BC did not take a lock for `hash-clear!`. Maybe the intent was that a
lock isn't needed from the perspective of `hash-clear!` when it isn't
traversing the table, but failing to take a lock before modifying the
table can break other operations (that do take a lock) in progress.
Furthermore, some iterations that intentionally did not take a lock
also did not guard against changes well enough. Various repairs here
avoid crashes, and now `hash-clear!` consistently takes a lock.
CS had a similar (but more subtle and more limited) instance of the
problem in `hash-map` and `hash-for-each`. That problem is corrected
(without adding any new lock acquisitions).
The existing CS implementation of `equal-hash-code` for hash tables
takes a lock more than the BC implementation. A possibly surprising
result: when attempting to add a mutable hash table to itself as part
of a key, the `hash-set!` can block forever on the hash table's lock,
instead of doing something more random as a result of having a mutated
key. The documentation now notes that possibility.
Related to #3738
Update the Guide's performance section with current information for
Racket CS, and also document the Racket CS compilation mode and
inspection environment variables. Make a couple of environment
variables work more consistently: PLTDISABLEGC for CS and PLT_ZO_PATH
for BC.
* Add support for space-efficient vector and arrow contracts.
When an eleventh contract would be applied to a function or vector,
switch representation for the wrapper and try eliding redundant
checks. The resulting value keeps a constant number of
chaperone/impersonator wrappers regardless of the number of contracts
applied to it, and won't run any (provably) redundant checks.
This avoids a pathological case where, e.g., a function crosses a
boundary inside a loop, and gets wrapped N times (or worse, 2^N).
The optimization for function contracts currently only applies for
fixed-arity functions and contracts, and only for functions with known
result-arity of 1. These limitations are not fundamental.
Checking specific checks is not as optimized as for regular arrow
contracts yet. (Specifically: arity-specific wrappers and
tail-marks-match support is missing.) Again, not a fundamental
limitation.
Further described in the OOPSLA 2018 Paper: "Collapsible Contracts: Fixing a Pathology of Gradual Typing"
In collaboration with Ben Greenman, Christophe Scholliers, Robby Findler, and Vincent St-Amour.
Allow a single argument to comparison functions like `<`, and
support the same arities as the generic version for fixnum and
flonum operations like `fx+` or `fl+`.
Although "macOS" is the correct name for Apple's current desktop OS,
we've decided to go with "Mac OS" to cover all of Apple's Unix-like
desktop OS versions. The label "Mac OS" is more readable, clear in
context (i.e., unlikely to be confused with the Mac OSes that
proceeded Mac OS X), and as likely to match Apple's future OS names
as anything.
Port `examples`, `interactions`, etc., to use the new `examples`
form of `scribble/examples`. The main intended effect is to ensure
that errors are produced by examples only as specifically
indicated.
