Add cursor to iterate over utxo set, use this in gettxoutsetinfo #7756

1. 
   laanwj commented at 4:48 pm on March 28, 2016: member

   I need this for something else, but I think this is simply a better API. I also vaguely remember this has been discussed before.

   • Add a method Cursor() to CCoinsView that returns a cursor which can be used to iterate over the whole UTXO set.
   • Implement GetUTXOStats in terms of this, remove GetStats() method on CCoinsView.
   • Change gettxoutsetinfo RPC to use new GetUTXOStats function.

   This is not yet enough to break the dependency of txdb.cpp/h on main (there’s CDiskTxPos to cope with, for example), but it is a step toward that (see #7815).

2. laanwj added the label UTXO Db and Indexes on Mar 28, 2016
3. laanwj added the label RPC on Mar 28, 2016
4. laanwj force-pushed on Mar 30, 2016
5. 
   laanwj commented at 9:12 am on March 31, 2016: member

   Travis fail is unrelated (https://github.com/bitcoin/bitcoin/issues/7470#issuecomment-202332354), respinning.
6. laanwj force-pushed on Apr 6, 2016
7. 
   laanwj commented at 11:05 am on April 6, 2016: member

   Rebased
8. in src/coins.cpp: in c1331def20 outdated

   44@@ -45,7 +45,7 @@ bool CCoinsView::GetCoins(const uint256 &txid, CCoins &coins) const { return fal
   45 bool CCoinsView::HaveCoins(const uint256 &txid) const { return false; }
   46 uint256 CCoinsView::GetBestBlock() const { return uint256(); }
   47 bool CCoinsView::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return false; }
   48-bool CCoinsView::GetStats(CCoinsStats &stats) const { return false; }
   49+CCoinsViewCursor *CCoinsView::Cursor() const { return 0; }
   

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   sipa commented at 11:10 am on April 6, 2016:

   Using NULL would be clearer as it’s a pointer.

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   laanwj commented at 12:05 pm on April 6, 2016:

   Bjarne Stroustrup taught me not to use NULL in c++ code: http://www.stroustrup.com/bs_faq2.html#null I don’t care deeply about this though.

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   sipa commented at 2:49 pm on April 6, 2016:

   Interesting. Comment retracted.
9. 
   sipa commented at 11:28 am on April 6, 2016: member

   • rpc: Add method gettxoutsetinfo2 that uses new Cursor method

   That seems outdated.

10. 
    laanwj commented at 12:02 pm on April 6, 2016: member

    That seems outdated.

    Yes, I’ve removed that in the rebase, I had multiple commits with two getutxosetinfo in an intermediate step but that was annoying to rebase over #7766.

11. laanwj force-pushed on Apr 6, 2016
12. in src/txdb.cpp: in eacf28cb38 outdated

    166+    return pcursor->Valid();
    167+}
    168+
    169+void CCoinsViewDBCursor::Next()
    170+{
    171+    while (true) {
    

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    sipa commented at 2:52 pm on April 6, 2016:

    This should never loop more than once, I think? Seems that the loop here could hide potential problems.

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    laanwj commented at 11:42 am on April 8, 2016:

    Right, there can’t be holes between DB_COINS records, will change this loop.
13. in src/txdb.cpp: in eacf28cb38 outdated

    176+            return;
    177     }
    178-    stats.hashSerialized = ss.GetHash();
    179-    stats.nTotalAmount = nTotalAmount;
    180-    return true;
    181+    keyTmp.first = 0; // Invalidate cached key after last record so that GetKey() returns false
    

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    sipa commented at 2:53 pm on April 6, 2016:

    Unreachable code?
14. 
    laanwj commented at 8:14 am on April 9, 2016: member

    Pushed a commit that should address @sipa’s comment: get rid of loop, no more chance of hiding failures.
15. laanwj force-pushed on Apr 9, 2016
16. 
    sipa commented at 5:59 pm on April 12, 2016: member

    utACK 299fad9
17. txdb: Add Cursor() method to CCoinsView to iterate over UTXO set

    Add a method Cursor() to CCoinsView that returns a cursor which can be
    used to iterate over the whole UTXO set.
    
    - rpc: Change gettxoutsetinfo to use new Cursor method
    
    - txdb: Remove GetStats method - Now that GetStats is implemented in
      terms of Cursor, remove it.

    509cb006d5
18. laanwj force-pushed on Apr 15, 2016
19. 
    laanwj commented at 2:33 pm on April 15, 2016: member

    Squashed eacf28c 299fad9 into 509cb00
20. laanwj merged this on Apr 15, 2016
21. laanwj closed this on Apr 15, 2016

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Contributors
laanwj sipa

Labels
UTXO Db and Indexes RPC/REST/ZMQ