New class: MemoryMappedFile.

Builds/MacOSX/Juce.xcodeproj/project.pbxproj

@@ -898,6 +898,7 @@
 		4EEF0B0BB4C3D1956B04122B = { isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = juce_FileOutputStream.h; path = ../../src/io/files/juce_FileOutputStream.h; sourceTree = SOURCE_ROOT; };
 		59B2FFF817679AEA84375E1B = { isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; name = juce_FileSearchPath.cpp; path = ../../src/io/files/juce_FileSearchPath.cpp; sourceTree = SOURCE_ROOT; };
 		49BF2B02A6D7B4438FC24839 = { isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = juce_FileSearchPath.h; path = ../../src/io/files/juce_FileSearchPath.h; sourceTree = SOURCE_ROOT; };
+		00B348FA35A7F691AEF84FBA = { isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = juce_MemoryMappedFile.h; path = ../../src/io/files/juce_MemoryMappedFile.h; sourceTree = SOURCE_ROOT; };
 		D9B3C04F8EB4228DD59002E7 = { isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; name = juce_NamedPipe.cpp; path = ../../src/io/files/juce_NamedPipe.cpp; sourceTree = SOURCE_ROOT; };
 		42DA88264F768BAACD0414A3 = { isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = juce_NamedPipe.h; path = ../../src/io/files/juce_NamedPipe.h; sourceTree = SOURCE_ROOT; };
 		17C3AF03FF7AE88AE0C73311 = { isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; name = juce_TemporaryFile.cpp; path = ../../src/io/files/juce_TemporaryFile.cpp; sourceTree = SOURCE_ROOT; };
@@ -1713,6 +1714,7 @@
 				4EEF0B0BB4C3D1956B04122B,
 				59B2FFF817679AEA84375E1B,
 				49BF2B02A6D7B4438FC24839,
+				00B348FA35A7F691AEF84FBA,
 				D9B3C04F8EB4228DD59002E7,
 				42DA88264F768BAACD0414A3,
 				17C3AF03FF7AE88AE0C73311,

Builds/VisualStudio2005/Juce.vcproj

@@ -787,6 +787,7 @@
             <File RelativePath="..\..\src\io\files\juce_FileOutputStream.h"/>
             <File RelativePath="..\..\src\io\files\juce_FileSearchPath.cpp"/>
             <File RelativePath="..\..\src\io\files\juce_FileSearchPath.h"/>
+            <File RelativePath="..\..\src\io\files\juce_MemoryMappedFile.h"/>
             <File RelativePath="..\..\src\io\files\juce_NamedPipe.cpp"/>
             <File RelativePath="..\..\src\io\files\juce_NamedPipe.h"/>
             <File RelativePath="..\..\src\io\files\juce_TemporaryFile.cpp"/>

Builds/VisualStudio2008/Juce.vcproj

@@ -787,6 +787,7 @@
             <File RelativePath="..\..\src\io\files\juce_FileOutputStream.h"/>
             <File RelativePath="..\..\src\io\files\juce_FileSearchPath.cpp"/>
             <File RelativePath="..\..\src\io\files\juce_FileSearchPath.h"/>
+            <File RelativePath="..\..\src\io\files\juce_MemoryMappedFile.h"/>
             <File RelativePath="..\..\src\io\files\juce_NamedPipe.cpp"/>
             <File RelativePath="..\..\src\io\files\juce_NamedPipe.h"/>
             <File RelativePath="..\..\src\io\files\juce_TemporaryFile.cpp"/>

Builds/VisualStudio2008_DLL/Juce.vcproj

@@ -789,6 +789,7 @@
             <File RelativePath="..\..\src\io\files\juce_FileOutputStream.h"/>
             <File RelativePath="..\..\src\io\files\juce_FileSearchPath.cpp"/>
             <File RelativePath="..\..\src\io\files\juce_FileSearchPath.h"/>
+            <File RelativePath="..\..\src\io\files\juce_MemoryMappedFile.h"/>
             <File RelativePath="..\..\src\io\files\juce_NamedPipe.cpp"/>
             <File RelativePath="..\..\src\io\files\juce_NamedPipe.h"/>
             <File RelativePath="..\..\src\io\files\juce_TemporaryFile.cpp"/>

