Parallelism is hard. Parfait provides some primitives to make it easier. Particularly, Parfait focuses on providing primitives for working with parallelism in a functional way, using threads to return values instead of perform side effects.
Everything in Parfait is a shameless port of Clojure's basic parallelism primitives into Common Lisp. For a more in-depth explanation, see Clojure for the Brave and True, or consult the Clojure documentation.
In addition to the concurrency primitives, Parfait also provides a
readtable for easier usage of DEREF, called
PARFAIT:DEREF-READTABLE. Under this readtable, ^X is the equivalent
of (DEREF X); the readtable should be merged into another before being
used. Make sure that the readtables do not conflict in their usage of
the macro character ^, and REQUIRE or ASDF:LOAD-SYSTEM on
parfait+readtable, instead of just parfait.
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DEREF OBJ
Return the value contained by OBJ, blocking until the value is available.
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FUTURE &BODY BODY
Starts a new thread, which runs BODY. Returns a promise; dereferencing the promise will return the value of BODY. BODY will only run once, atomically, and DEREFs after the first will not block.
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DELAY &BODY BODY
Returns a delay; dereferencing the delay will return the value of BODY. Unlike a function object, BODY will only run once, atomically, and DEREFs after the first will not block.
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PROMISE
Returns a promise. Attempting to dereference this promise will block until a value is DELIVERed. Allows for decoupling of variable declaration and binding until necessary.
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DELIVER PROMISE VALUE
Set the value of a promise and unblock any threads trying to dereference it. Does nothing, if the promise has already been delivered.