jepsen.util — jepsen 0.1.10

Kitchen sink

*relative-time-origin* clj

all-jdk-loggers clj

(all-jdk-loggers)

buf-size clj

chunk-vec clj

(chunk-vec n v)

Partitions a vector into reducibles of size n (somewhat like partition-all) but uses subvec for speed.

(chunk-vec 2 [1])     ; => ([1])
(chunk-vec 2 [1 2 3]) ; => ([1 2] [3])

coll clj

(coll thing-or-things)

Wraps non-coll things into singleton lists, and leaves colls as themselves. Useful when you can take either a single thing or a sequence of things.

compare< clj

(compare< a b)

Like <, but works on any comparable objects, not just numbers.

concat-files! clj

(concat-files! out fs)

Appends contents of all fs, writing to out. Returns fs.

drop-common-proper-prefix clj

(drop-common-proper-prefix cs)

Given a collection of sequences, removes the longest common proper prefix from each one.

exception? clj

(exception? x)

Is x an Exception?

fast-last clj

(fast-last coll)

Like last, but O(1) on counted collections.

fcatch clj

(fcatch f)

Takes a function and returns a version of it which returns, rather than throws, exceptions.

fraction clj

(fraction a b)

a/b, but if b is zero, returns unity.

history->latencies clj

(history->latencies history)

Takes a history--a sequence of operations--and emits the same history but with every invocation containing two new keys:

:latency the time in nanoseconds it took for the operation to complete. :completion the next event for that process

inc* clj

(inc* x)

Like inc, but (inc nil) => 1.

integer-interval-set-str clj

(integer-interval-set-str set)

Takes a set of integers and yields a sorted, compact string representation.

lazy-atom clj

(lazy-atom f)

An atom with lazy state initialization. Calls (f) on first use to provide the initial value of the atom. Only supports swap/reset/deref. Reset bypasses lazy initialization. If f throws, behavior is undefined (read: proper fucked).

letr clj/s macro

(letr bindings & body)

Let bindings, plus early return.

You want to do some complicated, multi-stage operation assigning lots of variables--but at different points in the let binding, you need to perform some conditional check to make sure you can proceed to the next step. Ordinarily, you'd intersperse let and if statements, like so:

(let [res (network-call)]
  (if-not (:ok? res)
    :failed-network-call

    (let [people (:people (:body res))]
      (if (zero? (count people))
        :no-people

        (let [res2 (network-call-2 people)]
          ...

This is a linear chain of operations, but we're forced to nest deeply because we have no early-return construct. In ruby, we might write

res = network_call
return :failed_network_call if not x.ok?

people = res[:body][:people]
return :no-people if people.empty?

res2 = network_call_2 people
...

which reads the same, but requires no nesting thanks to Ruby's early return. Clojure's single-return is usually a boon to understandability, but deep linear branching usually means something like

• Deep nesting (readability issues)
• Function chaining (lots of arguments for bound variables)
• Throw/catch (awkward exception wrappers)
• Monadic interpreter (slow, indirect)

This macro lets you write:

(letr [res    (network-call)
       _      (when-not (:ok? res) (return :failed-network-call))
       people (:people (:body res))
       _      (when (zero? (count people)) (return :no-people))
       res2   (network-call-2 people)]
  ...)

letr works like let, but if (return x) is ever returned from a binding, letr returns x, and does not evaluate subsequent expressions.

If something other than (return x) is returned from evaluating a binding, letr binds the corresponding variable as normal. Here, we use _ to indicate that we're not using the results of (when ...), but this is not mandatory. You cannot use a destructuring bind for a return expression.

letr is not a true early return--(return x) must be a terminal expression for it to work--like (recur). For example,

(letr [x (do (return 2) 1)]
  x)

returns 1, not 2, because (return 2) was not the terminal expression.

return only works within letr's bindings, not its body.

letr-let-if clj

(letr-let-if groups body)

Takes a sequence of binding groups and a body expression, and emits a let for the first group, an if statement checking for a return, and recurses; ending with body.

letr-partition-bindings clj

(letr-partition-bindings bindings)

Takes a vector of bindings [sym expr, sym' expr, ...]. Returns binding-groups: a sequence of vectors of bindgs, where the final binding in each group has an early return. The final group (possibly empty!) contains no early return.

letr-rewrite-return clj

(letr-rewrite-return expr)