Builds/VisualStudio2010/Juce.vcxproj

@@ -741,6 +741,7 @@
     <ClInclude Include="..\..\src\io\files\juce_FileInputStream.h"/>
     <ClInclude Include="..\..\src\io\files\juce_FileOutputStream.h"/>
     <ClInclude Include="..\..\src\io\files\juce_FileSearchPath.h"/>
+    <ClInclude Include="..\..\src\io\files\juce_MemoryMappedFile.h"/>
     <ClInclude Include="..\..\src\io\files\juce_NamedPipe.h"/>
     <ClInclude Include="..\..\src\io\files\juce_TemporaryFile.h"/>
     <ClInclude Include="..\..\src\io\files\juce_ZipFile.h"/>

Builds/VisualStudio2010/Juce.vcxproj.filters

@@ -2154,6 +2154,9 @@
     <ClInclude Include="..\..\src\io\files\juce_FileSearchPath.h">
       <Filter>Juce\Source\io\files</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\src\io\files\juce_MemoryMappedFile.h">
+      <Filter>Juce\Source\io\files</Filter>
+    </ClInclude>
     <ClInclude Include="..\..\src\io\files\juce_NamedPipe.h">
       <Filter>Juce\Source\io\files</Filter>
     </ClInclude>

Builds/iOS/Juce.xcodeproj/project.pbxproj

@@ -898,6 +898,7 @@
 		4EEF0B0BB4C3D1956B04122B = { isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = juce_FileOutputStream.h; path = ../../src/io/files/juce_FileOutputStream.h; sourceTree = SOURCE_ROOT; };
 		59B2FFF817679AEA84375E1B = { isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; name = juce_FileSearchPath.cpp; path = ../../src/io/files/juce_FileSearchPath.cpp; sourceTree = SOURCE_ROOT; };
 		49BF2B02A6D7B4438FC24839 = { isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = juce_FileSearchPath.h; path = ../../src/io/files/juce_FileSearchPath.h; sourceTree = SOURCE_ROOT; };
+		00B348FA35A7F691AEF84FBA = { isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = juce_MemoryMappedFile.h; path = ../../src/io/files/juce_MemoryMappedFile.h; sourceTree = SOURCE_ROOT; };
 		D9B3C04F8EB4228DD59002E7 = { isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; name = juce_NamedPipe.cpp; path = ../../src/io/files/juce_NamedPipe.cpp; sourceTree = SOURCE_ROOT; };
 		42DA88264F768BAACD0414A3 = { isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = juce_NamedPipe.h; path = ../../src/io/files/juce_NamedPipe.h; sourceTree = SOURCE_ROOT; };
 		17C3AF03FF7AE88AE0C73311 = { isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; name = juce_TemporaryFile.cpp; path = ../../src/io/files/juce_TemporaryFile.cpp; sourceTree = SOURCE_ROOT; };
@@ -1713,6 +1714,7 @@
 				4EEF0B0BB4C3D1956B04122B,
 				59B2FFF817679AEA84375E1B,
 				49BF2B02A6D7B4438FC24839,
+				00B348FA35A7F691AEF84FBA,
 				D9B3C04F8EB4228DD59002E7,
 				42DA88264F768BAACD0414A3,
 				17C3AF03FF7AE88AE0C73311,

Juce.jucer

@@ -1177,6 +1177,8 @@
                 file="src/io/files/juce_FileSearchPath.cpp"/>
           <FILE id="YJYo7slcr" name="juce_FileSearchPath.h" compile="0" resource="0"
                 file="src/io/files/juce_FileSearchPath.h"/>
+          <FILE id="gPKPMY" name="juce_MemoryMappedFile.h" compile="0" resource="0"
+                file="src/io/files/juce_MemoryMappedFile.h"/>
           <FILE id="hwijIMGzE" name="juce_NamedPipe.cpp" compile="1" resource="0"
                 file="src/io/files/juce_NamedPipe.cpp"/>
           <FILE id="Jv4ugNwIx" name="juce_NamedPipe.h" compile="0" resource="0"

juce_amalgamated.cpp

@@ -773,6 +773,7 @@ protected:
 #include <sys/ptrace.h>
 #include <sys/vfs.h>
 #include <sys/wait.h>
+#include <sys/mman.h>
 #include <fnmatch.h>
 #include <utime.h>
 #include <pwd.h>
@@ -922,6 +923,7 @@ protected:
 #include <sys/param.h>
 #include <sys/mount.h>
 #include <sys/utsname.h>
+#include <sys/mman.h>
 #include <fnmatch.h>
 #include <utime.h>
 #include <dlfcn.h>
@@ -961,6 +963,7 @@ protected:
 #include <sys/statfs.h>
 #include <sys/ptrace.h>
 #include <sys/sysinfo.h>
+#include <sys/mman.h>
 #include <pwd.h>
 #include <dirent.h>
 #include <fnmatch.h>
@@ -7857,53 +7860,48 @@ bool File::isAbsolutePath (const String& path)
 const File File::getChildFile (String relativePath) const
 {
 	if (isAbsolutePath (relativePath))
-	{
-		// the path is really absolute..
 		return File (relativePath);
-	}
-	else
+
+	String path (fullPath);
+
+	// It's relative, so remove any ../ or ./ bits at the start..
+	if (relativePath[0] == '.')
 	{
-		// it's relative, so remove any ../ or ./ bits at the start.
-		String path (fullPath);
+	   #if JUCE_WINDOWS
+		relativePath = relativePath.replaceCharacter ('/', '\\').trimStart();
+	   #else
+		relativePath = relativePath.trimStart();
+	   #endif
 
