class twisted.internet.tcp._IFileDescriptorReservation(Interface): (source)
Known implementations: twisted.internet.tcp._FileDescriptorReservation, twisted.internet.tcp._NullFileDescriptorReservation
An open file that represents an emergency reservation in the process' file descriptor table. If Port encounters EMFILE on accept(2), it can close this file descriptor, retry the accept so that the incoming connection occupies this file descriptor's space, and then close that connection and reopen this one.
Calling _IFileDescriptorReservation.reserve attempts to open the reserve file descriptor if it is not already open. _IFileDescriptorReservation.available returns True if the underlying file is open and its descriptor claimed.
_IFileDescriptorReservation instances are context managers; entering them releases the underlying file descriptor, while exiting them attempts to reacquire it. The block can take advantage of the free slot in the process' file descriptor table accept and close a client connection.
Because another thread might open a file descriptor between the time the context manager is entered and the time accept is called, opening the reserve descriptor is best-effort only.
| Method | available | Is the reservation available? |
| Method | reserve | Attempt to open the reserved file descriptor; if this fails because of EMFILE, internal state is reset so that another reservation attempt can be made. |
| Method | __enter__ | Release the underlying file descriptor so that code within the context manager can open a new file. |
| Method | __exit__ | Attempt to re-open the reserved file descriptor. See reserve for caveats. |
Release the underlying file descriptor so that code within the context manager can open a new file.
Attempt to re-open the reserved file descriptor. See reserve for caveats.
| Parameters | excType | See object.__exit__ |
| excValue | See object.__exit__ | |
| traceback | See object.__exit__ |