2 * Copyright 2013 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef FOLLY_MEMORYMAPPING_H_
18 #define FOLLY_MEMORYMAPPING_H_
20 #include "folly/FBString.h"
21 #include "folly/File.h"
22 #include "folly/Range.h"
23 #include <glog/logging.h>
24 #include <boost/noncopyable.hpp>
29 * Maps files in memory (read-only).
31 * @author Tudor Bosman (tudorb@fb.com)
33 class MemoryMapping : boost::noncopyable {
36 * Lock the pages in memory?
37 * TRY_LOCK = try to lock, log warning if permission denied
38 * MUST_LOCK = lock, fail assertion if permission denied.
45 * Map a portion of the file indicated by filename in memory, causing a CHECK
48 * By default, map the whole file. length=-1: map from offset to EOF.
49 * Unlike the mmap() system call, offset and length don't need to be
50 * page-aligned. length is clipped to the end of the file if it's too large.
52 * The mapping will be destroyed (and the memory pointed-to by data() will
53 * likely become inaccessible) when the MemoryMapping object is destroyed.
55 explicit MemoryMapping(File file,
59 virtual ~MemoryMapping();
62 * Lock the pages in memory
64 bool mlock(LockMode lock);
68 * If dontneed is true, the kernel is instructed to release these pages
69 * (per madvise(MADV_DONTNEED)).
71 void munlock(bool dontneed=false);
74 * Hint that these pages will be scanned linearly.
75 * madvise(MADV_SEQUENTIAL)
77 void hintLinearScan();
80 * Advise the kernel about memory access.
82 void advise(int advice) const;
85 * A bitwise cast of the mapped bytes as range of values. Only intended for
86 * use with POD or in-place usable types.
89 Range<const T*> asRange() const {
90 size_t count = data_.size() / sizeof(T);
91 return Range<const T*>(static_cast<const T*>(
92 static_cast<const void*>(data_.data())),
97 * A range of bytes mapped by this mapping.
99 Range<const uint8_t*> range() const {
100 return {data_.begin(), data_.end()};
104 * Return the memory area where the file was mapped.
106 StringPiece data() const {
107 return asRange<const char>();
110 bool mlocked() const {
114 int fd() const { return file_.fd(); }
120 off_t offset, off_t length,
128 Range<uint8_t*> data_;
132 * Maps files in memory for writing.
134 * @author Tom Jackson (tjackson@fb.com)
136 class WritableMemoryMapping : public MemoryMapping {
138 explicit WritableMemoryMapping(File file,
142 * A bitwise cast of the mapped bytes as range of mutable values. Only
143 * intended for use with POD or in-place usable types.
146 Range<T*> asWritableRange() const {
147 size_t count = data_.size() / sizeof(T);
148 return Range<T*>(static_cast<T*>(
149 static_cast<void*>(data_.data())),
154 * A range of mutable bytes mapped by this mapping.
156 Range<uint8_t*> writableRange() const {
163 #endif /* FOLLY_MEMORYMAPPING_H_ */