Add exclusive flag to MemoryMappedFile

modules/juce_core/files/juce_File.cpp

@@ -966,16 +966,16 @@ bool File::createSymbolicLink (const File& linkFileToCreate, bool overwriteExist
 }
 
 //==============================================================================
-MemoryMappedFile::MemoryMappedFile (const File& file, MemoryMappedFile::AccessMode mode)
+MemoryMappedFile::MemoryMappedFile (const File& file, MemoryMappedFile::AccessMode mode, bool exclusive)
     : address (nullptr), range (0, file.getSize()), fileHandle (0)
 {
-    openInternal (file, mode);
+    openInternal (file, mode, exclusive);
 }
 
-MemoryMappedFile::MemoryMappedFile (const File& file, const Range<int64>& fileRange, AccessMode mode)
+MemoryMappedFile::MemoryMappedFile (const File& file, const Range<int64>& fileRange, AccessMode mode, bool exclusive)
     : address (nullptr), range (fileRange.getIntersectionWith (Range<int64> (0, file.getSize()))), fileHandle (0)
 {
-    openInternal (file, mode);
+    openInternal (file, mode, exclusive);
 }
 
 

modules/juce_core/files/juce_MemoryMappedFile.h

@@ -56,8 +56,13 @@ public:
         will lazily pull the data into memory when blocks are accessed.
 
         If the file can't be opened for some reason, the getData() method will return a null pointer.
+
+        If exclusive is false then other apps can also open the same memory mapped file and use this
+        mapping as an effective way of communicating. If exclusive is true then the mapped file will
+        be opened exclusively - preventing other apps to access the file which may improve the
+        performance of accessing the file.
     */
-    MemoryMappedFile (const File& file, AccessMode mode);
+    MemoryMappedFile (const File& file, AccessMode mode, bool exclusive = false);
 
     /** Opens a section of a file and maps it to an area of virtual memory.
 
@@ -77,7 +82,8 @@ public:
     */
     MemoryMappedFile (const File& file,
                       const Range<int64>& fileRange,
-                      AccessMode mode);
+                      AccessMode mode,
+                      bool exclusive = false);
 
     /** Destructor. */
     ~MemoryMappedFile();
@@ -106,7 +112,7 @@ private:
     int fileHandle;
    #endif
 
-    void openInternal (const File&, AccessMode);
+    void openInternal (const File&, AccessMode, bool);
 
     JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (MemoryMappedFile)
 };

modules/juce_core/native/juce_posix_SharedCode.h

@@ -586,7 +586,7 @@ String SystemStats::getEnvironmentVariable (const String& name, const String& de
 }
 
 //==============================================================================
-void MemoryMappedFile::openInternal (const File& file, AccessMode mode)
+void MemoryMappedFile::openInternal (const File& file, AccessMode mode, bool exclusive)
 {
     jassert (mode == readOnly || mode == readWrite);
 
@@ -603,7 +603,7 @@ void MemoryMappedFile::openInternal (const File& file, AccessMode mode)
     {
         void* m = mmap (0, (size_t) range.getLength(),
                         mode == readWrite ? (PROT_READ | PROT_WRITE) : PROT_READ,
-                        MAP_SHARED, fileHandle,
+                        exclusive ? MAP_PRIVATE : MAP_SHARED, fileHandle,
                         (off_t) range.getStart());
 
         if (m != MAP_FAILED)

modules/juce_core/native/juce_win32_Files.cpp

@@ -325,7 +325,7 @@ Result FileOutputStream::truncate()
 }
 
 //==============================================================================
-void MemoryMappedFile::openInternal (const File& file, AccessMode mode)
+void MemoryMappedFile::openInternal (const File& file, AccessMode mode, bool exclusive)
 {
     jassert (mode == readOnly || mode == readWrite);
 
@@ -348,7 +348,8 @@ void MemoryMappedFile::openInternal (const File& file, AccessMode mode)
         access = FILE_MAP_ALL_ACCESS;
     }
 
-    HANDLE h = CreateFile (file.getFullPathName().toWideCharPointer(), accessMode, FILE_SHARE_READ, 0,
+    HANDLE h = CreateFile (file.getFullPathName().toWideCharPointer(), accessMode,
+                           exclusive ? 0 : (FILE_SHARE_READ | (mode == readWrite ? FILE_SHARE_WRITE : 0)), 0,
                            createType, FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, 0);
 
     if (h != INVALID_HANDLE_VALUE)