On 8 Apr 2014, at 19:41, Xueming Shen <xueming.s...@oracle.com> wrote:
> On 4/8/14 11:33 AM, Chris Hegarty wrote:
>> 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.
>>
>
> It is a reasonable use scenario to close a java.io.InputStream via a
> different thread and it
> definitely should not lead to a SEGV. But java.io.InputStream itself is not
> "thread-safe". To
> read from a java.io.InputStream via multiple thread is kinda of useless use
> scenario, which
> normally means unpredictable reading result for those read operation.
Ok, sounds reasonable.
-Chris.
>
> -Sherman
>
>>
>>> -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.
>
