SharedMemory

CREATOR

public static final Creator<SharedMemory> CREATOR

close

public void close ()

Close the backing FileDescriptor of this SharedMemory instance. Note that all open mappings of the shared memory will remain valid and may continue to be used. The shared memory will not be freed until all file descriptor handles are closed and all memory mappings are unmapped.

create

public static SharedMemory create (String name, 
                int size)

Creates an anonymous SharedMemory instance with the provided debug name and size. The name is only used for debugging purposes and can help identify what the shared memory is used for when inspecting memory maps for the processes that have mapped this SharedMemory instance.

describeContents

public int describeContents ()

Describe the kinds of special objects contained in this Parcelable instance's marshaled representation. For example, if the object will include a file descriptor in the output of writeToParcel(android.os.Parcel, int), the return value of this method must include the CONTENTS_FILE_DESCRIPTOR bit.

fromFileDescriptor

public static SharedMemory fromFileDescriptor (ParcelFileDescriptor fd)

Creates an instance from existing shared memory passed as ParcelFileDescriptor.

The fd should be a shared memory created from SharedMemory or ASharedMemory. This can be useful when shared memory is passed as file descriptor through JNI or binder service implemented in cpp.

Note that newly created SharedMemory takes ownership of passed fd and the original fd becomes detached (Check ParcelFileDescriptor.detachFd()). If the caller wants to use the file descriptor after the call, the caller should duplicate the file descriptor (Check ParcelFileDescriptor.dup()) and pass the duped version instead.

getSize

public int getSize ()

map

public ByteBuffer map (int prot, 
                int offset, 
                int length)

Creates an mmap of the SharedMemory with the specified prot, offset, and length. This will always produce a new ByteBuffer window to the backing shared memory region. Every call to map() may be paired with a call to unmap(java.nio.ByteBuffer) when the ByteBuffer returned by map() is no longer needed.

mapReadOnly

public ByteBuffer mapReadOnly ()

Creates a read-only mapping of the entire shared memory region. This requires the the protection level of the shared memory is at least PROT_READ or the map will fail. Use map(int, int, int) to have more control over the mapping if desired. This is equivalent to map(OsConstants.PROT_READ, 0, getSize())

mapReadWrite

public ByteBuffer mapReadWrite ()

Creates a read/write mapping of the entire shared memory region. This requires the the protection level of the shared memory is at least PROT_READ|PROT_WRITE or the map will fail. Use map(int, int, int) to have more control over the mapping if desired. This is equivalent to map(OsConstants.PROT_READ | OsConstants.PROT_WRITE, 0, getSize())

setProtect

public boolean setProtect (int prot)

Sets the protection on the shared memory to the combination specified in prot, which is either a bitwise-or'd combination of OsConstants.PROT_READ, OsConstants.PROT_WRITE, OsConstants.PROT_EXEC from OsConstants, or OsConstants.PROT_NONE, to remove all further access. Note that protection can only ever be removed, not added. By default shared memory is created with protection set to PROT_READ | PROT_WRITE | PROT_EXEC. The protection passed here also only applies to any mappings created after calling this method. Existing mmaps of the shared memory retain whatever protection they had when they were created. A common usage of this is to share a read-only copy of the data with something else. To do that first create the read/write mapping with PROT_READ | PROT_WRITE, then call setProtect(PROT_READ) to remove write capability, then send the SharedMemory to another process. That process will only be able to mmap with PROT_READ.

unmap

public static void unmap (ByteBuffer buffer)

Unmaps a buffer previously returned by map(int, int, int). This will immediately release the backing memory of the ByteBuffer, invalidating all references to it. Only call this method if there are no duplicates of the ByteBuffer in use and don't access the ByteBuffer after calling this method.

writeToParcel

public void writeToParcel (Parcel dest, 
                int flags)

Flatten this object in to a Parcel.