-		if (relativePath[0] == '.')
+		while (relativePath[0] == '.')
 		{
-		   #if JUCE_WINDOWS
-			relativePath = relativePath.replaceCharacter ('/', '\\').trimStart();
-		   #else
-			relativePath = relativePath.trimStart();
-		   #endif
-
-			while (relativePath[0] == '.')
+			if (relativePath[1] == '.')
 			{
-				if (relativePath[1] == '.')
+				if (relativePath [2] == 0 || relativePath[2] == separator)
 				{
-					if (relativePath [2] == 0 || relativePath[2] == separator)
-					{
-						const int lastSlash = path.lastIndexOfChar (separator);
-						if (lastSlash >= 0)
-							path = path.substring (0, lastSlash);
+					const int lastSlash = path.lastIndexOfChar (separator);
+					if (lastSlash >= 0)
+						path = path.substring (0, lastSlash);
 
-						relativePath = relativePath.substring (3);
-					}
-					else
-					{
-						break;
-					}
-				}
-				else if (relativePath[1] == separator)
-				{
-					relativePath = relativePath.substring (2);
+					relativePath = relativePath.substring (3);
 				}
 				else
 				{
 					break;
 				}
 			}
+			else if (relativePath[1] == separator)
+			{
+				relativePath = relativePath.substring (2);
+			}
+			else
+			{
+				break;
+			}
 		}
-
-		return File (addTrailingSeparator (path) + relativePath);
 	}
+
+	return File (addTrailingSeparator (path) + relativePath);
 }
 
 const File File::getSiblingFile (const String& fileName) const
@@ -8481,6 +8479,39 @@ public:
 			expect (mb[0] == '0');
 		}
 
+		beginTest ("Memory-mapped files");
+
+		{
+			MemoryMappedFile mmf (tempFile, MemoryMappedFile::readOnly);
+			expect (mmf.getSize() == 10);
+			expect (mmf.getData() != nullptr);
+			expect (memcmp (mmf.getData(), "0123456789", 10) == 0);
+		}
+
+		{
+			const File tempFile2 (tempFile.getNonexistentSibling (false));
+			expect (tempFile2.create());
+			expect (tempFile2.appendData ("xxxxxxxxxx", 10));
+
+			{
+				MemoryMappedFile mmf (tempFile2, MemoryMappedFile::readWrite);
+				expect (mmf.getSize() == 10);
+				expect (mmf.getData() != nullptr);
+				memcpy (mmf.getData(), "abcdefghij", 10);
+			}
+
+			{
+				MemoryMappedFile mmf (tempFile2, MemoryMappedFile::readWrite);
+				expect (mmf.getSize() == 10);
+				expect (mmf.getData() != nullptr);
+				expect (memcmp (mmf.getData(), "abcdefghij", 10) == 0);
+			}
+
+			expect (tempFile2.deleteFile());
+		}
+
+		beginTest ("More writing");
+
 		expect (tempFile.appendData ("abcdefghij", 10));
 		expect (tempFile.getSize() == 20);
 		expect (tempFile.replaceWithData ("abcdefghij", 10));
@@ -244800,6 +244831,55 @@ void FileOutputStream::flushInternal()
 			status = WindowsFileHelpers::getResultForLastError();
 }
 