Rewrites (return x) to (Return. x) in expr. Returns a pair of [changed? expr], where changed is whether the expression contained a return.

linear-time-nanos clj

(linear-time-nanos)

A linear time source in nanoseconds.

local-time clj

(local-time)

Drops millisecond resolution

log clj

(log & things)

log-op clj

(log-op op)

Logs an operation and returns it.

log-print clj

(log-print _ & things)

logger clj

longest-common-prefix clj

(longest-common-prefix cs)

Given a collection of sequences, finds the longest sequence which is a prefix of every sequence given.

majority clj

(majority n)

Given a number, returns the smallest integer strictly greater than half.

map-kv clj

(map-kv f m)

Takes a function (f [k v]) which returns [k v], and builds a new map by applying f to every pair.

map-vals clj

(map-vals f m)

Maps values in a map.

max-by clj

(max-by f coll)

Finds the maximum element of a collection based on some (f element), which returns Comparables. If coll is empty, returns nil.

maybe-number clj

(maybe-number s)

Tries reading a string as a long, then double, then string. Passes through nil. Useful for getting nice values out of stats APIs that just dump a bunch of heterogenously-typed strings at you.

meh clj/s macro

(meh & body)

Returns, rather than throws, exceptions.

min-by clj

(min-by f coll)

Finds the minimum element of a collection based on some (f element), which returns Comparables. If coll is empty, returns nil.

ms->nanos clj

(ms->nanos ms)

mute clj/s macro

(mute & body)

mute-jdk clj/s macro

(mute-jdk & body)

name+ clj

(name+ x)

Tries name, falls back to pr-str.

nanos->ms clj

(nanos->ms nanos)

nanos->secs clj

(nanos->secs nanos)

nemesis-intervals clj

(nemesis-intervals history)

Given a history where a nemesis goes through :f :start and :f :stop transitions, constructs a sequence of pairs of :start and :stop ops. Since a nemesis usually goes :start :start :stop :stop, we construct pairs of the first and third, then second and fourth events. Where no :stop op is present, we emit a pair like [start nil].

op->str clj

(op->str op)

Format an operation as a string.

poly-compare clj

(poly-compare a b)

Comparator function for sorting heterogenous collections.

polysort clj

(polysort coll)

Sort, but on heterogenous collections.

pprint-str clj

(pprint-str x)

print-history clj

(print-history history)

(print-history printer history)

Prints a history to the console.

prn-op clj

(prn-op op)

Prints an operation to the console.

processors clj

(processors)

How many processors on this platform?

pwrite-history! clj

(pwrite-history! f history)

(pwrite-history! f printer history)

Writes history, taking advantage of more cores.

rand-nth-empty clj

(rand-nth-empty coll)

Like rand-nth, but returns nil if the collection is empty.

random-nonempty-subset clj

(random-nonempty-subset nodes)

A randomly selected, randomly ordered, non-empty subset of the given collection.

real-pmap clj

(real-pmap f coll)

Like pmap, but launches futures instead of using a bounded threadpool.

relative-time-nanos clj

(relative-time-nanos)

Time in nanoseconds since relative-time-origin

retry clj/s macro

(retry dt & body)

Evals body repeatedly until it doesn't throw, sleeping dt seconds.

secs->nanos clj

(secs->nanos s)

sequential clj

(sequential thing-or-things)

Wraps non-sequential things into singleton lists, and leaves sequential things or nil as themselves. Useful when you can take either a single thing or a sequence of things.

sleep clj

(sleep dt)

High-resolution sleep; takes a (possibly fractional) time in ms.

spy clj

(spy x)

time- clj/s macro

(time- & body)

timeout clj/s macro

(timeout millis timeout-val & body)

Times out body after n millis, returning timeout-val.

with-relative-time clj/s macro

(with-relative-time & body)

Binds relative-time-origin at the start of body.

with-retry clj/s macro

(with-retry initial-bindings & body)

It's really fucking inconvenient not being able to recur from within (catch) expressions. This macro wraps its body in a (loop [bindings] (try ...)). Provides a (retry & new bindings) form which is usable within (catch) blocks: when this form is returned by the body, the body will be retried with the new bindings.

with-thread-name clj/s macro

(with-thread-name thread-name & body)

Sets the thread name for duration of block.

write-history! clj

(write-history! f history)

(write-history! f printer history)

Writes a history to a file.