Strange OutOfMemoryError at StringBuilder setLength(0)

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