+MemoryMappedFile::MemoryMappedFile (const File& file, MemoryMappedFile::AccessMode mode)
+	: address (nullptr),
+	  internal (nullptr),
+	  length (0)
+{
+	jassert (mode == readOnly || mode == readWrite);
+
+	DWORD accessMode = GENERIC_READ, shareMode = FILE_SHARE_READ, createType = OPEN_EXISTING;
+	DWORD protect = PAGE_READONLY, access = FILE_MAP_READ;
+
+	if (mode == readWrite)
+	{
+		accessMode = GENERIC_READ | GENERIC_WRITE;
+		createType = OPEN_ALWAYS;
+		protect = PAGE_READWRITE;
+		access = FILE_MAP_ALL_ACCESS;
+	}
+
+	HANDLE h = CreateFile (file.getFullPathName().toWideCharPointer(), accessMode, FILE_SHARE_READ, 0,
+						   createType, FILE_ATTRIBUTE_NORMAL, 0);
+
+	internal = (void*) h;
+
+	if (h != INVALID_HANDLE_VALUE)
+	{
+		const int64 fileSize = file.getSize();
+
+		HANDLE mappingHandle = CreateFileMapping (h, 0, protect, (DWORD) (fileSize >> 32), (DWORD) fileSize, 0);
+		if (mappingHandle != 0)
+		{
+			address = MapViewOfFile (mappingHandle, access, 0, 0, (SIZE_T) fileSize);
+
+			if (address != nullptr)
+				length = (size_t) fileSize;
+
+			CloseHandle (mappingHandle);
+		}
+	}
+}
+
+MemoryMappedFile::~MemoryMappedFile()
+{
+	if (address != nullptr)
+		UnmapViewOfFile (address);
+
+	if (internal != nullptr)
+		CloseHandle ((HANDLE) internal);
+}
+
 int64 File::getSize() const
 {
 	WIN32_FILE_ATTRIBUTE_DATA attributes;
@@ -260588,6 +260668,46 @@ void FileOutputStream::flushInternal()
 			status = getResultForErrno();
 }
 
+MemoryMappedFile::MemoryMappedFile (const File& file, MemoryMappedFile::AccessMode mode)
+	: address (nullptr),
+	  internal (nullptr),
+	  length (0)
+{
+	jassert (mode == readOnly || mode == readWrite);
+
+	const int fd = open (file.getFullPathName().toUTF8(),
+						 mode == readWrite ? (O_CREAT + O_RDWR) : O_RDONLY, 00644);
+
+	internal = reinterpret_cast<void*> (fd);
+
+	if (fd != -1)
+	{
+		const int64 fileSize = file.getSize();
+
+		address = mmap (0, (size_t) fileSize,
+						mode == readWrite ? (PROT_READ | PROT_WRITE) : PROT_READ,
+						MAP_SHARED, fd, 0);
+
+		if (address == MAP_FAILED)
+			address = nullptr;
+		else
+			length = (size_t) fileSize;
+	}
+}
+
+MemoryMappedFile::~MemoryMappedFile()
+{
+	const int fd = reinterpret_cast <int> (internal);
+
+	if (fd != 0)
+	{
+		if (address != nullptr)
+			munmap (address, length);
+
+		close (fd);
+	}
+}
+
 const File juce_getExecutableFile()
 {
    #if JUCE_ANDROID
@@ -270579,6 +270699,46 @@ void FileOutputStream::flushInternal()
 			status = getResultForErrno();
 }
 
+MemoryMappedFile::MemoryMappedFile (const File& file, MemoryMappedFile::AccessMode mode)
+	: address (nullptr),
+	  internal (nullptr),
+	  length (0)
+{
+	jassert (mode == readOnly || mode == readWrite);
+
+	const int fd = open (file.getFullPathName().toUTF8(),
+						 mode == readWrite ? (O_CREAT + O_RDWR) : O_RDONLY, 00644);
+
+	internal = reinterpret_cast<void*> (fd);
+
+	if (fd != -1)
+	{
+		const int64 fileSize = file.getSize();
+
+		address = mmap (0, (size_t) fileSize,
+						mode == readWrite ? (PROT_READ | PROT_WRITE) : PROT_READ,
+						MAP_SHARED, fd, 0);
+
+		if (address == MAP_FAILED)
+			address = nullptr;
+		else
+			length = (size_t) fileSize;
+	}
+}
+
+MemoryMappedFile::~MemoryMappedFile()
+{
+	const int fd = reinterpret_cast <int> (internal);
+
+	if (fd != 0)
+	{
+		if (address != nullptr)
+			munmap (address, length);
+
+		close (fd);
+	}
+}
+
 const File juce_getExecutableFile()
 {
    #if JUCE_ANDROID
@@ -287465,6 +287625,46 @@ void FileOutputStream::flushInternal()
 			status = getResultForErrno();
 }
 
