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Make FindBlockByHeight constant-time.

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Remove the pnext pointer in CBlockIndex, and replace it with a
vBlockIndexByHeight vector (no effect on memory usage). pnext can
now be replaced by vBlockIndexByHeight[nHeight+1], but
FindBlockByHeight becomes constant-time.

This also means the entire mapBlockIndex structure and the block
index entries in it become purely blocktree-related data, and
independent from the currently active chain, potentially allowing
them to be protected by separate mutexes in the future.
This commit is contained in:
Pieter Wuille
2013-05-12 15:50:22 +02:00
parent 5b5d399593
commit 0fe8010a10
5 changed files with 36 additions and 51 deletions
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24
src/main.h
View File

@@ -69,6 +69,7 @@ extern CScript COINBASE_FLAGS;
extern CCriticalSection cs_main;
extern std::map<uint256, CBlockIndex*> mapBlockIndex;
extern std::vector<CBlockIndex*> vBlockIndexByHeight;
extern std::set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexValid;
extern uint256 hashGenesisBlock;
extern CBlockIndex* pindexGenesisBlock;
@@ -1589,10 +1590,8 @@ enum BlockStatus {
/** The block chain is a tree shaped structure starting with the
* genesis block at the root, with each block potentially having multiple
* candidates to be the next block. pprev and pnext link a path through the
* main/longest chain. A blockindex may have multiple pprev pointing back
* to it, but pnext will only point forward to the longest branch, or will
* be null if the block is not part of the longest chain.
* candidates to be the next block. A blockindex may have multiple pprev pointing
* to it, but at most one of them can be part of the currently active branch.
*/
class CBlockIndex
{
@@ -1603,9 +1602,6 @@ public:
// pointer to the index of the predecessor of this block
CBlockIndex* pprev;
// (memory only) pointer to the index of the *active* successor of this block
CBlockIndex* pnext;
// height of the entry in the chain. The genesis block has height 0
int nHeight;
@@ -1643,7 +1639,6 @@ public:
{
phashBlock = NULL;
pprev = NULL;
pnext = NULL;
nHeight = 0;
nFile = 0;
nDataPos = 0;
@@ -1664,7 +1659,6 @@ public:
{
phashBlock = NULL;
pprev = NULL;
pnext = NULL;
nHeight = 0;
nFile = 0;
nDataPos = 0;
@@ -1733,7 +1727,11 @@ public:
bool IsInMainChain() const
{
return (pnext || this == pindexBest);
return nHeight < (int)vBlockIndexByHeight.size() && vBlockIndexByHeight[nHeight] == this;
}
CBlockIndex *GetNextInMainChain() const {
return nHeight+1 >= (int)vBlockIndexByHeight.size() ? NULL : vBlockIndexByHeight[nHeight+1];
}
bool CheckIndex() const
@@ -1762,9 +1760,9 @@ public:
const CBlockIndex* pindex = this;
for (int i = 0; i < nMedianTimeSpan/2; i++)
{
if (!pindex->pnext)
if (!pindex->GetNextInMainChain())
return GetBlockTime();
pindex = pindex->pnext;
pindex = pindex->GetNextInMainChain();
}
return pindex->GetMedianTimePast();
}
@@ -1779,7 +1777,7 @@ public:
std::string ToString() const
{
return strprintf("CBlockIndex(pprev=%p, pnext=%p, nHeight=%d, merkle=%s, hashBlock=%s)",
pprev, pnext, nHeight,
pprev, GetNextInMainChain(), nHeight,
hashMerkleRoot.ToString().c_str(),
GetBlockHash().ToString().c_str());
}