[pull] master from bitcoin:master#1675
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The cs_LastBlockFile mutex is redundant: all critical sections are already covered by cs_main. This is demonstrated in this patch by replacing all instances of locking cs_LastBlockFile with pairs of `AssertLockHeld(::cs_main)` and `EXCLUSIVE_LOCKS_REQUIRED(::cs_main)` annotations. No additional `::cs_main` LOCK(...)s are introduced. It is also not clear for which sections `cs_LastBlockFile` is responsible for. It is annotated for `m_blockfile_cursors`, but sporadically and inconsistently also covers `m_blockfile_info`. Since it has no semantic meaning, and seems confusing to developers, remove it.
ec6cf49 blockstorage: Remove cs_LastBlockFile recursive mutex (sedited) Pull request description: The `cs_LastBlockFile` mutex is redundant: all critical sections are already covered by cs_main. This is demonstrated in this patch by replacing all instances of locking `cs_LastBlockFile` with pairs of `AssertLockHeld(::cs_main)` and `EXCLUSIVE_LOCKS_REQUIRED(::cs_main)` annotations. No additional `::cs_main` LOCK(...)s are introduced (besides for test-only code). It is also not clear for which sections `cs_LastBlockFile` is responsible for. It is annotated for `m_blockfile_cursors`, but sporadically and inconsistently also covers `m_blockfile_info` (e.g. in `LoadBlockIndexDB`). Since it has no semantic meaning, and seems confusing to developers, remove it. An alternative to this patch would be expanding the scope of what `cs_LastBlockFile` covers and turning it into a non-recursive mutex. I prepared such a patch some time ago, but found it unsatisfactory. It was not clear to me if the lock was now covering too much or too little, and its purpose remained unclear. If this patch is accepted, I would expect the project to eventually implement a separate, narrowly-scoped block storage lock to allow for a more parallelizable block processing routine. ACKs for top commit: stickies-v: re-ACK ec6cf49 janb84: re- ACK ec6cf49 pablomartin4btc: ACK ec6cf49 Tree-SHA512: e5942bc87300b0db9a0b91d5fe26dab455049e6cef7c96bb12b28141fa04711d46c6af105c0e1a83a9f261edde2c8b8b43ecf577a27d54b4610d784676a85627
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