clang  6.0.0svn
MemoryBufferCache.h
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1 //===- MemoryBufferCache.h - Cache for loaded memory buffers ----*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef LLVM_CLANG_BASIC_MEMORYBUFFERCACHE_H
11 #define LLVM_CLANG_BASIC_MEMORYBUFFERCACHE_H
12 
13 #include "llvm/ADT/IntrusiveRefCntPtr.h"
14 #include "llvm/ADT/StringMap.h"
15 #include <memory>
16 
17 namespace llvm {
18 class MemoryBuffer;
19 } // end namespace llvm
20 
21 namespace clang {
22 
23 /// Manage memory buffers across multiple users.
24 ///
25 /// Ensures that multiple users have a consistent view of each buffer. This is
26 /// used by \a CompilerInstance when building PCMs to ensure that each \a
27 /// ModuleManager sees the same files.
28 ///
29 /// \a finalizeCurrentBuffers() should be called before creating a new user.
30 /// This locks in the current buffers, ensuring that no buffer that has already
31 /// been accessed can be purged, preventing use-after-frees.
32 class MemoryBufferCache : public llvm::RefCountedBase<MemoryBufferCache> {
33  struct BufferEntry {
34  std::unique_ptr<llvm::MemoryBuffer> Buffer;
35 
36  /// Track the timeline of when this was added to the cache.
37  unsigned Index;
38  };
39 
40  /// Cache of buffers.
41  llvm::StringMap<BufferEntry> Buffers;
42 
43  /// Monotonically increasing index.
44  unsigned NextIndex = 0;
45 
46  /// Bumped to prevent "older" buffers from being removed.
47  unsigned FirstRemovableIndex = 0;
48 
49 public:
50  /// Store the Buffer under the Filename.
51  ///
52  /// \pre There is not already buffer is not already in the cache.
53  /// \return a reference to the buffer as a convenience.
54  llvm::MemoryBuffer &addBuffer(llvm::StringRef Filename,
55  std::unique_ptr<llvm::MemoryBuffer> Buffer);
56 
57  /// Try to remove a buffer from the cache.
58  ///
59  /// \return false on success, iff \c !isBufferFinal().
60  bool tryToRemoveBuffer(llvm::StringRef Filename);
61 
62  /// Get a pointer to the buffer if it exists; else nullptr.
63  llvm::MemoryBuffer *lookupBuffer(llvm::StringRef Filename);
64 
65  /// Check whether the buffer is final.
66  ///
67  /// \return true iff \a finalizeCurrentBuffers() has been called since the
68  /// buffer was added. This prevents buffers from being removed.
69  bool isBufferFinal(llvm::StringRef Filename);
70 
71  /// Finalize the current buffers in the cache.
72  ///
73  /// Should be called when creating a new user to ensure previous uses aren't
74  /// invalidated.
75  void finalizeCurrentBuffers();
76 };
77 
78 } // end namespace clang
79 
80 #endif // LLVM_CLANG_BASIC_MEMORYBUFFERCACHE_H
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Manage memory buffers across multiple users.
StringRef Filename
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