[8] RFR of 8066985: Java Webstart downloading packed files can result in Timezone set to UTC
mikhail cherkasov
mikhail.cherkasov at oracle.com
Tue Mar 24 20:14:54 UTC 2015
Hi there,
There's a new webrev:
http://cr.openjdk.java.net/~mcherkas/8066985/webrev.02/
I reduced the a thread number in the test, because with big count of
threads I got OOM on JPRT.
And extract common part form PackerImpl and UnpackerImpl to Utils.
Thanks,
Mikhail.
On 3/20/2015 6:04 PM, mikhail cherkasov wrote:
>
> On 3/19/2015 7:29 PM, Peter Levart wrote:
>> On 03/19/2015 04:46 PM, Peter Levart wrote:
>>> On 03/19/2015 02:53 PM, Kumar Srinivasan wrote:
>>>> Mikhail,
>>>>
>>>> You can move the common utilitieschangeDefaultTimeZoneToUtc and
>>>> restoreDefaultTimeZoneto Utils.java.
>>>>
>>>> Also I am not sure how effective the test is ? does it catch the
>>>> issue ?
>>>> if you don't have the fix in PackerImpl and UnpackerImpl ?
>>>>
>>>> Otherwise it looks good, and I can sponsor this patch for you.
>>>>
>>>> Kumar
>>>
>>> Hi Mikhail,
>>>
>>> Is this code part of some utility so that it is executed exclusively
>>> in it's own JVM, or can it also be executed by some public API or
>>> internal JVM thread? It appears to be the later (used by
>>> java.util.jar.Pack200 public API), but haven't checked.
>>>
>>> In case of the later, I think it is very strange that the code
>>> changes global JVM timezone, albeit just temporarily. This could
>>> affect other code that needs default TZ and executes concurrently.
>>>
>>> Even in case of the former, if the PackerImpl.pack can be executed
>>> by multiple concurrent threads and if UnpackerImpl.unpack can be
>>> executed by multiple concurrent threads, what guarantees that some
>>> PackerImpl.pack thread is not executed concurrently with some
>>> UnpackerImpl.unpack thread? You only track each method separately.
> Agree, I'll move changeDefaultTimeZoneToUtc and restoreDefaultTimeZone
> to Util class, so TZ changes will be managed in one place for both
> PackerImpl and UnpackerImpl classes.
>
> NonPack200 threads that reads/writes DTZ can collide with Pack200, but
> there's other bug that should fix this:
> https://bugs.openjdk.java.net/browse/JDK-8073187
>
> My fix is only for jdk8 and 7, and it focused on making
> packer/unpacker safe for concurrent use, because now applets and JNLP
> uses packer/unpacker concurrently and this can
> lead to DTZ changing to UTC.
>
>>>
>>>
>>> Regards, Peter
>>
>> I guess this default TZ manipulation is needed because
>> JarOutputStream/JarInputStream don't provide constructors that would
>> take a TZ object, but always use default TZ, right?
>>
>> The cleanest way would be to add such constructors, but if this is
>> too much for 8u, then perhaps some internal ThreadLocal<TZ> could be
>> exposed to both PackerImpl/UnpackerImpl and Jar[Zip]Input[Output]
>> stream internals. It think the use of default TZ in Jar/Zip/Streams
>> is very localized. It is needed to convert local time (specified as
>> DOS time) to and from epoch-based time exposed in ZipEntry. The code
>> is located in package-private class java.util.zip.ZipUtils in methods
>> dosToJavaTime /javaToDosTime (or equivalent extendedDosToJavaTime /
>> javaToExtendedDosTime in JDK9).
> all solutions that you described require introducing a new API and
> this can not be done for jdk7 and 8, so that's why JDK-8073187 was
> created.
> The main purpose of this fix is to make packed jars delivery save for
> applets/jnlp application.
>
>>
>> Another way would be to provide a general thread-local default TZ
>> override in TimeZone itself. Something like the following:
>>
>> ===================================================================
>> --- jdk/src/share/classes/java/util/TimeZone.java
>> +++ jdk/src/share/classes/java/util/TimeZone.java
>> @@ -630,8 +630,11 @@
>> * method doesn't create a clone.
>> */
>> static TimeZone getDefaultRef() {
>> - TimeZone defaultZone = defaultTimeZone;
>> + TimeZone defaultZone = threadLocalTimeZone.get();
>> if (defaultZone == null) {
>> + defaultZone = defaultTimeZone;
>> + }
>> + if (defaultZone == null) {
>> // Need to initialize the default time zone.
>> defaultZone = setDefaultZone();
>> assert defaultZone != null;
>> @@ -713,6 +716,20 @@
>> defaultTimeZone = zone;
>> }
>>
>> + public void withThreadDefaultDo(Runnable runnable) {
>> + TimeZone prevZone = threadLocalTimeZone.get();
>> + threadLocalTimeZone.set(this);
>> + try {
>> + runnable.run();
>> + } finally {
>> + if (prevZone == null) {
>> + threadLocalTimeZone.remove();
>> + } else {
>> + threadLocalTimeZone.set(prevZone);
>> + }
>> + }
>> + }
>> +
>> /**
>> * Returns true if this zone has the same rule and offset as
>> another zone.
>> * That is, if this zone differs only in ID, if at all. Returns
>> false
>> @@ -760,6 +777,8 @@
>> */
>> private String ID;
>> private static volatile TimeZone defaultTimeZone;
>> + private static final ThreadLocal<TimeZone> threadLocalTimeZone =
>> + new ThreadLocal<>();
>>
>> static final String GMT_ID = "GMT";
>> private static final int GMT_ID_LENGTH = 3;
>>
>>
>> Regards, Peter
>>
>>>
>>>>
>>>>
>>>> On 3/18/2015 3:07 PM, Kumar Srinivasan wrote:
>>>>>
>>>>> Hello Mikhail,
>>>>>
>>>>>> Hi all,
>>>>>>
>>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8066985
>>>>>>
>>>>>> The problem is that packer/unpacker changes global state( default
>>>>>> time zone ) without proper synchronization:
>>>>>> http://hg.openjdk.java.net/jdk9/client/jdk/file/a159e5358e25/src/java.base/share/classes/com/sun/java/util/jar/pack/PackerImpl.java#l85
>>>>>>
>>>>>>
>>>>>> however javadoc says that it's save to use it in concurrent way
>>>>>> if each thread has it's own packer/unpacker instance:
>>>>>> http://hg.openjdk.java.net/jdk9/client/jdk/file/a159e5358e25/src/java.base/share/classes/java/util/jar/Pack200.java#l149
>>>>>>
>>>>>>
>>>>>> The fix is:
>>>>>> 1. first packer/unpacker saves default time zone
>>>>>> 2. the last set it back.
>>>>>>
>>>>>> Webrev:
>>>>>> http://cr.openjdk.java.net/~mcherkas/8066985/webrev.00/
>>>>>
>>>>> The above link is wrong!, it takes me to webrev for 8073187,
>>>>> which has only the PackerImpl changes.
>>>>>
>>>>> I am guessing the link should be:
>>>>> http://cr.openjdk.java.net/~mcherkas/8066985/webrev.00/
>>>>>
>>>>> Kumar
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Mikhail.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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