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-rw-r--r--src/cuckoocache.h457
-rw-r--r--src/init.cpp2
-rw-r--r--src/script/sigcache.cpp77
-rw-r--r--src/script/sigcache.h9
-rw-r--r--src/test/test_bitcoin.cpp2
5 files changed, 506 insertions, 41 deletions
diff --git a/src/cuckoocache.h b/src/cuckoocache.h
new file mode 100644
index 0000000000..efd6a820b5
--- /dev/null
+++ b/src/cuckoocache.h
@@ -0,0 +1,457 @@
+// Copyright (c) 2016 Jeremy Rubin
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef _BITCOIN_CUCKOOCACHE_H_
+#define _BITCOIN_CUCKOOCACHE_H_
+
+#include <array>
+#include <algorithm>
+#include <atomic>
+#include <cstring>
+#include <cmath>
+#include <memory>
+#include <vector>
+
+
+/** namespace CuckooCache provides high performance cache primitives
+ *
+ * Summary:
+ *
+ * 1) bit_packed_atomic_flags is bit-packed atomic flags for garbage collection
+ *
+ * 2) cache is a cache which is performant in memory usage and lookup speed. It
+ * is lockfree for erase operations. Elements are lazily erased on the next
+ * insert.
+ */
+namespace CuckooCache
+{
+/** bit_packed_atomic_flags implements a container for garbage collection flags
+ * that is only thread unsafe on calls to setup. This class bit-packs collection
+ * flags for memory efficiency.
+ *
+ * All operations are std::memory_order_relaxed so external mechanisms must
+ * ensure that writes and reads are properly synchronized.
+ *
+ * On setup(n), all bits up to n are marked as collected.
+ *
+ * Under the hood, because it is an 8-bit type, it makes sense to use a multiple
+ * of 8 for setup, but it will be safe if that is not the case as well.
+ *
+ */
+class bit_packed_atomic_flags
+{
+ std::unique_ptr<std::atomic<uint8_t>[]> mem;
+
+public:
+ /** No default constructor as there must be some size */
+ bit_packed_atomic_flags() = delete;
+
+ /**
+ * bit_packed_atomic_flags constructor creates memory to sufficiently
+ * keep track of garbage collection information for size entries.
+ *
+ * @param size the number of elements to allocate space for
+ *
+ * @post bit_set, bit_unset, and bit_is_set function properly forall x. x <
+ * size
+ * @post All calls to bit_is_set (without subsequent bit_unset) will return
+ * true.
+ */
+ bit_packed_atomic_flags(uint32_t size)
+ {
+ // pad out the size if needed
+ size = (size + 7) / 8;
+ mem.reset(new std::atomic<uint8_t>[size]);
+ for (uint32_t i = 0; i < size; ++i)
+ mem[i].store(0xFF);
+ };
+
+ /** setup marks all entries and ensures that bit_packed_atomic_flags can store
+ * at least size entries
+ *
+ * @param b the number of elements to allocate space for
+ * @post bit_set, bit_unset, and bit_is_set function properly forall x. x <
+ * b
+ * @post All calls to bit_is_set (without subsequent bit_unset) will return
+ * true.
+ */
+ inline void setup(uint32_t b)
+ {
+ bit_packed_atomic_flags d(b);
+ std::swap(mem, d.mem);
+ }
+
+ /** bit_set sets an entry as discardable.
+ *
+ * @param s the index of the entry to bit_set.
+ * @post immediately subsequent call (assuming proper external memory
+ * ordering) to bit_is_set(s) == true.
+ *
+ */
+ inline void bit_set(uint32_t s)
+ {
+ mem[s >> 3].fetch_or(1 << (s & 7), std::memory_order_relaxed);
+ }
+
+ /** bit_unset marks an entry as something that should not be overwritten
+ *
+ * @param s the index of the entry to bit_unset.
+ * @post immediately subsequent call (assuming proper external memory
+ * ordering) to bit_is_set(s) == false.
