On 8 Apr 2014, at 19:12, Pavel Rappo <pavel.ra...@oracle.com> wrote:
> Hi Sean, Sherman
>
> as far as the client is using ZipFileInputStream in a multithreaded fashion
> (de facto), don't we have to rethink synchronization for the machinery of
> ZipFileInputStream.read? As far as I understand it's not enough to put this
> particular read of 'rem' into the synchronized block, as there are
> at least 2 more accesses to it (and only in the 'read' method). We're reading
> it in the synchronized block, fine, but all the corresponding reads/writes
> have to be done with respect to 'happens-before' relationship between them.
Agreed. There doesn’t appear, or at least I cannot find, any statement in
ZipFile about its thread-safety ( or lack there of ), but the implementation of
ZipFile appears to be “somewhat” thread-safe. The InputStreams returned by
getInputStream(ZipEntry) are not. Sean’s testcase clearly shows that a single
InputStream is being shared across multiple threads. Unless we want to make
these streams thread-safe then we probably should not make any changes here.
-Chris.
>
> -Pavel
>
> On 8 Apr 2014, at 18:29, Seán Coffey <sean.cof...@oracle.com> wrote:
>
>> Sherman,
>>
>> I see rem == 0 condition becoming true before the zentry variable is set to
>> 0 (in close()) - in a multi threaded scenario like this one, we could have
>> zero remaining bytes in zentry and yet have a zentry != 0 - your suggestion
>> would prevent the SEGV (since we're in the sync block) but we would
>> needlessly cycle into the ensureOpenOrZipException() and ZipFile.read code
>> (line 713) if another thread tasked with the close() call was knocked off by
>> the dispatcher during the various rem == 0 checks that we make : e.g
>>
>> 722 if (rem == 0) {
>> 723 close();
>> 724 }
>>
>> Am I reading this correctly ?
>>
>> regards,
>> Sean.
>>
>> On 08/04/2014 16:59, Xueming Shen wrote:
>>> Hi Sean,
>>>
>>> It might be more explicit to check "if (zentry == 0)" here?
>>>
>>> -Sherman
>>>
>>> On 4/8/14 8:21 AM, Seán Coffey wrote:
>>>> A recently reported bug shows a race condition is possible on the rem == 0
>>>> check in ZipFile.read(byte b[], int off, int len). A bad check can result
>>>> in referencing a jzentry structure that might already be freed and hence
>>>> result in a SEGV. The fix is trivial and involves moving the rem == 0
>>>> check into a synchronized block. The ZipFile API itself is not thread safe
>>>> so having mutiple threads operate on the same ZipFileInputStream is
>>>> something that should never be performed.
>>>>
>>>> webrev : http://cr.openjdk.java.net/~coffeys/webrev.8038491/webrev/
>>>>
>>>> regards,
>>>> Sean.
>>>
>>
>