+MemoryMappedFile::MemoryMappedFile (const File& file, MemoryMappedFile::AccessMode mode)
+	: address (nullptr),
+	  internal (nullptr),
+	  length (0)
+{
+	jassert (mode == readOnly || mode == readWrite);
+
+	const int fd = open (file.getFullPathName().toUTF8(),
+						 mode == readWrite ? (O_CREAT + O_RDWR) : O_RDONLY, 00644);
+
+	internal = reinterpret_cast<void*> (fd);
+
+	if (fd != -1)
+	{
+		const int64 fileSize = file.getSize();
+
+		address = mmap (0, (size_t) fileSize,
+						mode == readWrite ? (PROT_READ | PROT_WRITE) : PROT_READ,
+						MAP_SHARED, fd, 0);
+
+		if (address == MAP_FAILED)
+			address = nullptr;
+		else
+			length = (size_t) fileSize;
+	}
+}
+
+MemoryMappedFile::~MemoryMappedFile()
+{
+	const int fd = reinterpret_cast <int> (internal);
+
+	if (fd != 0)
+	{
+		if (address != nullptr)
+			munmap (address, length);
+
+		close (fd);
+	}
+}
+
 const File juce_getExecutableFile()
 {
    #if JUCE_ANDROID

juce_amalgamated.h

@@ -73,7 +73,7 @@ namespace JuceDummyNamespace {}
 */
 #define JUCE_MAJOR_VERSION	  1
 #define JUCE_MINOR_VERSION	  53
-#define JUCE_BUILDNUMBER	88
+#define JUCE_BUILDNUMBER	89
 
 /** Current Juce version number.
 
@@ -19409,6 +19409,68 @@ private:
 /*** End of inlined file: juce_FileSearchPath.h ***/
 
 
+#endif
+#ifndef __JUCE_MEMORYMAPPEDFILE_JUCEHEADER__
+
+/*** Start of inlined file: juce_MemoryMappedFile.h ***/
+#ifndef __JUCE_MEMORYMAPPEDFILE_JUCEHEADER__
+#define __JUCE_MEMORYMAPPEDFILE_JUCEHEADER__
+
+/**
+	Maps a file into virtual memory for easy reading and/or writing.
+*/
+class JUCE_API  MemoryMappedFile
+{
+public:
+	/** The read/write flags used when opening a memory mapped file. */
+	enum AccessMode
+	{
+		readOnly,   /**< Indicates that the memory can only be read. */
+		readWrite   /**< Indicates that the memory can be read and written to - changes that are
+						 made will be flushed back to disk at the whim of the OS. */
+	};
+
+	/** Opens a file and maps it to an area of virtual memory.
+
+		The file should already exist, and should already be the size that you want to work with
+		when you call this. If the file is resized after being opened, the behaviour is undefined.
+
+		If the file exists and the operation succeeds, the getData() and getSize() methods will
+		return the location and size of the data that can be read or written. Note that the entire
+		file is not read into memory immediately - the OS simply creates a virtual mapping, which
+		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.
+	*/
+	MemoryMappedFile (const File& file, AccessMode mode);
+
+	/** Destructor. */
+	~MemoryMappedFile();
+
+	/** Returns the address at which this file has been mapped, or a null pointer if
+		the file couldn't be successfully mapped.
+	*/
+	void* getData() const noexcept		  { return address; }
+
+	/** Returns the number of bytes of data that are available for reading or writing.
+		This will normally be the size of the file.
+	*/
+	size_t getSize() const noexcept		 { return length; }
+
+private:
+
+	void* address;
+	void* internal;
+	size_t length;
+
+	JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (MemoryMappedFile);
+};
+
+#endif   // __JUCE_MEMORYMAPPEDFILE_JUCEHEADER__
+
+/*** End of inlined file: juce_MemoryMappedFile.h ***/
+
+
 #endif
 #ifndef __JUCE_NAMEDPIPE_JUCEHEADER__
 

src/core/juce_StandardHeader.h

@@ -33,7 +33,7 @@
 */
 #define JUCE_MAJOR_VERSION      1
 #define JUCE_MINOR_VERSION      53
-#define JUCE_BUILDNUMBER        88
+#define JUCE_BUILDNUMBER        89
 
 /** Current Juce version number.
 

src/io/files/juce_File.cpp

@@ -380,53 +380,48 @@ bool File::isAbsolutePath (const String& path)
 const File File::getChildFile (String relativePath) const
 {
     if (isAbsolutePath (relativePath))
-    {
-        // the path is really absolute..
         return File (relativePath);
-    }
-    else
+
+    String path (fullPath);
+
+    // It's relative, so remove any ../ or ./ bits at the start..
+    if (relativePath[0] == '.')
     {
-        // it's relative, so remove any ../ or ./ bits at the start.
-        String path (fullPath);
+       #if JUCE_WINDOWS
+        relativePath = relativePath.replaceCharacter ('/', '\\').trimStart();
+       #else
+        relativePath = relativePath.trimStart();
+       #endif
 
