Copy construction of CBlockIndex objects is a footgun because of the
wide use of equality-by-pointer comparison in the code base. There are
also potential lifetime confusions of using copied instances, since
there are recursive pointer references (e.g. pprev).
We can't just delete the copy constructors because they are used for
derived classes (CDiskBlockIndex), so we mark them protected.
Delete move constructors and declare the destructor to satisfy the
"rule of 5."
This introduces an insignificant performance penalty, as it means locator
construction needs to use the skiplist-based CBlockIndex::GetAncestor()
function instead of the lookup-based CChain, but avoids the need for
callers to have access to a relevant CChain object.
and mark the inherited CBlockIndex#GetBlockHash public interface member
as deleted, to disallow calling it in the derived CDiskBlockIndex class.
Here is a failing test on master demonstrating the inconsistent behavior of the
current design: calling the same inherited public interface functions on the
same CDiskBlockIndex object should yield identical behavior.
```diff
diff --git a/src/test/validation_chainstatemanager_tests.cpp b/src/test/validation_chainstatemanager_tests.cpp
index 6dc522b421..dac3840f32 100644
--- a/src/test/validation_chainstatemanager_tests.cpp
+++ b/src/test/validation_chainstatemanager_tests.cpp
@@ -240,6 +240,15 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
const CBlockIndex* tip = chainman.ActiveTip();
BOOST_CHECK_EQUAL(tip->nChainTx, au_data.nChainTx);
+ // CDiskBlockIndex "is a" CBlockIndex, as it publicly inherits from it.
+ // Test that calling the same inherited interface functions on the same
+ // object yields identical behavior.
+ CDiskBlockIndex index{tip};
+ CBlockIndex *pB = &index;
+ CDiskBlockIndex *pD = &index;
+ BOOST_CHECK_EQUAL(pB->GetBlockHash(), pD->GetBlockHash());
+ BOOST_CHECK_EQUAL(pB->ToString(), pD->ToString());
+
```
The GetBlockHash() test assertion only passes on master because the different
methods invoked by the current design happen to return the same result. If one
of the two is changed, it fails like the ToString() assertion does.
Redefining inherited non-virtual functions is well-documented as incorrect
design to avoid inconsistent behavior (see Scott Meyers, "Effective C++", Item
36). Class usage is confusing when the behavior depends on the pointer
definition instead of the object definition (static binding happening where
dynamic binding was expected). This can lead to unsuspected or hard-to-track
bugs.
Outside of critical hot spots, correctness usually comes before optimisation,
but the current design dates back to main.cpp and it may possibly have been
chosen to avoid the overhead of dynamic dispatch. This solution does the same:
the class sizes are unchanged and no vptr or vtbl is added.
There are better designs for doing this that use composition instead of
inheritance or that separate the public interface from the private
implementations. One example of the latter would be a non-virtual public
interface that calls private virtual implementation methods, i.e. the Template
pattern via the Non-Virtual Interface (NVI) idiom.
and remove a now-redundant assert preceding a GetBlockHash() caller.
This protects against UB here, and in case of failure (which would
indicate a consensus bug), the debug log will print
bitcoind: chain.h:265: uint256 CBlockIndex::GetBlockHash() const: Assertion `phashBlock != nullptr' failed.
Aborted
instead of
Segmentation fault
fa832103aa Avoid integer sanitizer warnings in chain.o (MarcoFalke)
Pull request description:
The two changes make the code more self-documenting and also allow to remove 5 file-wide suppressions for the module
ACKs for top commit:
PastaPastaPasta:
utACK fa832103aa
jonatack:
ACK fa832103aa
Tree-SHA512: d32a06099c56eed9f69130a3209f989872acc593f849528acd7746ee6caa96688cc32de37e8e59ad5d25dcb8912e341f1a43e50642dadeff6ca7624d0873ad10
ef72e9bd41 doc: nChainTx needs to become a 64-bit earlier due to SegWit (Sjors Provoost)
Pull request description:
As of block 597,379 txcount is 460,596,047 (see `chainparams.cpp`), while `uint32` can handle up to 4,294,967,296.
Pre segwit the [minimum transaction size](https://en.bitcoin.it/wiki/Maximum_transaction_rate) was 166 bytes, so the worst case number of transactions per block was ~6000. As the original source comment for `unsigned int nChainTx` says, that should last until the year 2030.
With SegWit the smallest possible transaction is 60 bytes (potentially increased to 65 with a future soft fork, see #15482), without a witness:
```
4 bytes version
1 byte input count
36 bytes outpoint
1 byte scriptSigLen (0x00)
0 bytes scriptSig
4 bytes sequence
1 byte output count
8 bytes value
1 byte scriptPubKeyLen
1 byte scriptPubKey (OP_TRUE)
4 bytes locktime
```
That puts the maximum number of transactions per block at 16,666 so we might have to deal with this as early as a block 827,450 in early 2024.
Given that it's a memory-only thing and we want to allow users many years to upgrade, I would suggest fixing this in v0.20 and back-porting it.
ACKs for top commit:
practicalswift:
re-ACK ef72e9bd41
jarolrod:
ACK ef72e9bd41
theStack:
ACK ef72e9bd41
Tree-SHA512: d8509ba7641796cd82af156354ff3a12ff7ec0f7b11215edff6696e95f8ca0e3596f719f3492ac3acb4b0884ac4e5bddc76f107b656bc2ed95a8ef1b2b5d4f71
Instead of (ab)using the existing BLOCK_VALID_* flags to mark CBlockIndex entries which
we haven't yet fully validated (but assume validity for use with UTXO snapshot
loading), introduce a status flag that specifically marks an assumed-valid state.
This state is then removed in RaiseValidity() when the block has actually been
validated.
This distinction will allow us to make the necessary changes to various parts of the
system to facilitate assumeutxo/background chainstate validation but without leaking
details like snapshot height, as we had done previously.
Changes that actually make use of this flag follow in future commits.
* Rename RewindBlockIndex -> NeedsRedownload (follow-up to commit
d831e711ca)
* Fix typos
* Inline comments about faking chain data to avoid duplicating them
As suggested in #14711, pass height to CChain::FindEarliestAtLeast to
simplify Chain interface by combining findFirstBlockWithTime and
findFirstBlockWithTimeAndHeight into one
Extend findearliestatleast_edge_test in consequence
chain.h does not actually depend on the methods defined in pow.h, just its
include of consensus/params.h, which is standalone and can be included instead.
Confirmed by inspection and successful build.
Using VARINT with signed types is dangerous because negative values will appear
to serialize correctly, but then deserialize as positive values mod 128.
This commit changes the VARINT macro to trigger an error by default if called
with an signed value, and updates broken uses of VARINT to pass a special flag
that lets them keep working with no change in behavior.
1. nStatus of CBlockIndex is consistent with the definition of Enum(BlockStatus)
2. The BlockHeader is consistent with the type of variable defined in CBlockHeader
