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Unified Diff: base/files/memory_mapped_file.h

Issue 1798203002: Support read/write memory-mapped files. (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master
Patch Set: rebased Created 4 years, 7 months ago
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Index: base/files/memory_mapped_file.h
diff --git a/base/files/memory_mapped_file.h b/base/files/memory_mapped_file.h
index 6362e765cb4ba8c808f3be7f214772844b2d218a..cad99f679d7301cdd5fb028517e385c51133ba69 100644
--- a/base/files/memory_mapped_file.h
+++ b/base/files/memory_mapped_file.h
@@ -23,6 +23,29 @@ class FilePath;
class BASE_EXPORT MemoryMappedFile {
public:
+ enum Access {
+ // Mapping a file into memory effectively allows for file I/O on any thread.
+ // The accessing thread could be paused while data from the file is paged
+ // into memory. Worse, a corrupted filesystem could cause a SEGV within the
+ // program instead of just an I/O error.
+ READ_ONLY,
+
+ // This provides read/write access to a file and must be used with care of
+ // the additional subtleties involved in doing so. Though the OS will do
+ // the writing of data on its own time, too many dirty pages can cause
+ // the OS to pause the thread while it writes them out. The pause can
+ // be as much as 1s on some systems.
+ READ_WRITE,
+
+ // This provides read/write access but with the ability to write beyond
+ // the end of the existing file up to a maximum size specified as the
+ // "region". Depending on the OS, the file may or may not be immediately
+ // extended to the maximum size though it won't be loaded in RAM until
+ // needed. Note, however, that the maximum size will still be reserved
+ // in the process address space.
+ READ_WRITE_EXTEND,
+ };
+
// The default constructor sets all members to invalid/null values.
MemoryMappedFile();
~MemoryMappedFile();
@@ -41,27 +64,37 @@ class BASE_EXPORT MemoryMappedFile {
int64_t size;
};
- // Opens an existing file and maps it into memory. Access is restricted to
- // read only. If this object already points to a valid memory mapped file
- // then this method will fail and return false. If it cannot open the file,
- // the file does not exist, or the memory mapping fails, it will return false.
- // Later we may want to allow the user to specify access.
- bool Initialize(const FilePath& file_name);
-
- // As above, but works with an already-opened file. MemoryMappedFile takes
- // ownership of |file| and closes it when done.
- bool Initialize(File file);
-
- // As above, but works with a region of an already-opened file.
- bool Initialize(File file, const Region& region);
-
-#if defined(OS_WIN)
- // Opens an existing file and maps it as an image section. Please refer to
- // the Initialize function above for additional information.
- bool InitializeAsImageSection(const FilePath& file_name);
-#endif // OS_WIN
+ // Opens an existing file and maps it into memory. |access| can be read-only
+ // or read/write but not read/write+extend. If this object already points
+ // to a valid memory mapped file then this method will fail and return
+ // false. If it cannot open the file, the file does not exist, or the
+ // memory mapping fails, it will return false.
+ bool Initialize(const FilePath& file_name, Access access);
+ bool Initialize(const FilePath& file_name) {
+ return Initialize(file_name, READ_ONLY);
+ }
+
+ // As above, but works with an already-opened file. |access| can be read-only
+ // or read/write but not read/write+extend. MemoryMappedFile takes ownership
+ // of |file| and closes it when done. |file| must have been opened with
+ // permissions suitable for |access|. If the memory mapping fails, it will
+ // return false.
+ bool Initialize(File file, Access access);
+ bool Initialize(File file) {
+ return Initialize(std::move(file), READ_ONLY);
+ }
+
+ // As above, but works with a region of an already-opened file. All forms of
+ // |access| are allowed. If READ_WRITE_EXTEND is specified then |region|
+ // provides the maximum size of the file. If the memory mapping fails, it
+ // return false.
+ bool Initialize(File file, const Region& region, Access access);
+ bool Initialize(File file, const Region& region) {
+ return Initialize(std::move(file), region, READ_ONLY);
+ }
const uint8_t* data() const { return data_; }
+ uint8_t* data() { return data_; }
size_t length() const { return length_; }
// Is file_ a valid file handle that points to an open, memory mapped file?
@@ -82,7 +115,7 @@ class BASE_EXPORT MemoryMappedFile {
// Map the file to memory, set data_ to that memory address. Return true on
// success, false on any kind of failure. This is a helper for Initialize().
- bool MapFileRegionToMemory(const Region& region);
+ bool MapFileRegionToMemory(const Region& region, Access access);
// Closes all open handles.
void CloseHandles();
@@ -93,7 +126,6 @@ class BASE_EXPORT MemoryMappedFile {
#if defined(OS_WIN)
win::ScopedHandle file_mapping_;
- bool image_; // Map as an image.
#endif
DISALLOW_COPY_AND_ASSIGN(MemoryMappedFile);
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