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https://issues.apache.org/jira/browse/TS-3744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14637643#comment-14637643
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Alan M. Carroll edited comment on TS-3744 at 7/22/15 9:17 PM:
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-The transform continuation will need to track the write ready state of the
cache VIO. In item (3) the continuation should mark that the cache VIO is in a
write ready state-. When you get to step 4.1 you would send a READ_READY to the
cache continuation using the same mechanism you send WRITE_READY to your
upstream. That is, you send WRITE_READY upstream when you can receive data and
send READ_READY downstream when you make data available to be read.
Keeping all the data in memory being a problem depends on how fast the slower
of your user agent and cache agent consume the data. This can be an issue in
the real world and the flow control logic was added to ameloriate the problem
by limiting the amount of buffer space consumed by a transaction.
was (Author: amc):
The transform continuation will need to track the write ready state of the
cache VIO. In item (3) the continuation should mark that the cache VIO is in a
write ready state. When you get to step 4.1 you would send a READ_READY to the
cache continuation using the same mechanism you send WRITE_READY to your
upstream. That is, you send WRITE_READY upstream when you can receive data and
send READ_READY downstream when you make data available to be read.
Keeping all the data in memory being a problem depends on how fast the slower
of your user agent and cache agent consume the data. This can be an issue in
the real world and the flow control logic was added to ameloriate the problem
by limiting the amount of buffer space consumed by a transaction.
> Crash (Seg Fault) when reenabling a VIO from a continuator which is different
> from the VIO's continuator.
> ---------------------------------------------------------------------------------------------------------
>
> Key: TS-3744
> URL: https://issues.apache.org/jira/browse/TS-3744
> Project: Traffic Server
> Issue Type: Bug
> Components: Plugins, TS API
> Affects Versions: 5.3.0
> Reporter: Pavel Vazharov
> Assignee: Alan M. Carroll
> Fix For: 6.1.0
>
>
> Hi,
> I'm trying to create ATS plugin which uses the API for cache write
> (TSCacheWrite, TSVConnWrite). For the write part, from a transformation, I'm
> trying to stream the data to both the client and the cache in the same time.
> The problem described below IMO can be summarized as - crash reenabling of
> one VIO from a continuator which is different from the VIO's continuator.
> Here is the backtrace of the crash.
> traffic_server: Segmentation fault (Address not mapped to object [0x28])
> traffic_server - STACK TRACE:
> /usr/local/bin/traffic_server(_Z19crash_logger_invokeiP9siginfo_tPv+0x8e)[0x4ad13e]
> /lib/x86_64-linux-gnu/libpthread.so.0(+0x10340)[0x2b9092c2a340]
> /usr/local/bin/traffic_server(_ZN7CacheVC8reenableEP3VIO+0x28)[0x6db868]
> /home/freak82/ats/src/plugins/ccontent/ccontent.so(+0x29e5)[0x2b9096bce9e5]
> /home/freak82/ats/src/plugins/ccontent/ccontent.so(+0x3094)[0x2b9096bcf094]
> /usr/local/bin/traffic_server(_ZN7EThread13process_eventEP5Eventi+0x120)[0x767ea0]
> /usr/local/bin/traffic_server(_ZN7EThread7executeEv+0x81b)[0x768aab]
> /usr/local/bin/traffic_server(main+0xee6)[0x495436]
> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5)[0x2b909387dec5]
> /usr/local/bin/traffic_server[0x49ba6f]
> It's like the VIO mutex->thread_holding or the VIO object itself are in some
> inappropriate state or invalid. The VIO has the same memory address as the
> originally created one and it's continuator is not explicitly destroyed
> (TSContDestroy). The associated buffer and reader are also alive.
> I'm not sure if the thing (writing "in-parallel") that I'm trying to do is
> possible with the current API, by design? Is it possible/allowed by design to
> copy bytes to one VIO buffer and reenable the same VIO from another
> continuator, not the same continuator as the one of the VIO.
> If it's possible am I doing something wrong or this is a bug?
> Basically, I'm trying to do it in the following way. The explanations skip
> the error handling.
> 1. On transformation start, on the first EVENT_IMMEDIATE from the upstream,
> the code initializes the client stream (TSBuffer, TSBufferReader and TSVIO as
> in the null-transform plugin) and then start the cache write (TSCacheWrite)
> with a created and digested cache key (TSCacheKey).
> 2. On EVENT_CACHE_OPEN_WRITE, the code initializes the cache stream
> (TSBuffer, TSBufferReader and TSVIO) in the same way as the client stream,
> but using the passed TSCont and TSVConn from the event data. So far, it works
> as expected.
> 3. Both continuator callbacks, for the transformation and for the cache
> write, are handling events WRITE_READY and WRITE_COMPLETE. The transformation
> callback also handles EVENT_IMMEDIATE to know when there is more data from
> the upstream.
> I was thinking to mark every stream as ready when the corresponding callback
> receives WRITE_READY, and when both streams are ready to copy the available
> data from the upstream to them, then reenable the both streams and the
> upstream. Then when there are new data available from the upstream, to copy
> them again when the both streams becomes ready, etc, etc.
> Usually the first writes/copies and reenables are made from inside the
> TSCacheWrite, because it's reentrant and generates WRITE_READY for the cache
> continuator. These operations succeeds. The problem is that the plugin leads
> to crash in the ATS when it tries to reeenable the cache VIO from inside the
> transform continuator.
> I tried to pass whole data from the upstream to the client first, copying
> (TSIOBufferCopy) "in-paralles" them to a temporary buffer, and initiate cache
> write at the end of the transformation and then write the data from the
> buffer to the cache VIO (similarly to the metalink plugin). This also works
> as expected.
> Thanks,
> Pavel.
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