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//===- SymbolStringPool.h - Multi-threaded pool for JIT symbols -*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Contains a multi-threaded string pool suitable for use with ORC.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_EXECUTIONENGINE_ORC_SYMBOLSTRINGPOOL_H
#define LLVM_EXECUTIONENGINE_ORC_SYMBOLSTRINGPOOL_H
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/StringMap.h"
#include <atomic>
#include <mutex>
namespace llvm {
namespace orc {
class SymbolStringPtr;
/// String pool for symbol names used by the JIT.
class SymbolStringPool {
friend class SymbolStringPtr;
public:
/// Destroy a SymbolStringPool.
~SymbolStringPool();
/// Create a symbol string pointer from the given string.
SymbolStringPtr intern(StringRef S);
/// Remove from the pool any entries that are no longer referenced.
void clearDeadEntries();
/// Returns true if the pool is empty.
bool empty() const;
private:
using RefCountType = std::atomic<size_t>;
using PoolMap = StringMap<RefCountType>;
using PoolMapEntry = StringMapEntry<RefCountType>;
mutable std::mutex PoolMutex;
PoolMap Pool;
};
/// Pointer to a pooled string representing a symbol name.
class SymbolStringPtr {
friend class OrcV2CAPIHelper;
friend class SymbolStringPool;
friend struct DenseMapInfo<SymbolStringPtr>;
public:
SymbolStringPtr() = default;
SymbolStringPtr(std::nullptr_t) {}
SymbolStringPtr(const SymbolStringPtr &Other)
: S(Other.S) {
if (isRealPoolEntry(S))
++S->getValue();
}
SymbolStringPtr& operator=(const SymbolStringPtr &Other) {
if (isRealPoolEntry(S)) {
assert(S->getValue() && "Releasing SymbolStringPtr with zero ref count");
--S->getValue();
}
S = Other.S;
if (isRealPoolEntry(S))
++S->getValue();
return *this;
}
SymbolStringPtr(SymbolStringPtr &&Other) : S(nullptr) {
std::swap(S, Other.S);
}
SymbolStringPtr& operator=(SymbolStringPtr &&Other) {
if (isRealPoolEntry(S)) {
assert(S->getValue() && "Releasing SymbolStringPtr with zero ref count");
--S->getValue();
}
S = nullptr;
std::swap(S, Other.S);
return *this;
}
~SymbolStringPtr() {
if (isRealPoolEntry(S)) {
assert(S->getValue() && "Releasing SymbolStringPtr with zero ref count");
--S->getValue();
}
}
explicit operator bool() const { return S; }
StringRef operator*() const { return S->first(); }
friend bool operator==(const SymbolStringPtr &LHS,
const SymbolStringPtr &RHS) {
return LHS.S == RHS.S;
}
friend bool operator!=(const SymbolStringPtr &LHS,
const SymbolStringPtr &RHS) {
return !(LHS == RHS);
}
friend bool operator<(const SymbolStringPtr &LHS,
const SymbolStringPtr &RHS) {
return LHS.S < RHS.S;
}
private:
using PoolEntry = SymbolStringPool::PoolMapEntry;
using PoolEntryPtr = PoolEntry *;
SymbolStringPtr(SymbolStringPool::PoolMapEntry *S)
: S(S) {
if (isRealPoolEntry(S))
++S->getValue();
}
// Returns false for null, empty, and tombstone values, true otherwise.
bool isRealPoolEntry(PoolEntryPtr P) {
return ((reinterpret_cast<uintptr_t>(P) - 1) & InvalidPtrMask) !=
InvalidPtrMask;
}
static SymbolStringPtr getEmptyVal() {
return SymbolStringPtr(reinterpret_cast<PoolEntryPtr>(EmptyBitPattern));
}
static SymbolStringPtr getTombstoneVal() {
return SymbolStringPtr(reinterpret_cast<PoolEntryPtr>(TombstoneBitPattern));
}
constexpr static uintptr_t EmptyBitPattern =
std::numeric_limits<uintptr_t>::max()
<< PointerLikeTypeTraits<PoolEntryPtr>::NumLowBitsAvailable;
constexpr static uintptr_t TombstoneBitPattern =
(std::numeric_limits<uintptr_t>::max() - 1)
<< PointerLikeTypeTraits<PoolEntryPtr>::NumLowBitsAvailable;
constexpr static uintptr_t InvalidPtrMask =
(std::numeric_limits<uintptr_t>::max() - 3)
<< PointerLikeTypeTraits<PoolEntryPtr>::NumLowBitsAvailable;
PoolEntryPtr S = nullptr;
};
inline SymbolStringPool::~SymbolStringPool() {
#ifndef NDEBUG
clearDeadEntries();
assert(Pool.empty() && "Dangling references at pool destruction time");
#endif // NDEBUG
}
inline SymbolStringPtr SymbolStringPool::intern(StringRef S) {
std::lock_guard<std::mutex> Lock(PoolMutex);
PoolMap::iterator I;
bool Added;
std::tie(I, Added) = Pool.try_emplace(S, 0);
return SymbolStringPtr(&*I);
}
inline void SymbolStringPool::clearDeadEntries() {
std::lock_guard<std::mutex> Lock(PoolMutex);
for (auto I = Pool.begin(), E = Pool.end(); I != E;) {
auto Tmp = I++;
if (Tmp->second == 0)
Pool.erase(Tmp);
}
}
inline bool SymbolStringPool::empty() const {
std::lock_guard<std::mutex> Lock(PoolMutex);
return Pool.empty();
}
} // end namespace orc
template <>
struct DenseMapInfo<orc::SymbolStringPtr> {
static orc::SymbolStringPtr getEmptyKey() {
return orc::SymbolStringPtr::getEmptyVal();
}
static orc::SymbolStringPtr getTombstoneKey() {
return orc::SymbolStringPtr::getTombstoneVal();
}
static unsigned getHashValue(const orc::SymbolStringPtr &V) {
return DenseMapInfo<orc::SymbolStringPtr::PoolEntryPtr>::getHashValue(V.S);
}
static bool isEqual(const orc::SymbolStringPtr &LHS,
const orc::SymbolStringPtr &RHS) {
return LHS.S == RHS.S;
}
};
} // end namespace llvm
#endif // LLVM_EXECUTIONENGINE_ORC_SYMBOLSTRINGPOOL_H
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