+ */
+ inline void bit_unset(uint32_t s)
+ {
+ mem[s >> 3].fetch_and(~(1 << (s & 7)), std::memory_order_relaxed);
+ }
+
+ /** bit_is_set queries the table for discardability at s
+ *
+ * @param s the index of the entry to read.
+ * @returns if the bit at index s was set.
+ * */
+ inline bool bit_is_set(uint32_t s) const
+ {
+ return (1 << (s & 7)) & mem[s >> 3].load(std::memory_order_relaxed);
+ }
+};
+
+/** cache implements a cache with properties similar to a cuckoo-set
+ *
+ * The cache is able to hold up to (~(uint32_t)0) - 1 elements.
+ *
+ * Read Operations:
+ * - contains(*, false)
+ *
+ * Read+Erase Operations:
+ * - contains(*, true)
+ *
+ * Erase Operations:
+ * - allow_erase()
+ *
+ * Write Operations:
+ * - setup()
+ * - setup_bytes()
+ * - insert()
+ * - please_keep()
+ *
+ * Synchronization Free Operations:
+ * - invalid()
+ * - compute_hashes()
+ *
+ * User Must Guarantee:
+ *
+ * 1) Write Requires synchronized access (e.g., a lock)
+ * 2) Read Requires no concurrent Write, synchronized with the last insert.
+ * 3) Erase requires no concurrent Write, synchronized with last insert.
+ * 4) An Erase caller must release all memory before allowing a new Writer.
+ *
+ *
+ * Note on function names:
+ * - The name "allow_erase" is used because the real discard happens later.
+ * - The name "please_keep" is used because elements may be erased anyways on insert.
+ *
+ * @tparam Element should be a movable and copyable type
+ * @tparam Hash should be a function/callable which takes a template parameter
+ * hash_select and an Element and extracts a hash from it. Should return
+ * high-entropy hashes for `Hash h; h<0>(e) ... h<7>(e)`.
+ */
+template <typename Element, typename Hash>
+class cache
+{
+private:
+ /** table stores all the elements */
+ std::vector<Element> table;
+
+ /** size stores the total available slots in the hash table */
+ uint32_t size;
+
+ /** The bit_packed_atomic_flags array is marked mutable because we want
+ * garbage collection to be allowed to occur from const methods */
+ mutable bit_packed_atomic_flags collection_flags;
+
+ /** epoch_flags tracks how recently an element was inserted into
+ * the cache. true denotes recent, false denotes not-recent. See insert()
+ * method for full semantics.
+ */
+ mutable std::vector<bool> epoch_flags;
+
+ /** epoch_heuristic_counter is used to determine when a epoch might be aged
+ * & an expensive scan should be done. epoch_heuristic_counter is
+ * decremented on insert and reset to the new number of inserts which would
+ * cause the epoch to reach epoch_size when it reaches zero.
+ */
+ uint32_t epoch_heuristic_counter;
+
+ /** epoch_size is set to be the number of elements supposed to be in a
+ * epoch. When the number of non-erased elements in a epoch
+ * exceeds epoch_size, a new epoch should be started and all
+ * current entries demoted. epoch_size is set to be 45% of size because
+ * we want to keep load around 90%, and we support 3 epochs at once --
+ * one "dead" which has been erased, one "dying" which has been marked to be
+ * erased next, and one "living" which new inserts add to.
+ */
+ uint32_t epoch_size;
+
+ /** hash_mask should be set to appropriately mask out a hash such that every
+ * masked hash is [0,size), eg, if floor(log2(size)) == 20, then hash_mask
+ * should be (1<<20)-1
+ */
+ uint32_t hash_mask;
+
+ /** depth_limit determines how many elements insert should try to replace.
+ * Should be set to log2(n)*/
+ uint8_t depth_limit;
+
+ /** hash_function is a const instance of the hash function. It cannot be
+ * static or initialized at call time as it may have internal state (such as
+ * a nonce).