-        if (relativePath[0] == '.')
+        while (relativePath[0] == '.')
         {
-           #if JUCE_WINDOWS
-            relativePath = relativePath.replaceCharacter ('/', '\\').trimStart();
-           #else
-            relativePath = relativePath.trimStart();
-           #endif
-
-            while (relativePath[0] == '.')
+            if (relativePath[1] == '.')
             {
-                if (relativePath[1] == '.')
+                if (relativePath [2] == 0 || relativePath[2] == separator)
                 {
-                    if (relativePath [2] == 0 || relativePath[2] == separator)
-                    {
-                        const int lastSlash = path.lastIndexOfChar (separator);
-                        if (lastSlash >= 0)
-                            path = path.substring (0, lastSlash);
-
-                        relativePath = relativePath.substring (3);
-                    }
-                    else
-                    {
-                        break;
-                    }
-                }
-                else if (relativePath[1] == separator)
-                {
-                    relativePath = relativePath.substring (2);
+                    const int lastSlash = path.lastIndexOfChar (separator);
+                    if (lastSlash >= 0)
+                        path = path.substring (0, lastSlash);
+
+                    relativePath = relativePath.substring (3);
                 }
                 else
                 {
                     break;
                 }
             }
+            else if (relativePath[1] == separator)
+            {
+                relativePath = relativePath.substring (2);
+            }
+            else
+            {
+                break;
+            }
         }
-
-        return File (addTrailingSeparator (path) + relativePath);
     }
+
+    return File (addTrailingSeparator (path) + relativePath);
 }
 
 const File File::getSiblingFile (const String& fileName) const
@@ -904,6 +899,8 @@ const File File::createTempFile (const String& fileNameEnding)
 
 #include "../../utilities/juce_UnitTest.h"
 #include "../../maths/juce_Random.h"
+#include "juce_MemoryMappedFile.h"
+
 
 class FileTests  : public UnitTest
 {
@@ -1022,6 +1019,39 @@ public:
             expect (mb[0] == '0');
         }
 
+        beginTest ("Memory-mapped files");
+
+        {
+            MemoryMappedFile mmf (tempFile, MemoryMappedFile::readOnly);
+            expect (mmf.getSize() == 10);
+            expect (mmf.getData() != nullptr);
+            expect (memcmp (mmf.getData(), "0123456789", 10) == 0);
+        }
+
+        {
+            const File tempFile2 (tempFile.getNonexistentSibling (false));
+            expect (tempFile2.create());
+            expect (tempFile2.appendData ("xxxxxxxxxx", 10));
+
+            {
+                MemoryMappedFile mmf (tempFile2, MemoryMappedFile::readWrite);
+                expect (mmf.getSize() == 10);
+                expect (mmf.getData() != nullptr);
+                memcpy (mmf.getData(), "abcdefghij", 10);
+            }
+
+            {
+                MemoryMappedFile mmf (tempFile2, MemoryMappedFile::readWrite);
+                expect (mmf.getSize() == 10);
+                expect (mmf.getData() != nullptr);
+                expect (memcmp (mmf.getData(), "abcdefghij", 10) == 0);
+            }
+
+            expect (tempFile2.deleteFile());
+        }
+
+        beginTest ("More writing");
+
         expect (tempFile.appendData ("abcdefghij", 10));
         expect (tempFile.getSize() == 20);
         expect (tempFile.replaceWithData ("abcdefghij", 10));

