FLUSH(5) FLUSH(5)
NAME
flush - abort a message
SYNOPSIS
size[4] Tflush tag[2] oldtag[2]
size[4] Rflush tag[2]
DESCRIPTION
When the response to a request is no longer needed, such as
when a user interrupts a process doing a sys-read(2), a
Tflush request is sent to the server to purge the pending
response. The message being flushed is identified by
oldtag. The semantics of flush depends on messages arriving
in order.
The server must answer the flush message immediately. If it
recognizes oldtag as the tag of a pending transaction, it
should abort any pending response and discard that tag. In
either case, it should respond with an Rflush echoing the
tag (not oldtag) of the Tflush message. A Tflush can never
be responded to by an Rerror message.
When the client sends a Tflush, it must wait to receive the
corresponding Rflush before reusing oldtag for subsequent
messages. If a response to the flushed request is received
before the Rflush, the client must honor the response as if
it had not been flushed, since the completed request may
signify a state change in the server. For instance, Tcreate
may have created a file and Twalk may have allocated a fid.
If no response is received before the Rflush, the flushed
transaction is considered to have been cancelled, and should
be treated as though it had never been sent.
Several exceptional conditions are handled correctly by the
above specification: sending multiple flushes for a single
tag, flushing after a transaction is completed, flushing a
Tflush, and flushing an invalid tag.
SEE ALSO
sys-read(2).
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