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cowan

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98.14.172.204

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ThreadsCowan

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== Threads ==

This is a simple threads proposal based on SRFI-18, but eliminating `thread-terminate!`, which has dodgy semantics: it does not give the thread any chance to recover.  Its Java equivalent, `Thread.destroy()`, is deeply deprecated for the same reason.

== Thread procedures ==

`(current-thread)`

Returns the current thread.

`(thread? `''obj''`)`

Returns `#t` if ''obj'' is a thread, otherwise returns `#f`.

`(make-thread `''thunk''` `[''name'']`)`

Constructs and returns a new thread.  ''Thunk'' is a procedure returning one value; ''name'' can be any Scheme object.

A thread has the following fields: ''name'', ''specific'', ''end-result'', ''end-condition'', and ''resource-list'', a list of communication resources it owns.   The first four fields can contain any Scheme object, and default to an unspecified value.  The ''name'' field is set from the optional ''name'' argument: it is an arbitrary Scheme object which identifies the thread (useful for debugging).

This thread is not automatically made runnable (the procedure `thread-start!` must be used to start it).  A thread's execution consists of a call to ''thunk'' with a continuation that causes the thread to store the value of ''thunk'' in its ''end-result'' field, abandon all resources in ''resource-list'', and finally terminate. The dynamic-wind stack of the initial continuation is empty.

The thread inherits the dynamic environment from the current thread, except that the exception handler is bound to a procedure which causes the thread to store in its ''end-condition'' field a FIXME object, abandon all resources in ''resource-list'', and finally terminate.


`(thread-name `''thread''`)`

Returns the content of the ''name'' field  of ''thread''.

`(thread-specific `''thread''`)`

Returns the content of the ''specific'' field of ''thread''.

`(thread-specific-set! `''thread''` `''obj''`)`

Sets ''specific'' field of ''thread'' to ''obj''.  Returns unspecified values.

`(thread-start! `''thread''`)`

Makes ''thread'' (which must be a new thread) runnable.  Returns ''thread''.  Thread creation and thread activation are separated in order to avoid the race condition that would occur if the created thread tries to examine a data structure in which the current thread stores the created thread.

`(thread-yield!)`

The current thread exits the running state as if its quantum had expired. Returns unspecified values.

`(thread-sleep! `''timeout''`)`

The current thread waits until the value of `(elapsed-time)` is greater than or equal to ''timeout''. This blocks the thread only if ''timeout'' represents a point in the future.  Returns unspecified values.

`(thread-join! `''thread'' [''timeout'' [''timeout-result'']]`)`

The current thread waits until ''thread'' terminates (normally or not) or until the timeout is reached if ''timeout'' is supplied. If ''timeout'' is reached, returns ''timeout-result'' if it is supplied, otherwise a FIXME exception is raised. If ''thread'' terminated normally, the content of its ''end-result'' field is returned, otherwise the content of the ''end-condition'' field is raised.

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2010-12-07 11:24:00