+ * */
+ const Hash hash_function;
+
+ /** compute_hashes is convenience for not having to write out this
+ * expression everywhere we use the hash values of an Element.
+ *
+ * @param e the element whose hashes will be returned
+ * @returns std::array<uint32_t, 8> of deterministic hashes derived from e
+ */
+ inline std::array<uint32_t, 8> compute_hashes(const Element& e) const
+ {
+ return {{hash_function.template operator()<0>(e) & hash_mask,
+ hash_function.template operator()<1>(e) & hash_mask,
+ hash_function.template operator()<2>(e) & hash_mask,
+ hash_function.template operator()<3>(e) & hash_mask,
+ hash_function.template operator()<4>(e) & hash_mask,
+ hash_function.template operator()<5>(e) & hash_mask,
+ hash_function.template operator()<6>(e) & hash_mask,
+ hash_function.template operator()<7>(e) & hash_mask}};
+ }
+
+ /* end
+ * @returns a constexpr index that can never be inserted to */
+ constexpr uint32_t invalid() const
+ {
+ return ~(uint32_t)0;
+ }
+
+ /** allow_erase marks the element at index n as discardable. Threadsafe
+ * without any concurrent insert.
+ * @param n the index to allow erasure of
+ */
+ inline void allow_erase(uint32_t n) const
+ {
+ collection_flags.bit_set(n);
+ }
+
+ /** please_keep marks the element at index n as an entry that should be kept.
+ * Threadsafe without any concurrent insert.
+ * @param n the index to prioritize keeping
+ */
+ inline void please_keep(uint32_t n) const
+ {
+ collection_flags.bit_unset(n);
+ }
+
+ /** epoch_check handles the changing of epochs for elements stored in the
+ * cache. epoch_check should be run before every insert.
+ *
+ * First, epoch_check decrements and checks the cheap heuristic, and then does
+ * a more expensive scan if the cheap heuristic runs out. If the expensive
+ * scan suceeds, the epochs are aged and old elements are allow_erased. The
+ * cheap heuristic is reset to retrigger after the worst case growth of the
+ * current epoch's elements would exceed the epoch_size.
+ */
+ void epoch_check()
+ {
+ if (epoch_heuristic_counter != 0) {
+ --epoch_heuristic_counter;
+ return;
+ }
+ // count the number of elements from the latest epoch which
+ // have not been erased.
+ uint32_t epoch_unused_count = 0;
+ for (uint32_t i = 0; i < size; ++i)
+ epoch_unused_count += epoch_flags[i] &&
+ !collection_flags.bit_is_set(i);
+ // If there are more non-deleted entries in the current epoch than the
+ // epoch size, then allow_erase on all elements in the old epoch (marked
+ // false) and move all elements in the current epoch to the old epoch
+ // but do not call allow_erase on their indices.
+ if (epoch_unused_count >= epoch_size) {
+ for (uint32_t i = 0; i < size; ++i)
+ if (epoch_flags[i])
+ epoch_flags[i] = false;
+ else
+ allow_erase(i);
+ epoch_heuristic_counter = epoch_size;
+ } else
+ // reset the epoch_heuristic_counter to next do a scan when worst
+ // case behavior (no intermittent erases) would exceed epoch size,
+ // with a reasonable minimum scan size.
+ // Ordinarily, we would have to sanity check std::min(epoch_size,
+ // epoch_unused_count), but we already know that `epoch_unused_count
+ // < epoch_size` in this branch
+ epoch_heuristic_counter = std::max(1u, std::max(epoch_size / 16,
+ epoch_size - epoch_unused_count));
+ }
+
+public:
+ /** You must always construct a cache with some elements via a subsequent
+ * call to setup or setup_bytes, otherwise operations may segfault.
+ */
+ cache() : table(), size(), collection_flags(0), epoch_flags(),
+ epoch_heuristic_counter(), epoch_size(), depth_limit(0), hash_function()
+ {
+ }
+
+ /** setup initializes the container to store no more than new_size
+ * elements. setup rounds down to a power of two size.
