FileSystemStatCache.h

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//===--- FileSystemStatCache.h - Caching for 'stat' calls -------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file defines the FileSystemStatCache interface.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_FILESYSTEMSTATCACHE_H
#define LLVM_CLANG_FILESYSTEMSTATCACHE_H

#include "clang/Basic/LLVM.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/ADT/StringMap.h"
#include <sys/types.h>
#include <sys/stat.h>

namespace clang {

/// \brief Abstract interface for introducing a FileManager cache for 'stat'
/// system calls, which is used by precompiled and pretokenized headers to
/// improve performance.
class FileSystemStatCache {
  virtual void anchor();
protected:
  OwningPtr<FileSystemStatCache> NextStatCache;
  
public:
  virtual ~FileSystemStatCache() {}
  
  enum LookupResult {
    CacheExists,   //< We know the file exists and its cached stat data.
    CacheMissing   //< We know that the file doesn't exist.
  };

  /// FileSystemStatCache::get - Get the 'stat' information for the specified
  /// path, using the cache to accellerate it if possible.  This returns true if
  /// the path does not exist or false if it exists.
  ///
  /// If FileDescriptor is non-null, then this lookup should only return success
  /// for files (not directories).  If it is null this lookup should only return
  /// success for directories (not files).  On a successful file lookup, the
  /// implementation can optionally fill in FileDescriptor with a valid
  /// descriptor and the client guarantees that it will close it.
  static bool get(const char *Path, struct stat &StatBuf, int *FileDescriptor,
                  FileSystemStatCache *Cache);
  
  
  /// \brief Sets the next stat call cache in the chain of stat caches.
  /// Takes ownership of the given stat cache.
  void setNextStatCache(FileSystemStatCache *Cache) {
    NextStatCache.reset(Cache);
  }
  
  /// \brief Retrieve the next stat call cache in the chain.
  FileSystemStatCache *getNextStatCache() { return NextStatCache.get(); }
  
  /// \brief Retrieve the next stat call cache in the chain, transferring
  /// ownership of this cache (and, transitively, all of the remaining caches)
  /// to the caller.
  FileSystemStatCache *takeNextStatCache() { return NextStatCache.take(); }
  
protected:
  virtual LookupResult getStat(const char *Path, struct stat &StatBuf,
                               int *FileDescriptor) = 0;

  LookupResult statChained(const char *Path, struct stat &StatBuf,
                           int *FileDescriptor) {
    if (FileSystemStatCache *Next = getNextStatCache())
      return Next->getStat(Path, StatBuf, FileDescriptor);
    
    // If we hit the end of the list of stat caches to try, just compute and
    // return it without a cache.
    return get(Path, StatBuf, FileDescriptor, 0) ? CacheMissing : CacheExists;
  }
};

/// \brief A stat "cache" that can be used by FileManager to keep
/// track of the results of stat() calls that occur throughout the
/// execution of the front end.
class MemorizeStatCalls : public FileSystemStatCache {
public:
  /// \brief The set of stat() calls that have been seen.
  llvm::StringMap<struct stat, llvm::BumpPtrAllocator> StatCalls;
  
  typedef llvm::StringMap<struct stat, llvm::BumpPtrAllocator>::const_iterator
  iterator;
  
  iterator begin() const { return StatCalls.begin(); }
  iterator end() const { return StatCalls.end(); }
  
  virtual LookupResult getStat(const char *Path, struct stat &StatBuf,
                               int *FileDescriptor);
};

} // end namespace clang

#endif