INTERFACEThese procedures are functionally equivalent to callingSchedulerPosix ; IMPORT Thread; TYPE WaitResult = {Ready, Error, FDError, Timeout}; PROCEDURE IOWait(fd: INTEGER; read: BOOLEAN; timeoutInterval: LONGREAL := -1.0D0): WaitResult; PROCEDURE IOAlertWait(fd: INTEGER; read: BOOLEAN; timeoutInterval: LONGREAL := -1.0D0): WaitResult RAISES {Thread.Alerted};
select(2)
with a single file descriptor. The major difference is that calls
on IOWait and IOAlertWait do not prevent other threads from
running. If read is TRUE, then the readfds and exceptfds
arguments to select are the singleton set containing fd, and
writefds is the empty set. Otherwise, the writefds and
exceptfds are non-empty, and readfds is empty.
The return value from IOWait and IOAlertWait indicates that
fd was found to be ready for I/O, or that the caller's timeout
interval expired, or that an error occured:
-- Ready indicates that fd was found to be ready for I/O
(according to the value of the read argument). In other
words, a subsequent I/O operation might succeed. If fd is
persistently in such a state, then IOWait and IOAlertWait
will return Ready.
-- Error indicates that a select call executed on behalf
of the caller failed, for instance the supplied fd is not
valid.
-- FDError indicates that fd is valid, but it exhibits an
exceptional condition.
-- Timeout indicates that the caller's timeout expired. The
file descriptor will have been tested at least once before
this result is returned.
IOWait and IOAlertWait block until the argument fd is in a
reportable state, or until timeoutInterval seconds have passed.
If timeoutInterval is negative, an indefinite wait is indicated,
As usual, IOAlertWait is the alertable version, IOWait is the
non-alertable version.
A Ready result from IOWait and IOAlertWait does not guarantee
that I/O is currently possible on fd. For example, any other
thread may preempt during the return sequence and issue a read on
fd.
A standard technique for using these procedures is as follows.
First make reads non-blocking on the file descriptor fd, and then
use a loop of the form:
LOOP status := read (fd, buf, n); IF status = -1 AND errno # EWOULDBLOCK THEN (* error to be handled
ELSIF status = 0 THEN
(* eof reached *)
ELSIF status > 0 THEN
(* status chars available in buf *)
END;
EVAL SchedulerPosix.IOWait(fd, TRUE);
END;
*)
PROCEDURE DisableSwitching ();
PROCEDURE EnableSwitching ();
Increment/decrement the counter that controls whether thread switches may occur. The counter is initialized to zero. If the counter is greater than zero, switching is disabled. It's a checked runtime error to use any thread primitives (e.g. LOCK, Wait, Signal, Yield, ...) that would result in thread switches while switching is disabled.
END SchedulerPosix.