* Fixed deadlock in class initialization. (#10540)
* Thread T1 may initialize HttpTester.Message that extends MutableHttpFields, so grabs the lock for the initialization of class MutableHttpFields.
* Thread T2 may initialize HttpFields, so grabs the lock for HttpFields and initializes field EMPTY, which calls new MutableHttpFields.
* To initialize MutableHttpFields, T1 must initialize HttpFields, but sees that its lock is taken and waits.
* To initialize HttpFields, T2 must create an instance and therefore initialize MutableHttpFields, but sees that its lock is taken and waits.
* Deadlock.
The solution is to use another class, EmptyHttpFields, to initialize HttpFields.EMPTY, so that there is no deadlock.
Signed-off-by: Joakim Erdfelt <joakim.erdfelt@gmail.com>
Co-authored-by: Simone Bordet <simone.bordet@gmail.com>
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