SharedMemory
class SharedMemory : Closeable, Parcelable
SharedMemory enables the creation, mapping, and protection control over anonymous shared memory.
Summary
| Inherited constants |
From class Parcelable
Int |
CONTENTS_FILE_DESCRIPTOR
Descriptor bit used with describeContents(): indicates that the Parcelable object's flattened representation includes a file descriptor.
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Int |
PARCELABLE_WRITE_RETURN_VALUE
Flag for use with writeToParcel: the object being written is a return value, that is the result of a function such as "Parcelable someFunction()", "void someFunction(out Parcelable)", or "void someFunction(inout Parcelable)". Some implementations may want to release resources at this point.
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Public methods
close
fun close(): Unit
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.
| Exceptions |
java.lang.Exception |
if this resource cannot be closed |
java.io.IOException |
if an I/O error occurs |
create
static fun create(
name: String?,
size: Int
): SharedMemory
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.
| Parameters |
name |
String?: The debug name to use for this SharedMemory instance. This can be null, however a debug name is recommended to help identify memory usage when using tools such as lsof or examining /proc/[pid]/maps |
size |
Int: The size of the shared memory to create. Must be greater than 0. |
| Return |
SharedMemory |
A SharedMemory instance of the requested size This value cannot be null. |
| Exceptions |
android.system.ErrnoException |
if the requested allocation fails. |
describeContents
fun describeContents(): Int
fromFileDescriptor
static fun fromFileDescriptor(fd: ParcelFileDescriptor): SharedMemory
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
fun getSize(): Int
| Return |
Int |
The size of the SharedMemory region. |
map
fun map(
prot: Int,
offset: Int,
length: Int
): ByteBuffer
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.
| Parameters |
prot |
Int: A bitwise-or'd combination of PROT_READ, PROT_WRITE, PROT_EXEC, or PROT_NONE. |
offset |
Int: The offset into the shared memory to begin mapping. Must be >= 0 and less than getSize(). |
length |
Int: The length of the region to map. Must be > 0 and offset + length must not exceed getSize(). |
| Return |
ByteBuffer |
A ByteBuffer mapping. This value cannot be null. |
| Exceptions |
android.system.ErrnoException |
if the mmap call failed. |
mapReadOnly
fun mapReadOnly(): ByteBuffer
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())
| Return |
ByteBuffer |
A ByteBuffer mapping This value cannot be null. |
| Exceptions |
android.system.ErrnoException |
if the mmap call failed. |
mapReadWrite
fun mapReadWrite(): ByteBuffer
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())
| Return |
ByteBuffer |
A ByteBuffer mapping This value cannot be null. |
| Exceptions |
android.system.ErrnoException |
if the mmap call failed. |
setProtect
fun setProtect(prot: Int): Boolean
Sets the protection on the shared memory to the combination specified in prot, which is either a bitwise-or'd combination of android.system.OsConstants#PROT_READ, android.system.OsConstants#PROT_WRITE, android.system.OsConstants#PROT_EXEC from android.system.OsConstants, or android.system.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.
| Return |
Boolean |
Whether or not the requested protection was applied. Returns true on success, false if the requested protection was broader than the existing protection. |
unmap
static fun unmap(buffer: ByteBuffer): Unit
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.
| Parameters |
buffer |
ByteBuffer: The buffer to unmap This value cannot be null. |
writeToParcel
fun writeToParcel(
dest: Parcel,
flags: Int
): Unit
Flatten this object in to a Parcel.
Properties
