Possible deadlock in ExpressionCacheImpl (on _lock instance)
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Key: TAPESTRY-2382
URL: https://issues.apache.org/jira/browse/TAPESTRY-2382
Project: Tapestry
Issue Type: Bug
Components: Framework
Affects Versions: 4.1.3
Reporter: Alexander Gavrilov
Priority: Critical
Fix For: 4.1.6
Under some circumstances deadlock occurs in the ExpressionCacheImpl.
1)Thread Ta opening a Page Pa. Page Pa does not bound to the current request
cycle, so new Instance requested from PageSource and current thread enter to
the synchronized _pool.borrowObject(key)
2) At this time thread Tb render page Pb, and for some property evaluates
expression binding. So ExpressionCacheImpl's _lock locked by thread Tb. Result
of expression evaluation is a reference to the Page Pc instance, which is not
bound to the current thread, so new Instance requested from PageSource and
current thread tried to enter to the synchronized _pool.borrowObject(key)
which is locked by Ta.
3) Thread Ta worked creating new Page Pa Instance, which is not exists in the
pool, so a new Page instance should be created. In the proccess of parsing page
loader try to evaluate expression binding and try to lock a
ExpressionCacheImpl's _lock, which is locked by thread Tb.
4) Whe have a deadlock, so no new page instance and expression could be created
and evaluated.
This causes a serios problems while system startup, so we need to restart our
app many times, untill it warmed up.
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