Description
Reports terminal cancellation. File I/O raises this only after the kernel has relinquished the caller's buffer.
Await_Request
procedure Await_Request (Item : in out Request_Waiter)
Wait until the one-shot request state becomes terminal.
Parameters
- Item
Entry-bearing cancellation state to wait on
Await_Request
procedure Await_Request (Item : in out Token)
Wait until Request records terminal cancellation. Task-only waiting does not allocate a descriptor.
Parameters
- Item
Token on which to wait
Operation_Cancelled
Operation_Cancelled : exception;
Reports terminal cancellation. File I/O raises this only after the kernel has relinquished the caller's buffer.
Request
procedure Request (Item : in out Token)
Record cancellation and wake every operation waiting on this token. Program_Error is raised when an existing borrowed wake descriptor cannot be signalled. Cancellation remains recorded when signalling fails. The signal and any EINTR retry occur after the state lock exits.
Parameters
- Item
Token on which to record cancellation
Request_Waiter
type Request_Waiter is synchronized interface;
Entry-bearing view for an abortable select. The Token must outlive the selected call. Use Stop.Wait_Event.Await_Request as the trigger.
Requested
function Requested (Item : Token) return Boolean
Inspect the one-shot state without allocating a wake descriptor.
Parameters
- Item
Token to inspect
Return value
True once Request records cancellation, including when wake signaling subsequently fails
Token
type Token is tagged limited private;
Thread-safe one-shot source. Request is idempotent and cannot be reset. Finalization releases lazily created wake descriptors after all borrowing operations have left scope.
Wait_Event
function Wait_Event (Item : aliased in out Token) return not null access Request_Waiter'Class
Borrow the protected entry for an abortable select.
Parameters
- Item
Token that must outlive the select
Return value
Entry-bearing view of Item's one-shot state
Wait_Source
procedure Wait_Source (Item : in out Token; FD : out Interfaces.C.int; Already_Requested : out Boolean)
Borrow the readable wake descriptor. Ownership remains with Token; callers must not close it, and Token must outlive the wait. No descriptor is allocated when cancellation was already requested. Descriptor creation occurs outside the protected state lock.
Parameters
- Item
Token that owns the borrowed descriptor
- FD
Borrowed descriptor, or -1 when already requested
- Already_Requested
True when Request preceded this call
Raised exceptions
- Program_Error
Wake descriptor creation fails