PollableOutputStream

Added in version 2.28.

class PollableOutputStream(*args, **kwargs)

Implementations: ConverterOutputStream, MemoryOutputStream, UnixOutputStream

GPollableOutputStream is implemented by OutputStream’s that can be polled for readiness to write. This can be used when interfacing with a non-GIO API that expects UNIX-file-descriptor-style asynchronous I/O rather than GIO-style.

Some classes may implement GPollableOutputStream but have only certain instances of that class be pollable. If can_poll returns false, then the behavior of other GPollableOutputStream methods is undefined.

Methods

class PollableOutputStream
can_poll() → bool

Checks if stream is actually pollable. Some classes may implement PollableOutputStream but have only certain instances of that class be pollable. If this method returns False, then the behavior of other PollableOutputStream methods is undefined.

For any given stream, the value returned by this method is constant; a stream cannot switch from pollable to non-pollable or vice versa.

Added in version 2.28.

create_source(cancellable: Cancellable | None = None) → Source

Creates a Source that triggers when stream can be written, or cancellable is triggered or an error occurs. The callback on the source is of the GPollableSourceFunc type.

As with is_writable(), it is possible that the stream may not actually be writable even after the source triggers, so you should use write_nonblocking() rather than write() from the callback.

The behaviour of this method is undefined if can_poll() returns False for stream.

Added in version 2.28.

Parameters:

cancellable – a Cancellable, or None

is_writable() → bool

Checks if stream can be written.

Note that some stream types may not be able to implement this 100% reliably, and it is possible that a call to write() after this returns True would still block. To guarantee non-blocking behavior, you should always use write_nonblocking(), which will return a WOULD_BLOCK error rather than blocking.

The behaviour of this method is undefined if can_poll() returns False for stream.

Added in version 2.28.

write_nonblocking(buffer: Sequence[int], cancellable: Cancellable | None = None) → int

Attempts to write up to count bytes from buffer to stream, as with write(). If stream is not currently writable, this will immediately return WOULD_BLOCK, and you can use create_source() to create a Source that will be triggered when stream is writable.

Note that since this method never blocks, you cannot actually use cancellable to cancel it. However, it will return an error if cancellable has already been cancelled when you call, which may happen if you call this method after a source triggers due to having been cancelled.

Also note that if WOULD_BLOCK is returned some underlying transports like D/TLS require that you re-send the same buffer and count in the next write call.

The behaviour of this method is undefined if can_poll() returns False for stream.

Parameters:

  • buffer – a buffer to write data from

  • cancellable – a Cancellable, or None

writev_nonblocking(vectors: Sequence[OutputVector], cancellable: Cancellable | None = None) → tuple[PollableReturn, int]

Attempts to write the bytes contained in the n_vectors vectors to stream, as with writev(). If stream is not currently writable, this will immediately return %``G_POLLABLE_RETURN_WOULD_BLOCK``, and you can use create_source() to create a Source that will be triggered when stream is writable. error will not be set in that case.

Note that since this method never blocks, you cannot actually use cancellable to cancel it. However, it will return an error if cancellable has already been cancelled when you call, which may happen if you call this method after a source triggers due to having been cancelled.

Also note that if WOULD_BLOCK is returned some underlying transports like D/TLS require that you re-send the same vectors and n_vectors in the next write call.

The behaviour of this method is undefined if can_poll() returns False for stream.

Added in version 2.60.

Parameters:

Virtual Methods

class PollableOutputStream
do_can_poll() → bool

Checks if stream is actually pollable. Some classes may implement PollableOutputStream but have only certain instances of that class be pollable. If this method returns False, then the behavior of other PollableOutputStream methods is undefined.

For any given stream, the value returned by this method is constant; a stream cannot switch from pollable to non-pollable or vice versa.

Added in version 2.28.

do_create_source(cancellable: Cancellable | None = None) → Source

Creates a Source that triggers when stream can be written, or cancellable is triggered or an error occurs. The callback on the source is of the GPollableSourceFunc type.

As with is_writable(), it is possible that the stream may not actually be writable even after the source triggers, so you should use write_nonblocking() rather than write() from the callback.

The behaviour of this method is undefined if can_poll() returns False for stream.

Added in version 2.28.

Parameters:

cancellable – a Cancellable, or None

do_is_writable() → bool

Checks if stream can be written.

Note that some stream types may not be able to implement this 100% reliably, and it is possible that a call to write() after this returns True would still block. To guarantee non-blocking behavior, you should always use write_nonblocking(), which will return a WOULD_BLOCK error rather than blocking.

The behaviour of this method is undefined if can_poll() returns False for stream.

Added in version 2.28.

do_write_nonblocking(buffer: Sequence[int] | None = None) → int

Attempts to write up to count bytes from buffer to stream, as with write(). If stream is not currently writable, this will immediately return WOULD_BLOCK, and you can use create_source() to create a Source that will be triggered when stream is writable.

Note that since this method never blocks, you cannot actually use cancellable to cancel it. However, it will return an error if cancellable has already been cancelled when you call, which may happen if you call this method after a source triggers due to having been cancelled.

Also note that if WOULD_BLOCK is returned some underlying transports like D/TLS require that you re-send the same buffer and count in the next write call.

The behaviour of this method is undefined if can_poll() returns False for stream.

Parameters:

buffer – a buffer to write data from

do_writev_nonblocking(vectors: Sequence[OutputVector]) → tuple[PollableReturn, int]

Attempts to write the bytes contained in the n_vectors vectors to stream, as with writev(). If stream is not currently writable, this will immediately return %``G_POLLABLE_RETURN_WOULD_BLOCK``, and you can use create_source() to create a Source that will be triggered when stream is writable. error will not be set in that case.

Note that since this method never blocks, you cannot actually use cancellable to cancel it. However, it will return an error if cancellable has already been cancelled when you call, which may happen if you call this method after a source triggers due to having been cancelled.

Also note that if WOULD_BLOCK is returned some underlying transports like D/TLS require that you re-send the same vectors and n_vectors in the next write call.

The behaviour of this method is undefined if can_poll() returns False for stream.

Added in version 2.60.

Parameters:

vectors – the buffer containing the OutputVector to write.