+ *
+ * setup should only be called once.
+ *
+ * @param new_size the desired number of elements to store
+ * @returns the maximum number of elements storable
+ **/
+ uint32_t setup(uint32_t new_size)
+ {
+ // depth_limit must be at least one otherwise errors can occur.
+ depth_limit = static_cast<uint8_t>(std::log2(static_cast<float>(std::max((uint32_t)2, new_size))));
+ size = 1 << depth_limit;
+ hash_mask = size-1;
+ table.resize(size);
+ collection_flags.setup(size);
+ epoch_flags.resize(size);
+ // Set to 45% as described above
+ epoch_size = std::max((uint32_t)1, (45 * size) / 100);
+ // Initially set to wait for a whole epoch
+ epoch_heuristic_counter = epoch_size;
+ return size;
+ }
+
+ /** setup_bytes is a convenience function which accounts for internal memory
+ * usage when deciding how many elements to store. It isn't perfect because
+ * it doesn't account for any overhead (struct size, MallocUsage, collection
+ * and epoch flags). This was done to simplify selecting a power of two
+ * size. In the expected use case, an extra two bits per entry should be
+ * negligible compared to the size of the elements.
+ *
+ * @param bytes the approximate number of bytes to use for this data
+ * structure.
+ * @returns the maximum number of elements storable (see setup()
+ * documentation for more detail)
+ */
+ uint32_t setup_bytes(size_t bytes)
+ {
+ return setup(bytes/sizeof(Element));
+ }
+
+ /** insert loops at most depth_limit times trying to insert a hash
+ * at various locations in the table via a variant of the Cuckoo Algorithm
+ * with eight hash locations.
+ *
+ * It drops the last tried element if it runs out of depth before
+ * encountering an open slot.
+ *
+ * Thus
+ *
+ * insert(x);
+ * return contains(x, false);
+ *
+ * is not guaranteed to return true.
+ *
+ * @param e the element to insert
+ * @post one of the following: All previously inserted elements and e are
+ * now in the table, one previously inserted element is evicted from the
+ * table, the entry attempted to be inserted is evicted.
+ *
+ */
+ inline void insert(Element e)
+ {
+ epoch_check();
+ uint32_t last_loc = invalid();
+ bool last_epoch = true;
+ std::array<uint32_t, 8> locs = compute_hashes(e);
+ // Make sure we have not already inserted this element
+ // If we have, make sure that it does not get deleted
+ for (uint32_t loc : locs)
+ if (table[loc] == e) {
+ please_keep(loc);
+ epoch_flags[loc] = last_epoch;
+ return;
+ }
+ for (uint8_t depth = 0; depth < depth_limit; ++depth) {
+ // First try to insert to an empty slot, if one exists
+ for (uint32_t loc : locs) {
+ if (!collection_flags.bit_is_set(loc))
+ continue;
+ table[loc] = std::move(e);
+ please_keep(loc);
+ epoch_flags[loc] = last_epoch;
+ return;
+ }
+ /** Swap with the element at the location that was
+ * not the last one looked at. Example:
+ *
+ * 1) On first iteration, last_loc == invalid(), find returns last, so
+ * last_loc defaults to locs[0].
+ * 2) On further iterations, where last_loc == locs[k], last_loc will
+ * go to locs[k+1 % 8], i.e., next of the 8 indicies wrapping around
+ * to 0 if needed.
+ *
+ * This prevents moving the element we just put in.
+ *
+ * The swap is not a move -- we must switch onto the evicted element
+ * for the next iteration.
+ */
+ last_loc = locs[(1 + (std::find(locs.begin(), locs.end(), last_loc) - locs.begin())) & 7];
+ std::swap(table[last_loc], e);
+ // Can't std::swap a std::vector<bool>::reference and a bool&.
+ bool epoch = last_epoch;
+ last_epoch = epoch_flags[last_loc];
+ epoch_flags[last_loc] = epoch;
+
+ // Recompute the locs -- unfortunately happens one too many times!
