thread.ss: Thread Utilities
(consumer-thread f [init]) PROCEDURE
Returns two values: a thread descriptor for a new thread, and a
procedure with the same arity as f.10 When the returned procedure is applied,
its arguments are queued to be passed on to f, and void is
immediately returned. The thread created by consumer-thread
dequeues arguments and applies f to them, removing a new
set of arguments from the queue only when the previous application of
f has completed; if f escapes from a normal return (via
an exception or a continuation), the f-applying thread
terminates.
The init argument is a procedure of no arguments; if it is
provided, init is called in the new thread immediately after the
thread is created.
(copy-port input-port output-port ···1) PROCEDURE
Reads data from input-port and writes it back out to
output-port, returning when input-port produces
eof. The copy is efficient, and without significant buffer
delays (i.e., a character that becomes available on input-port
is immediately transferred to output-port, even if future reads
on input-port must block).
This function is often called from a ``background'' thread to continuously pump data from one stream to another.
If multiple output-ports are provided, case data from
input-port is written to every output-port. The different
output-ports block output to each other, because each quantum
of data read from input-port is written completely to one
output-port before moving to the next output-port. The
output-ports are written in the provided order, so non-blocking
ports (e.g., to a file) should be placed first in the argument list.
(dynamic-disable-break thunk) PROCEDURE
Invokes thunk and returns the result. During the application of
thunk, breaks are disabled.
(dynamic-enable-break thunk) PROCEDURE
Invokes thunk and returns the result. During the application of
thunk, breaks are enabled.
(make-single-threader) PROCEDURE
Returns a new procedure that takes any thunk and applies it. When this procedure is applied to any collection of thunks by any collection of threads, the thunks are applied sequentially across all threads.
(merge-input a-input-port b-input-port [limit-k]) PROCEDURE
Accepts two input ports and returns a new input port. The new port merges the data from two original ports, so data can be read from the new port whenever it is available from either original port. The data from the original ports are interleaved. When EOF has been read from an original port, it no longer contributes characters to the new port. After EOF has been read from both original ports, the new port returns EOF. Closing the merged port does not close the original ports.
The optional limit-k argument limits the number of characters to
be buffered from a-input-port and b-input-port, so that
the merge process does not advance arbitrarily beyond the rate of
consumption of the merged data. A #f value disables the
limit; the default is 4096.
(run-server port-k session-proc session-timeout) PROCEDURE
Executes a TCP server on the port inidicated by port-k. When a
connection is made by a client, session-proc is called with two
values: an input port to receive from the client, and an output port
to send to the client.
Each client connection, or session, is managed by a new
custodian, and each call to session-proc occurs in a new thread
(managed by the session's custodian). If the thread executing
session-proc terminates for any reason (e.g., sesson-proc
returns), the session's custodian is shut down. Consequently,
session-proc need not close the ports provded to it. Breaks are
enabled in the session thread if breaks are enabled when
run-server is called.
If session-timeout is not #f, then it must be a
non-negative number specifying the time in seconds that a session
thread is allowed to run before it is sent a break signal. Then, if
the thread runs longer than (* session-timeout 2) seconds,
then the session's custodian is shut down. If session-timeout
is #f, a session thread can run indefinitely.
The run-server procedure loops to serve client connections, so
it never returns. If a break occurs, the loop will cleanly shut down
the server, but it will not terminate active sessions.
(with-semaphore s thunk) PROCEDURE
Calls semaphore-wait on s, then invokes thunk with
no arguments, and then calls semaphore-post on s. The
return value is the result of calling thunk.
10 The returned
procedure actually accepts any number of arguments, but immediately
raises exn:application:arity if f cannot accept the
provided number of arguments.