RFR 8170541: serviceability/jdwp/AllModulesCommandTest.java fails intermittently on Windows and Solaris

Mon Feb 26 19:51:45 UTC 2018

Hi David and Sergei,

On 2/20/18 10:16 PM, serguei.spitsyn at oracle.com wrote:
> Hi David,
>
>
> On 2/20/18 20:02, David Holmes wrote:
>> Hi Daniil,
>>
>> Good find on this!
>>
>> What does the actual spec say about the length of things and how they 
>> may be split across multiple packets? Are we guaranteed that at most 
>> two packets will be involved?

The JDWP spec 
(https://docs.oracle.com/javase/9/docs/specs/jdwp/jdwp-spec.html) says 
nothing about splitting JDWP reply packets at all but the implementation 
limits the max number of the sent packets to two packets max. The 
implementation is dated back to the initial load that happened in 2007 
and the information about the related Jira issue is missing.

open/src/jdk.jdwp.agent/share/native/libdt_socket/socketTransport.c

836    data = packet->type.cmd.data;
837    /* Do one send for short packets, two for longer ones */
838    if (data_len <= MAX_DATA_SIZE) {
839        memcpy(header + JDWP_HEADER_SIZE, data, data_len);
840        if (send_fully(socketFD, (char *)&header, JDWP_HEADER_SIZE + 
data_len) !=
841            JDWP_HEADER_SIZE + data_len) {
842            RETURN_IO_ERROR("send failed");
843        }
844    } else {
845        memcpy(header + JDWP_HEADER_SIZE, data, MAX_DATA_SIZE);
846        if (send_fully(socketFD, (char *)&header, JDWP_HEADER_SIZE + 
MAX_DATA_SIZE) !=
847            JDWP_HEADER_SIZE + MAX_DATA_SIZE) {
848            RETURN_IO_ERROR("send failed");
849        }
850        /* Send the remaining data bytes right out of the data area. */
851        if (send_fully(socketFD, (char *)data + MAX_DATA_SIZE,
852                       data_len - MAX_DATA_SIZE) != data_len - 
MAX_DATA_SIZE) {
853            RETURN_IO_ERROR("send failed");
854        }
855    }

>> What about for other things eg:
>>
>>  68     protected byte[] readJdwpString(DataInputStream ds) throws 
>> IOException {
>>   69         byte[] str = null;
>>   70         int len = ds.readInt();
>>   71         if (len > 0) {
>>   72             str = new byte[len];
>>   73             ds.read(str, 0, len);
>>   74         }
>>
>> might we get a short-read of the string if it is split across 
>> multiple packets?
>
This and all other reads happen not directly from the socket input 
stream but rather from the  DataInputStream object that is constructed 
in  JdwpReply.initFromStream(InputStream) method. With the proposed fix 
we do ensure that the created DataInputStream object contains data from 
both packets in cases when the reply was split in two packets.

> Nice catch!
> Even though this fix is enough to resolve this problem now, there is a 
> chance,
> it can fail in the future when more modules are added to the platform.
>
>
>> I'm wondering if all these reads should be loops, ensuring we read 
>> the expected amount of data.
>>
Since the implementation of the socket transport limits the max number 
of packets the reply might be split in to two packets I don't think we 
really need it here.
>> One further comment - not sure why we need the print out for when we 
>> do read multiple packets?
>> That would seem to be a debugging aid.
>
> Yes, it helps to understand what happens.
> Many tests have a lack of tracing which makes it harder to debug and 
> understand failures.
That is correct.  This additional tracing was added to help to 
understand the possible failures in the future.
>
>
> Thanks,
> Serguei
>
>>
>> Thanks,
>> David
>>
Thanks,
Daniil

>> On 21/02/2018 10:14 AM, Daniil Titov wrote:
>>> Hi Serguei,
>>>
>>> A new version of the webrev that has these strings reformatted is at 
>>> http://cr.openjdk.java.net/~dtitov/8170541/webrev.02/
>>>
>>> Thank you!
>>>
>>> Best regards,
>>>
>>> Daniil
>>>
>>> *From: *"serguei.spitsyn at oracle.com" <serguei.spitsyn at oracle.com>
>>> *Date: *Tuesday, February 20, 2018 at 3:00 PM
>>> *To: *Daniil Titov <daniil.x.titov at oracle.com>, 
>>> "serviceability-dev at openjdk.java.net" 
>>> <serviceability-dev at openjdk.java.net>
>>> *Subject: *Re: RFR 8170541: 
>>> serviceability/jdwp/AllModulesCommandTest.java fails intermittently 
>>> on Windows and Solaris
>>>
>>> Hi Daniil,
>>>
>>> Interesting issue...
>>> Thank you for finding to the root cause so quickly!
>>>
>>> The fix looks good.
>>> Could I ask you to reformat these lines to make the L54 shorter ?:
>>>
>>>    54                 System.out.println("[" + getClass().getName() 
>>> + "] Only " + bytesRead + " bytes of " + dataLength +
>>>
>>>    55                         " were read in the first packet. 
>>> Reading the rest...");
>>>
>>> Thanks,
>>> Serguei
>>>
>>>
>>> On 2/20/18 09:24, Daniil Titov wrote:
>>>
>>>     Please review the changes that fix intermittent failure of
>>>     serviceability/jdwp/AllModulesCommandTest.java test.
>>>
>>>     The problem here is that for a large data the JDWP agent
>>>     (socketTransport_writePacket() method in
>>> src/jdk.jdwp.agent/share/native/libdt_socket/socketTransport.c )
>>>     sends 2 packets and in some cases only the first packet is received
>>>     at the time when the test reads the reply from the JDWP agent. 
>>> Since
>>>     the test does not check that all data is received in the first
>>>     packet the correlation between commands and replies became broken
>>>     (the unread second packet is read by the next command and the reply
>>>     for the next command is read by the next after next command and 
>>> so on).
>>>
>>>     Bug: https://bugs.openjdk.java.net/browse/JDK-8170541
>>>
>>>     Webrev: http://cr.openjdk.java.net/~dtitov/8170541/webrev.01
>>>
>>>     The tests ran successfully with Mach5.
>>>
>>>     Best regards,
>>>
>>>     Daniil
>>>
>>>
>>>
>