+ locs = compute_hashes(e);
+ }
+ }
+
+ /* contains iterates through the hash locations for a given element
+ * and checks to see if it is present.
+ *
+ * contains does not check garbage collected state (in other words,
+ * garbage is only collected when the space is needed), so:
+ *
+ * insert(x);
+ * if (contains(x, true))
+ * return contains(x, false);
+ * else
+ * return true;
+ *
+ * executed on a single thread will always return true!
+ *
+ * This is a great property for re-org performance for example.
+ *
+ * contains returns a bool set true if the element was found.
+ *
+ * @param e the element to check
+ * @param erase
+ *
+ * @post if erase is true and the element is found, then the garbage collect
+ * flag is set
+ * @returns true if the element is found, false otherwise
+ */
+ inline bool contains(const Element& e, const bool erase) const
+ {
+ std::array<uint32_t, 8> locs = compute_hashes(e);
+ for (uint32_t loc : locs)
+ if (table[loc] == e) {
+ if (erase)
+ allow_erase(loc);
+ return true;
+ }
+ return false;
+ }
+};
+} // namespace CuckooCache
+
+#endif
diff --git a/src/init.cpp b/src/init.cpp
index d3efc9f978..1a500792a3 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1070,6 +1070,8 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
LogPrintf("Using config file %s\n", GetConfigFile(GetArg("-conf", BITCOIN_CONF_FILENAME)).string());
LogPrintf("Using at most %i connections (%i file descriptors available)\n", nMaxConnections, nFD);
+ InitSignatureCache();
+
LogPrintf("Using %u threads for script verification\n", nScriptCheckThreads);
if (nScriptCheckThreads) {
for (int i=0; i<nScriptCheckThreads-1; i++)
diff --git a/src/script/sigcache.cpp b/src/script/sigcache.cpp
index bdc0bfdc1c..b78d7b607f 100644
--- a/src/script/sigcache.cpp
+++ b/src/script/sigcache.cpp
@@ -11,20 +11,29 @@
#include "uint256.h"
#include "util.h"
+#include "cuckoocache.h"
#include <boost/thread.hpp>
-#include <boost/unordered_set.hpp>
namespace {
/**
* We're hashing a nonce into the entries themselves, so we don't need extra
* blinding in the set hash computation.
+ *
+ * This may exhibit platform endian dependent behavior but because these are
+ * nonced hashes (random) and this state is only ever used locally it is safe.
+ * All that matters is local consistency.
*/
-class CSignatureCacheHasher
+class SignatureCacheHasher
{
public:
- size_t operator()(const uint256& key) const {
- return key.GetCheapHash();
+ template <uint8_t hash_select>
+ uint32_t operator()(const uint256& key) const
+ {
+ static_assert(hash_select <8, "SignatureCacheHasher only has 8 hashes available.");
+ uint32_t u;
+ std::memcpy(&u, key.begin()+4*hash_select, 4);
+ return u;
}
};
@@ -38,11 +47,10 @@ class CSignatureCache
private:
//! Entries are SHA256(nonce || signature hash || public key || signature):
uint256 nonce;
- typedef boost::unordered_set<uint256, CSignatureCacheHasher> map_type;
+ typedef CuckooCache::cache<uint256, SignatureCacheHasher> map_type;
map_type setValid;
boost::shared_mutex cs_sigcache;
-
public:
CSignatureCache()
{
@@ -56,58 +64,51 @@ public:
}
bool
- Get(const uint256& entry)
+ Get(const uint256& entry, const bool erase)
{
boost::shared_lock<boost::shared_mutex> lock(cs_sigcache);
- return setValid.count(entry);
+ return setValid.contains(entry, erase);
}
- void Erase(const uint256& entry)
+ void Set(uint256& entry)
{
boost::unique_lock<boost::shared_mutex> lock(cs_sigcache);
- setValid.erase(entry);
+ setValid.insert(entry);
}
-
- void Set(const uint256& entry)
+ uint32_t setup_bytes(size_t n)
{
- size_t nMaxCacheSize = GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
- if (nMaxCacheSize <= 0) return;
-
- boost::unique_lock<boost::shared_mutex> lock(cs_sigcache);
- while (memusage::DynamicUsage(setValid) > nMaxCacheSize)
- {
- map_type::size_type s = GetRand(setValid.bucket_count());
- map_type::local_iterator it = setValid.begin(s);
- if (it != setValid.end(s)) {
- setValid.erase(*it);
- }
- }
-
- setValid.insert(entry);
+ return setValid.setup_bytes(n);
}
};
+/* In previous versions of this code, signatureCache was a local static variable
+ * in CachingTransactionSignatureChecker::VerifySignature. We initialize
+ * signatureCache outside of VerifySignature to avoid the atomic operation per
+ * call overhead associated with local static variables even though
+ * signatureCache could be made local to VerifySignature.