src/io/files/juce_MemoryMappedFile.h

@@ -0,0 +1,84 @@
+/*
+  ==============================================================================
+
+   This file is part of the JUCE library - "Jules' Utility Class Extensions"
+   Copyright 2004-11 by Raw Material Software Ltd.
+
+  ------------------------------------------------------------------------------
+
+   JUCE can be redistributed and/or modified under the terms of the GNU General
+   Public License (Version 2), as published by the Free Software Foundation.
+   A copy of the license is included in the JUCE distribution, or can be found
+   online at www.gnu.org/licenses.
+
+   JUCE is distributed in the hope that it will be useful, but WITHOUT ANY
+   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+   A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  ------------------------------------------------------------------------------
+
+   To release a closed-source product which uses JUCE, commercial licenses are
+   available: visit www.rawmaterialsoftware.com/juce for more information.
+
+  ==============================================================================
+*/
+
+#ifndef __JUCE_MEMORYMAPPEDFILE_JUCEHEADER__
+#define __JUCE_MEMORYMAPPEDFILE_JUCEHEADER__
+
+#include "juce_File.h"
+
+//==============================================================================
+/**
+    Maps a file into virtual memory for easy reading and/or writing.
+*/
+class JUCE_API  MemoryMappedFile
+{
+public:
+    /** The read/write flags used when opening a memory mapped file. */
+    enum AccessMode
+    {
+        readOnly,   /**< Indicates that the memory can only be read. */
+        readWrite   /**< Indicates that the memory can be read and written to - changes that are
+                         made will be flushed back to disk at the whim of the OS. */
+    };
+
+    /** Opens a file and maps it to an area of virtual memory.
+
+        The file should already exist, and should already be the size that you want to work with
+        when you call this. If the file is resized after being opened, the behaviour is undefined.
+
+        If the file exists and the operation succeeds, the getData() and getSize() methods will
+        return the location and size of the data that can be read or written. Note that the entire
+        file is not read into memory immediately - the OS simply creates a virtual mapping, which
+        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.
+    */
+    MemoryMappedFile (const File& file, AccessMode mode);
+
+    /** Destructor. */
+    ~MemoryMappedFile();
+
+    /** Returns the address at which this file has been mapped, or a null pointer if
+        the file couldn't be successfully mapped.
+    */
+    void* getData() const noexcept              { return address; }
+
+    /** Returns the number of bytes of data that are available for reading or writing.
+        This will normally be the size of the file.
+    */
+    size_t getSize() const noexcept             { return length; }
+
+
+private:
+    //==============================================================================
+    void* address;
+    void* internal;
+    size_t length;
+
+    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (MemoryMappedFile);
+};
+
+
+#endif   // __JUCE_MEMORYMAPPEDFILE_JUCEHEADER__

src/juce_core_includes.h

@@ -146,6 +146,9 @@
 #ifndef __JUCE_FILESEARCHPATH_JUCEHEADER__
  #include "io/files/juce_FileSearchPath.h"
 #endif
+#ifndef __JUCE_MEMORYMAPPEDFILE_JUCEHEADER__
+ #include "io/files/juce_MemoryMappedFile.h"
+#endif
 #ifndef __JUCE_NAMEDPIPE_JUCEHEADER__
  #include "io/files/juce_NamedPipe.h"
 #endif

src/native/android/juce_android_NativeCode.cpp

@@ -53,6 +53,7 @@ BEGIN_JUCE_NAMESPACE
 #include "../../io/files/juce_FileOutputStream.h"
 #include "../../io/files/juce_NamedPipe.h"
 #include "../../io/files/juce_DirectoryIterator.h"
+#include "../../io/files/juce_MemoryMappedFile.h"
 #include "../../io/network/juce_URL.h"
 #include "../../io/network/juce_MACAddress.h"
 #include "../../core/juce_PlatformUtilities.h"

src/native/android/juce_android_NativeIncludes.h

@@ -43,6 +43,7 @@
 #include <sys/statfs.h>
 #include <sys/ptrace.h>
 #include <sys/sysinfo.h>
+#include <sys/mman.h>
 #include <pwd.h>
 #include <dirent.h>
 #include <fnmatch.h>

src/native/common/juce_posix_SharedCode.h

@@ -523,6 +523,47 @@ void FileOutputStream::flushInternal()
             status = getResultForErrno();
 }
 
+//==============================================================================
+MemoryMappedFile::MemoryMappedFile (const File& file, MemoryMappedFile::AccessMode mode)
+    : address (nullptr),
+      internal (nullptr),
+      length (0)
+{
+    jassert (mode == readOnly || mode == readWrite);
+
+    const int fd = open (file.getFullPathName().toUTF8(),
+                         mode == readWrite ? (O_CREAT + O_RDWR) : O_RDONLY, 00644);
+
+    internal = reinterpret_cast<void*> (fd);
+
+    if (fd != -1)
+    {
+        const int64 fileSize = file.getSize();
+
+        address = mmap (0, (size_t) fileSize,
+                        mode == readWrite ? (PROT_READ | PROT_WRITE) : PROT_READ,
+                        MAP_SHARED, fd, 0);
+
+        if (address == MAP_FAILED)
+            address = nullptr;
+        else
+            length = (size_t) fileSize;
+    }
+}
+
+MemoryMappedFile::~MemoryMappedFile()
+{
+    const int fd = reinterpret_cast <int> (internal);
+
+    if (fd != 0)
+    {
+        if (address != nullptr)
+            munmap (address, length);
+
+        close (fd);
+    }
+}
+
 //==============================================================================
 const File juce_getExecutableFile()
 {

