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Unit srfi-18

A simple multithreading package. This threading package follows largely the specification of SRFI-18. For more information see the documentation for SRFI-18.

Notes:

• thread-start! accepts a thunk (a zero argument procedure) as argument, which is equivalent to (thread-start! (make-thread THUNK)).
• thread-sleep! accepts a seconds real number value in addition to a time object.
• When an uncaught exception (i.e. an error) is signalled in a thread other than the primordial thread and warnings are enabled (see: enable-warnings, then a warning message is written to the port that is the value of (current-error-port).
• Blocking I/O will block all threads, except for some socket operations (see the section about the tcp unit). An exception is the read-eval-print loop on UNIX platforms: waiting for input will not block other threads, provided the current input port reads input from a console.
• It is generally not a good idea for one thread to call a continuation created by another thread, if dynamic-wind is involved.
• When more than one thread compete for the current time-slice, the thread that was waiting first will become the next runnable thread.
• The dynamic environment of a thread consists of the following state:
  • The current input-, output- and error-port
  • The current exception handler
  • The values of all current parameters (created by make-parameter)
  • Any pending dynamic-wind thunks.
• When an error is triggered inside the execution context of a thread, the default exception-handler will simply terminate the thread (and store the error condition for later use). Pending dynamic-wind thunks will not be invoked. Use a custom exception handler for the thread in that case.

The following procedures are provided, in addition to the procedures defined in SRFI-18:

thread-signal!

[procedure] (thread-signal! THREAD X)

This will cause THREAD to signal the condition X once it is scheduled for execution. After signalling the condition, the thread continues with its normal execution.

thread-quantum

[procedure] (thread-quantum THREAD)

Returns the quantum of THREAD, which is an exact integer specifying the approximate time-slice of the thread in milliseconds.

thread-quantum-set!

[procedure] (thread-quantum-set! THREAD QUANTUM)

Sets the quantum of THREAD to QUANTUM.

thread-suspend!

[procedure] (thread-suspend! THREAD)

Suspends the execution of THREAD until resumed.

thread-resume!

[procedure] (thread-resume! THREAD)

Readies the suspended thread THREAD.

thread-wait-for-i/o!

[procedure] (thread-wait-for-i/o! FD [MODE])

Suspends the current thread until input (MODE is #:input), output (MODE is #:output) or both (MODE is #:all) is available. FD should be a file-descriptor (not a port!) open for input or output, respectively.

time->milliseconds

[procedure] (time->milliseconds TIME)

Converts a time object (as created via current-time) into an exact integer representing the number of milliseconds since process startup.

milliseconds->time

[procedure] (milliseconds->time ms)

Converts into a time object an exact integer representing the number of milliseconds since process startup.

This procedure may be useful in combination with thread-sleep! when your compilation unit is using (declare fixnum-arithmetic). In that case you won't be able to pass an inexact value to thread-sleep!, but you can do the following:

(define (thread-sleep!/ms ms)
  (thread-sleep!
   (milliseconds->time (+ ms (current-milliseconds)))))

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