Merge pull request #93 from chenyijun266846/perf_setnx

perf: add setnx2

Merge pull request #85 from rfyiamcool/feat/add_setnx

feat: add setnx (if not exists, set kv)

Merge pull request #84 from idsulik/added-key-method-to-item

Added Key() method to Item

Merge pull request #78 from karlseguin/control_stop

Refactor control messages + Stop handling

On delete, always set promotions == -2 and node == nil

Also, item.promotions doesn't need to be loaded/stored using atomic. Once upon a
time it did. Cache was updated long ago to not use atomic operations on it, but
LayeredCache wasn't. They are both consistent now (they don't use atomic
operations).

Fixes: #76

Fix memory leak

As documented in #76, an entry which
is both GC'd and deleted (either via a delete or an update) will result in the
internal link list having a nil tail (because removing the same node multiple times
from the linked list does that).

doDelete was already aware of "invalid" nodes (where item.node == nil), so the
solution seems to be as simple as setting item.node = nil during GC.

always run tests with -race and withint caching

add ForEachFunc

Merge pull request #52 from gopalmor/master

Avoid blocking if promotables channel is full.

go mod version