Struct reopen::Reopen [−][src]
pub struct Reopen<FD> { /* fields omitted */ }
Expand description
A Read
/Write
proxy that can reopen the underlying object.
It is constructed with a function that can open a new instance of the object. If it is signaled
to reopen it (though handle
), it drops the old instance and uses the
function to create a new one at the next IO operation.
Error handling
The reopening is performed lazily, on the first operation done to the object. Opening a new
instance can fail with an error. If this happens, the error is returned as part of the
operation being performed ‒ therefore, you can get an error like File not found
while
performing read
.
If an error happens, the operation is aborted. Next time an operation is performed, another attempt to open the object is made (which in turn can fail again).
Scheduling of a reopen
The implementation tries to ensure whole operations happen on the same FD. For example, even if
multiple read
calls need to be performed as part of
read_exact
, the Reopen
will check for reopening flags only once
before the whole operation and then will keep the same FD.
If this is not enough, the Reopen
can be locked to bundle multiple
operations without reopening.
Handling of ends
Certain operations make ordinary file descriptors „finished“ ‒ for example,
read_to_end
. Usually, further calls to any read operations would produce
EOF from then on.
While this reaches the end of the currently opened FD and further read operations would still
produce EOF, reopening the FD may lead to it being readable again. Therefore, reaching EOF is
not necessarily final for Reopen
.
Implementations
Creates a new instance.
Creates a new instance from the given handle.
This might come useful if you want to create the handle beforehand with
Handle::stub
(eg. in
once_cell
).
Note that using the same handle for multiple Reopen
s will not work as expected (the first
one to be used resets the signal and the others don’t reopen).
Examples
// Something that implements `Write`, for example.
struct Writer;
let handle = Handle::stub();
let reopen = Reopen::with_handle(handle.clone(), Box::new(|| Ok(Writer)));
handle.reopen();
Lock the Reopen
against reopening in the middle of operation.
In case of needing to perform multiple operations without reopening in the middle, it can be locked by this method. This provides access to the inner FD.
Errors
This can result in an error in case the FD needs to be reopened (or wasn’t opened previously) and the reopening results in an error.
Examples
let mut writer = Reopen::new(Box::new(|| {
// Vec::<u8> is an in-memory writer
Ok(Vec::new())
}))?;
let handle = writer.handle();
let mut lock = writer.lock()?;
write!(&mut lock, "Hello ")?;
// Request reopening. But as we locked, it won't happen until we are done with it.
handle.reopen();
write!(&mut lock, "world")?;
// See? Both writes are here now.
assert_eq!(b"Hello world", &lock[..]);
// But when we return to using the writer directly (and drop the lock by that), it gets
// reopened and we get a whole new Vec to play with.
write!(&mut writer, "Another message")?;
assert_eq!(b"Another message", &writer.lock()?[..]);
Trait Implementations
Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more
Read the exact number of bytes required to fill buf
. Read more
Read all bytes until EOF in this source, placing them into buf
. Read more
Read all bytes until EOF in this source, appending them to buf
. Read more
Like read
, except that it reads into a slice of buffers. Read more
can_vector
)Determines if this Read
er has an efficient read_vectored
implementation. Read more
read_initializer
)Determines if this Read
er can work with buffers of uninitialized
memory. Read more
Creates a “by reference” adapter for this instance of Read
. Read more
Creates an adapter which will chain this stream with another. Read more
Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Read more
Write a buffer into this writer, returning how many bytes were written. Read more
Attempts to write an entire buffer into this writer. Read more
Writes a formatted string into this writer, returning any error encountered. Read more
can_vector
)Determines if this Write
r has an efficient write_vectored
implementation. Read more
write_all_vectored
)Attempts to write multiple buffers into this writer. Read more