unit-map.h
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//===-- runtime/unit-map.h --------------------------------------*- 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
//
//===----------------------------------------------------------------------===//
// Maps Fortran unit numbers to their ExternalFileUnit instances.
// A simple hash table with forward-linked chains per bucket.
#ifndef FORTRAN_RUNTIME_UNIT_MAP_H_
#define FORTRAN_RUNTIME_UNIT_MAP_H_
#include "lock.h"
#include "memory.h"
#include "unit.h"
#include <cstdlib>
namespace Fortran::runtime::io {
class UnitMap {
public:
ExternalFileUnit *LookUp(int n) {
CriticalSection critical{lock_};
return Find(n);
}
ExternalFileUnit &LookUpOrCreate(
int n, const Terminator &terminator, bool &wasExtant) {
CriticalSection critical{lock_};
auto *p{Find(n)};
wasExtant = p != nullptr;
return p ? *p : Create(n, terminator);
}
ExternalFileUnit &NewUnit(const Terminator &terminator) {
CriticalSection critical{lock_};
return Create(nextNewUnit_--, terminator);
}
// To prevent races, the unit is removed from the map if it exists,
// and put on the closing_ list until DestroyClosed() is called.
ExternalFileUnit *LookUpForClose(int);
void DestroyClosed(ExternalFileUnit &);
void CloseAll(IoErrorHandler &);
void FlushAll(IoErrorHandler &);
private:
struct Chain {
explicit Chain(int n) : unit{n} {}
ExternalFileUnit unit;
OwningPtr<Chain> next{nullptr};
};
static constexpr int buckets_{1031}; // must be prime
int Hash(int n) { return std::abs(n) % buckets_; }
ExternalFileUnit *Find(int n) {
Chain *previous{nullptr};
int hash{Hash(n)};
for (Chain *p{bucket_[hash].get()}; p; previous = p, p = p->next.get()) {
if (p->unit.unitNumber() == n) {
if (previous) {
// Move found unit to front of chain for quicker lookup next time
previous->next.swap(p->next); // now p->next.get() == p
bucket_[hash].swap(p->next); // now bucket_[hash].get() == p
}
return &p->unit;
}
}
return nullptr;
}
ExternalFileUnit &Create(int, const Terminator &);
Lock lock_;
OwningPtr<Chain> bucket_[buckets_]{}; // all owned by *this
int nextNewUnit_{-1000}; // see 12.5.6.12 in Fortran 2018
OwningPtr<Chain> closing_{nullptr}; // units during CLOSE statement
};
} // namespace Fortran::runtime::io
#endif // FORTRAN_RUNTIME_UNIT_MAP_H_