src/native/linux/juce_linux_NativeCode.cpp

@@ -64,6 +64,7 @@ BEGIN_JUCE_NAMESPACE
 #include "../../io/files/juce_FileInputStream.h"
 #include "../../io/files/juce_FileOutputStream.h"
 #include "../../io/files/juce_DirectoryIterator.h"
+#include "../../io/files/juce_MemoryMappedFile.h"
 #include "../../io/network/juce_URL.h"
 #include "../../io/network/juce_MACAddress.h"
 #include "../../io/streams/juce_MemoryInputStream.h"

src/native/linux/juce_linux_NativeIncludes.h

@@ -42,6 +42,7 @@
 #include <sys/ptrace.h>
 #include <sys/vfs.h>
 #include <sys/wait.h>
+#include <sys/mman.h>
 #include <fnmatch.h>
 #include <utime.h>
 #include <pwd.h>

src/native/mac/juce_mac_NativeCode.mm

@@ -53,6 +53,7 @@ BEGIN_JUCE_NAMESPACE
 #include "../../io/files/juce_FileOutputStream.h"
 #include "../../io/files/juce_NamedPipe.h"
 #include "../../io/files/juce_DirectoryIterator.h"
+#include "../../io/files/juce_MemoryMappedFile.h"
 #include "../../io/network/juce_URL.h"
 #include "../../io/network/juce_MACAddress.h"
 #include "../../io/streams/juce_MemoryInputStream.h"

src/native/mac/juce_mac_NativeIncludes.h

@@ -70,6 +70,7 @@
 #include <sys/param.h>
 #include <sys/mount.h>
 #include <sys/utsname.h>
+#include <sys/mman.h>
 #include <fnmatch.h>
 #include <utime.h>
 #include <dlfcn.h>

src/native/windows/juce_win32_Files.cpp

@@ -299,6 +299,56 @@ void FileOutputStream::flushInternal()
             status = WindowsFileHelpers::getResultForLastError();
 }
 
+//==============================================================================
+MemoryMappedFile::MemoryMappedFile (const File& file, MemoryMappedFile::AccessMode mode)
+    : address (nullptr),
+      internal (nullptr),
+      length (0)
+{
+    jassert (mode == readOnly || mode == readWrite);
+
+    DWORD accessMode = GENERIC_READ, shareMode = FILE_SHARE_READ, createType = OPEN_EXISTING;
+    DWORD protect = PAGE_READONLY, access = FILE_MAP_READ;
+
+    if (mode == readWrite)
+    {
+        accessMode = GENERIC_READ | GENERIC_WRITE;
+        createType = OPEN_ALWAYS;
+        protect = PAGE_READWRITE;
+        access = FILE_MAP_ALL_ACCESS;
+    }
+
+    HANDLE h = CreateFile (file.getFullPathName().toWideCharPointer(), accessMode, FILE_SHARE_READ, 0,
+                           createType, FILE_ATTRIBUTE_NORMAL, 0);
+
+    internal = (void*) h;
+
+    if (h != INVALID_HANDLE_VALUE)
+    {
+        const int64 fileSize = file.getSize();
+
+        HANDLE mappingHandle = CreateFileMapping (h, 0, protect, (DWORD) (fileSize >> 32), (DWORD) fileSize, 0);
+        if (mappingHandle != 0)
+        {
+            address = MapViewOfFile (mappingHandle, access, 0, 0, (SIZE_T) fileSize);
+
+            if (address != nullptr)
+                length = (size_t) fileSize;
+
+            CloseHandle (mappingHandle);
+        }
+    }
+}
+
+MemoryMappedFile::~MemoryMappedFile()
+{
+    if (address != nullptr)
+        UnmapViewOfFile (address);
+
+    if (internal != nullptr)
+        CloseHandle ((HANDLE) internal);
+}
+
 //==============================================================================
 int64 File::getSize() const
 {

src/native/windows/juce_win32_NativeCode.cpp

@@ -54,6 +54,7 @@ BEGIN_JUCE_NAMESPACE
 #include "../../io/streams/juce_MemoryOutputStream.h"
 #include "../../io/files/juce_NamedPipe.h"
 #include "../../io/files/juce_DirectoryIterator.h"
+#include "../../io/files/juce_MemoryMappedFile.h"
 #include "../../io/network/juce_URL.h"
 #include "../../io/network/juce_MACAddress.h"
 #include "../../core/juce_PlatformUtilities.h"