+*/
+static CSignatureCache signatureCache;
}
-bool CachingTransactionSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
+// To be called once in AppInit2/TestingSetup to initialize the signatureCache
+void InitSignatureCache()
{
- static CSignatureCache signatureCache;
+ size_t nMaxCacheSize = GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
+ if (nMaxCacheSize <= 0) return;
+ size_t nElems = signatureCache.setup_bytes(nMaxCacheSize);
+ LogPrintf("Using %zu MiB out of %zu requested for signature cache, able to store %zu elements\n",
+ (nElems*sizeof(uint256)) >>20, nMaxCacheSize>>20, nElems);
+}
+bool CachingTransactionSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
+{
uint256 entry;
signatureCache.ComputeEntry(entry, sighash, vchSig, pubkey);
-
- if (signatureCache.Get(entry)) {
- if (!store) {
- signatureCache.Erase(entry);
- }
+ if (signatureCache.Get(entry, !store))
return true;
- }
-
if (!TransactionSignatureChecker::VerifySignature(vchSig, pubkey, sighash))
return false;
-
- if (store) {
+ if (store)
signatureCache.Set(entry);
- }
return true;
}
diff --git a/src/script/sigcache.h b/src/script/sigcache.h
index 44551ec2bc..5243fc0a42 100644
--- a/src/script/sigcache.h
+++ b/src/script/sigcache.h
@@ -10,9 +10,10 @@
#include <vector>
-// DoS prevention: limit cache size to less than 40MB (over 500000
-// entries on 64-bit systems).
-static const unsigned int DEFAULT_MAX_SIG_CACHE_SIZE = 40;
+// DoS prevention: limit cache size to 32MB (over 1000000 entries on 64-bit
+// systems). Due to how we count cache size, actual memory usage is slightly
+// more (~32.25 MB)
+static const unsigned int DEFAULT_MAX_SIG_CACHE_SIZE = 32;
class CPubKey;
@@ -27,4 +28,6 @@ public:
bool VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& vchPubKey, const uint256& sighash) const;
};
+void InitSignatureCache();
+
#endif // BITCOIN_SCRIPT_SIGCACHE_H
diff --git a/src/test/test_bitcoin.cpp b/src/test/test_bitcoin.cpp
index 98f4ed939f..b7a2a854d3 100644
--- a/src/test/test_bitcoin.cpp
+++ b/src/test/test_bitcoin.cpp
@@ -19,6 +19,7 @@
#include "ui_interface.h"
#include "rpc/server.h"
#include "rpc/register.h"
+#include "script/sigcache.h"
#include "test/testutil.h"
@@ -39,6 +40,7 @@ BasicTestingSetup::BasicTestingSetup(const std::string& chainName)
ECC_Start();
SetupEnvironment();
SetupNetworking();
+ InitSignatureCache();
fPrintToDebugLog = false; // don't want to write to debug.log file
fCheckBlockIndex = true;
SelectParams(chainName);
generated by cgit v1.2.3 (git 2.26.2) at 2024-07-05 02:38:04 +0000