From b38a099eb79efa9cf1fa4c9fce68a4d7e3d423b5 Mon Sep 17 00:00:00 2001
From: Henning Baldersheim <balder@yahoo-inc.com>
Date: Tue, 2 Jun 2020 18:02:20 +0000
Subject: As the source bit vector might change in a different thread, ensure
 that we sample size once to avoid incosistent read outs during copy.

---
 .../vespa/searchlib/common/allocatedbitvector.cpp  | 29 ++++++++++++++++------
 .../vespa/searchlib/common/allocatedbitvector.h    |  2 +-
 2 files changed, 23 insertions(+), 8 deletions(-)

(limited to 'searchlib')

diff --git a/searchlib/src/vespa/searchlib/common/allocatedbitvector.cpp b/searchlib/src/vespa/searchlib/common/allocatedbitvector.cpp
index 3add7d1a328..cf159bccaca 100644
--- a/searchlib/src/vespa/searchlib/common/allocatedbitvector.cpp
+++ b/searchlib/src/vespa/searchlib/common/allocatedbitvector.cpp
@@ -17,6 +17,21 @@ size_t computeCapacity(size_t capacity, size_t allocatedBytes) {
     return possibleCapacity;
 }
 
+// This is to ensure that we only read size and capacity once during copy
+// to ensure that they do not change unexpectedly under our feet due to resizing in different thread.
+std::pair<BitVector::Index, BitVector::Index>
+extract_size_size(const BitVector & bv) {
+    BitVector::Index size = bv.size();
+    return std::pair<BitVector::Index, BitVector::Index>(size, size);
+}
+
+std::pair<BitVector::Index, BitVector::Index>
+extract_size_capacity(const AllocatedBitVector & bv) {
+    BitVector::Index size = bv.size();
+    BitVector::Index capacity = bv.capacity();
+    return std::pair<BitVector::Index, BitVector::Index>(size, capacity);
+}
+
 }
 
 AllocatedBitVector::AllocatedBitVector(Index numberOfElements) :
@@ -56,21 +71,21 @@ AllocatedBitVector::AllocatedBitVector(Index numberOfElements, Index capacityBit
 }
 
 AllocatedBitVector::AllocatedBitVector(const AllocatedBitVector & rhs) :
-    AllocatedBitVector(rhs, rhs.capacity())
+    AllocatedBitVector(rhs, extract_size_capacity(rhs))
 { }
 
 AllocatedBitVector::AllocatedBitVector(const BitVector & rhs) :
-    AllocatedBitVector(rhs, rhs.size())
+    AllocatedBitVector(rhs, extract_size_size(rhs))
 { }
 
-AllocatedBitVector::AllocatedBitVector(const BitVector & rhs, Index capacity_) :
+AllocatedBitVector::AllocatedBitVector(const BitVector & rhs, std::pair<Index, Index> size_capacity) :
     BitVector(),
-    _capacityBits(capacity_),
-    _alloc(allocatePaddedAndAligned(0, rhs.size(), capacity_))
+    _capacityBits(size_capacity.second),
+    _alloc(allocatePaddedAndAligned(0, size_capacity.first, size_capacity.second))
 {
     _capacityBits = computeCapacity(_capacityBits, _alloc.size());
-    memcpy(_alloc.get(),  rhs.getStart(), rhs.sizeBytes());
-    init(_alloc.get(), 0, rhs.size());
+    memcpy(_alloc.get(),  rhs.getStart(), numBytes(size_capacity.first - rhs.getStartIndex()));
+    init(_alloc.get(), 0, size_capacity.first);
     setBit(size());
     updateCount();
 }
diff --git a/searchlib/src/vespa/searchlib/common/allocatedbitvector.h b/searchlib/src/vespa/searchlib/common/allocatedbitvector.h
index c52c52354a1..5a7d2e634ea 100644
--- a/searchlib/src/vespa/searchlib/common/allocatedbitvector.h
+++ b/searchlib/src/vespa/searchlib/common/allocatedbitvector.h
@@ -73,7 +73,7 @@ private:
         BitVector::swap(rhs);
     }
 
-    AllocatedBitVector(const BitVector &other, Index capacity);
+    AllocatedBitVector(const BitVector &other, std::pair<Index, Index> size_capacity);
 
     /**
      * Prepare for potential reuse where new value might be filled in by
-- 
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