Module selector - IO selector
IO selector.
An IO selector is a server that waits in an efficient way for events on a set of file descriptors; it provides a process-oriented interface to the poll(2) system call (or an equivalent).
To start an IO selector, call selector.start; see SELECTOR.CT for the interface.
Index
-
Group
SELECT- Events to select upon-
Constant
SELECT.READ- A read will not block -
Constant
SELECT.WRITE- A write will not block
-
Constant
-
Channel type
SELECTOR.CT- Interface to an IO selector -
Protocol
SELECTOR.REQ- Requests to an IO selector-
Tag
add- Add a file descriptor to the set being waited upon -
Tag
shutdown- Shut down the selector
-
Tag
-
Channel type
SELECTOR.SIGNAL- Channel bundle used for the selector to signal back to the client -
Protocol
SELECTOR.SIGNAL.REQ- Requests from an IO selector to a waiting process-
Tag
ready- The FD has become ready -
Tag
shutdown- The selector is shutting down
-
Tag
-
Protocol
SELECTOR.SIGNAL.RESP- Responses from a waiting process to an IO selector-
Tag
again- Wait for the FD again -
Tag
remove- Remove the FD from the waiting set
-
Tag
-
Process
selector.add- Register a file descriptor with a selector -
Process
selector.delayed.add- Register a file descriptor with a selector, then send the new signal end down a shared channel -
Process
selector.make.nonblocking- Make a file descriptor non-blocking -
Process
selector.start- Start an IO selector
Declarations
selector.occ:34Process selector.make.nonblocking
PROC selector.make.nonblocking (VAL INT fd)
Make a file descriptor non-blocking. This just sets the O.NONBLOCK flag on the FD.
Parameters:
VAL INT |
fd |
File descriptor |
selector.occ:42Process selector.add
PROC selector.add (SHARED SELECTOR.CT! sel, VAL INT fd, events, RESULT SELECTOR.SIGNAL? svr)
Register a file descriptor with a selector.
selector.occ:58Process selector.delayed.add
PROC selector.delayed.add (SHARED SELECTOR.CT! sel, VAL INT fd, events, SHARED CHAN SELECTOR.SIGNAL? svr.out!)
Register a file descriptor with a selector, then send the new signal end down a shared channel.
Why would you want to do this? It's to avoid a client-server loop if you've got a client that wants to change the set of FDs it selects on: rather than having it add the FD itself (which would mean switching the direction of the client-server relationship), have it fork off this process.
selector.occ:68Process selector.start
PROC selector.start (RESULT SHARED SELECTOR.CT! sel)
Start an IO selector.
selector.inc:31Group SELECT
Events to select upon.
selector.inc:32Constant SELECT.READ
VAL INT SELECT.READ
A read will not block.
selector.inc:33Constant SELECT.WRITE
VAL INT SELECT.WRITE
A write will not block.
selector.inc:37Protocol SELECTOR.SIGNAL.REQ
PROTOCOL SELECTOR.SIGNAL.REQ
Requests from an IO selector to a waiting process.
selector.inc:40Tag ready
ready = 0
The FD has become ready.
selector.inc:42Tag shutdown
shutdown = 1
The selector is shutting down.
selector.inc:46Protocol SELECTOR.SIGNAL.RESP
PROTOCOL SELECTOR.SIGNAL.RESP
Responses from a waiting process to an IO selector.
selector.inc:49Tag again
again = 0
Wait for the FD again.
selector.inc:51Tag remove
remove = 1
Remove the FD from the waiting set.
selector.inc:58Channel type SELECTOR.SIGNAL
CHAN TYPE SELECTOR.SIGNAL
Channel bundle used for the selector to signal back to the client.
This may look dodgy from a C-S perspective, but it should be OK: at any given time, the client-server relationship is only going one way...
selector.inc:65Protocol SELECTOR.REQ
PROTOCOL SELECTOR.REQ
Requests to an IO selector.
selector.inc:71Tag add
add = 0; INT; INT; SELECTOR.SIGNAL!
Add a file descriptor to the set being waited upon.
Parameters:
INT |
fd |
File descriptor (usually non-blocking) |
INT |
events |
Bitwise OR of events to wait for; see SELECT
|
SELECTOR.SIGNAL! |
signal |
Channel bundle to signal over when the event fires |
selector.inc:73Tag shutdown
shutdown = 1
Shut down the selector.
selector.inc:77Channel type SELECTOR.CT
CHAN TYPE SELECTOR.CT
Interface to an IO selector.