Details
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Task
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Status: Open
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Major
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Resolution: Unresolved
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10.3.1.4
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None
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Normal
Description
Synchronization with respect to Clobs is a bit tricky.
A full review of synchronization should be performed, and documentation and actual behavior must be made in agreement with each other.
The synchronization wrt. Clob is made tricker due to the many streams that can be used to read or write its value.
The main classes to review will be (there might be more):
a) EmbedClob
b) StoreStreamClob
c) ClobStreamControl (may be renamed to TemporaryClob)
d) ClobUtf8Writer
e) ClobAsciiStream
f) ClobUpdateableReader
We should also clarify and document what is supposed to be allowed. Can
you read from one stream and write to another one at the same time, both
from the same Clob?
Can you expect the ascii stream and the character stream to be in sync
if you read from both of them?
A related issue is that of garbage collection of underlying resources
before the streams are closed. DERBY-2734 has already been filed for
this.
I would like to try a little experiment by using a few simple
annotations to document intended synchronization policies. These are the
annotations defined in the book "Java Concurrency in Practice" by Brian
Goetz et al, and the JavaDoc for them can be found here:
http://javaconcurrencyinpractice.com/annotations/doc/index.html
Since we are still using Java 1.4, the annotations must be used as
comments. I still think they are valuable, as we do not use any tools to
document/check synchronization anyway.
Briefly, the following four annotations are defined:
@GuardedBy
@Immutable
@NotThreadSafe
@ThreadSafe
Attachments
Issue Links
- is part of
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DERBY-2646 Cleanup of Clob control/support structures
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- Closed
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- relates to
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DERBY-4129 jvm level Deadlock between 2 threads accessing the same connection
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- Open
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