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[v6.24] Cling: prevent double release of Transactions #153

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[v6.24] Cling: prevent double release of Transactions #153

wants to merge 8 commits into from

Commits on Mar 31, 2021

  1. [cling] Fix alignment of Transaction allocation: 

    new of a char array might not have the correct alignment to hold a Transaction.
Allocate a Transaction itself directly, instead of in-place constructing it in
the character array.

Each Transaction in the pool is thus constructed through `new Transaction(S)`
and destructed through `delete T`, which is nicely symmetrical. The use of
`::operator new` and `::operator delete` isn't actually necessary.

While I'm at it, improve the assert message's wording.
    @Axel-Naumann
    Axel-Naumann committed Mar 31, 2021
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  2. [cling] Move PushTransactionRAII out of Interpreter: 

    This will allow Transaction remembering its RAII to not depend on Interpreter.
    @Axel-Naumann
    Axel-Naumann committed Mar 31, 2021
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  3. [cling] Order includes alphabetically (NFC).

    @Axel-Naumann
    Axel-Naumann committed Mar 31, 2021
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  4. [cling] Transaction needs to know its RAII: 

    This will allow the Intrepreter to prevent unload() on
Transactions held by RAIIs.
    @Axel-Naumann
    Axel-Naumann committed Mar 31, 2021
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  5. [cling] Assert that no nested attaches to unloading Transaction.

    @Axel-Naumann
    Axel-Naumann committed Mar 31, 2021
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  6. [cling] Prevent double delete / double TransactionPool-ing: 

    When a Transaction is unloaded for which *also* a ScopedTransactionRAII
is waiting, the latter will potentially access a deleted Transaction.
It can be deleted due to the Pool being full. Even if it is not deleted
(as is the case in root-project#7657 )
it will get pushed into the Pool once by unload() and a second time by
the RAII!

The two options to track this case were full-blown ref counting or noting
that a Transaction is attached to an RAII scope. If that is the case,
freeing the Transaction must be skipped, as the RAII will take care of it.
    @Axel-Naumann
    Axel-Naumann committed Mar 31, 2021
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  7. [cling] Remove historical leftover in TransactionPool size (NFC).

    @Axel-Naumann
    Axel-Naumann committed Mar 31, 2021
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  8. [cling] Assert released transaction is != last in pool: 

    a cheap way to notice what went wrong in root-project#7657.
    @Axel-Naumann
    Axel-Naumann committed Mar 31, 2021
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