A file of another app that is kept readable by holding its descriptor open. More...

Inheritance diagram for de.yaacc.share.HeldFileSource:

Collaboration diagram for de.yaacc.share.HeldFileSource:

Classes
class	NotSeekableException
	The descriptor does not support positional reads (pipe, socket, device, not a regular file).

Static Public Member Functions
static boolean	isSeekable (FileDescriptor fd)
	Whether positional reads work on the descriptor: a regular file (`fstat`) on which `lseek(SEEK_CUR)` succeeds (it fails with ESPIPE for pipes and sockets).

static HeldFileSource	open (AssetFileDescriptor afd) throws IOException
	Holds the file behind the provider's descriptor.

Protected Member Functions
int	readAtInternal (long position, byte[] buf, int off, int len) throws IOException
	Reads from the backend.

void	closeInternal ()
	Closes the backend.

Protected Member Functions inherited from de.yaacc.share.PositionalSource
	PositionalSource (long size)

Additional Inherited Members
Public Member Functions inherited from de.yaacc.share.PositionalSource
final long	size ()

final int	readAt (long position, byte[] buf, int off, int len) throws IOException
	Reads up to `len` bytes starting at `position`.

final boolean	isClosing ()

final void	close ()
	Refuses new reads and closes the backend: now if nothing is reading, else when the last running read ends.

Detailed Description

A file of another app that is kept readable by holding its descriptor open.

The registry (as an AutoCloseable target of a LOCAL_FILE entry) closes it; closing never blocks and never happens while a read runs (PositionalSource).

Reads use Os#pread, which does not touch the file offset, so any number of responses read different ranges of the one descriptor. The held descriptor is a dup of the provider's one, and the provider's is closed, so the provider process is not pinned by a stable reference. The start offset and length the provider declares are clamped to the real file size (clampLength).

Member Function Documentation

◆ closeInternal()

void de.yaacc.share.HeldFileSource.closeInternal ( )

protected

Closes the backend.

Called exactly once, never while a read is running, possibly on a reader's thread. Should not throw; an exception is swallowed.

Reimplemented from de.yaacc.share.PositionalSource.

◆ isSeekable()

static boolean de.yaacc.share.HeldFileSource.isSeekable ( FileDescriptor fd )

static

Whether positional reads work on the descriptor: a regular file (fstat) on which lseek(SEEK_CUR) succeeds (it fails with ESPIPE for pipes and sockets).

Cheap and does not change the descriptor.

Returns: false for anything else, also when the check itself fails

Referenced by de.yaacc.share.HeldFileSource.open().

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◆ open()

static HeldFileSource de.yaacc.share.HeldFileSource.open ( AssetFileDescriptor afd ) throws IOException

static

Holds the file behind the provider's descriptor.

On success this method has duplicated the descriptor and closed afd, so the caller must not use or close it any more. On any failure afd is left open, untouched and still owned by the caller (who may then fall back to copying from it, and closes it).

Do not call on the main thread: fstat on a provider descriptor can block.

Exceptions

NotSeekableException	if the descriptor cannot be read positionally
IOException	if the descriptor is unusable (empty window, offset beyond the end, dup failed)

Referenced by de.yaacc.share.SharedFileOpener.openDescriptor().

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◆ readAtInternal()

int de.yaacc.share.HeldFileSource.readAtInternal	(	long	position,
		byte[]	buf,
		int	off,
		int	len ) throws IOException

protected

Reads from the backend.

Called with 0 <= position < size(), len > 0 and a valid buffer range; possibly from several threads at once; never after the backend was closed. May return fewer bytes than asked. Returns -1 (or 0) if the backend has no more data at that position.

Reimplemented from de.yaacc.share.PositionalSource.

The documentation for this class was generated from the following file:

/github/workspace/yaacc/src/main/java/de/yaacc/share/HeldFileSource.java

Classes

Static Public Member Functions