prevector: fix 2 bugs in currently unreached code paths #7888
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Concept ACK. |
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Nice catch, thanks. Code review ACK, but agree that a test for this behaviour would be welcome. |
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Fixes a bug in which pop_back did not call the deleted item's destructor. Using the most general erase() implementation to implement all the others prevents similar bugs because the coupling between deallocation and destructor invocation only needs to be maintained in one place. Also reduces duplication of complex memmove logic.
- add a swap operation to prevector tests (fails due to broken prevector::swap) - fix 2 prevector test operation conditions that were impossible
swap was using an incorrect condition to determine when to apply an optimization (not swapping the full direct[] when swapping two indirect prevectors). Rather than correct the optimization I'm removing it for simplicity. Removing this optimization minutely improves performance in the typical (currently only) usage of member swap(), which is swapping with a freshly value-initialized object.
laanwj
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Fuzzbawls
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a8b965e Explicitly initialize prevector _union (random-zebra) bdd98e8 [Trivial] Add a comment on the use of prevector in script. (random-zebra) bbaa6e3 Clarify prevector::erase and avoid swap-to-clear (random-zebra) 28a8435 prevector: assert successful allocation (random-zebra) de41cb5 Only call clear on prevector if it isn't trivially destructible (random-zebra) 8784df3 Make CScript (and prevector) c++11 movable. (random-zebra) 83f9ac6 serialize: Deprecate `begin_ptr` / `end_ptr` (random-zebra) c3ecc12 prevector: add C++11-like data() method (random-zebra) 5490aa0 test prevector::swap (random-zebra) 035760e prevector::swap: fix (unreached) data corruption (random-zebra) 0e71400 prevector: destroy elements only via erase() (random-zebra) 9811a68 [Core] Prevector type (random-zebra) Pull request description: Based on: - [x] #1554 This introduces `prevector<N, T>`, a new basic data type which is a fully API compatible drop-in replacement for `std::vector<T>` and uses it for the script, to reduce the considerable memory overhead of vectors in cases where they normally contain a small number of small elements. Original tests in Bitcoin showed a reduction in dbcache memory usage by **23%**, and made an initial sync **13%** faster. Backported from the following upstream's PRs, with only additional edits in the 2nd layer scripts (`masternode-payments`, `masternode-budget`) and in the unit tests (to address the differences in `insecure_rand`): - bitcoin#6914 - bitcoin#7888 - bitcoin#8850 - bitcoin#9349 - bitcoin#9505 - bitcoin#9856 - bitcoin#10534 - bitcoin#11011 - bitcoin#14028 ~~NOTE: Updates to `memusage.h` needed as well, when #1531 is merged.~~ ACKs for top commit: furszy: Tested ACK a8b965e . Fuzzbawls: ACK a8b965e Tree-SHA512: 203b660dd8d9f98780be660dae0ac951766ba438836bd6f0ec921e7749c1a84143f3b920fe49f2cc399f4aa7e763098f78746d3b6ff845bcf913bb13de984bc1
This was referenced Feb 15, 2021
zkbot
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Feb 17, 2021
Fix prevector bugs. Backports: bitcoin/bitcoin#7888 bitcoin/bitcoin#8671 Commits below are listed in stack order. pick bitcoin/bitcoin@f71d4a3 pick bitcoin/bitcoin@a7af72a pick bitcoin/bitcoin@4ed41a2 pick bitcoin/bitcoin@1e2c29f
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It looks like maybe this swap method is from an earlier iteration of prevector that used the LSB of size as a "direct/indirect" tag. The bad path isn't ever hit because in all current instances of swapping two prevectors, one is newly value-initialized and thus has an even size (0).