Used to atomically return a dirty object to the pool and then use the
space freed by this object to get another object. Unlike
`put(is_dirty=True)` followed by `get`, a concurrent waiter cannot take
away our space from us.
A piece of `get` was refactored to a private function `_build_and_get`,
this piece is also used in `replace_dirty`.
The pool usage was kind of awkward previously: if the user of a pool
decided that a previously borrowed object should no longer be used,
it was their responsibility to destroy the object (releasing associated
resources and so on) and then call `steal()` on the pool to free space
for a new object.
Change the interface. Now the `Pool` constructor obtains a `destroy`
function additionally to the `build` function. The user calls the
function `put` to return both objects that are still usable and those
aren't. For the latter, they set `is_dirty=True`. The pool will
'destroy' the object with the provided function, which could mean e.g.
releasing associated resources.
For example, instead of:
```
if self.cluster.is_dirty:
self.clusters.stop()
self.clusters.release_ips()
self.clusters.steal()
else:
self.clusters.put(self.cluster)
```
we can now use:
```
self.clusters.put(self.cluster, is_dirty=self.cluster.is_dirty)
```
(assuming that `self.clusters` is a pool constructed with a `destroy`
function that stops the cluster and releases its IPs.)
Also extend the interface of the context manager obtained by
`instance()` - the user must now pass a flag `dirty_on_exception`. If
the context manager exists due to an exception and that flag was `True`,
the object will be considered dirty. The dirty flag can also be set
manually on the context manager. For example:
```
async with (cm := pool.instance(dirty_on_exception=True)) as server:
cm.dirty = await run_test(test, server)
# It will also be considered dirty if run_test throws an exception
```
Instead of complex async with logic, use manual cluster pool handling.
Revert the discard() logic in Pool from a recent commit.
Signed-off-by: Alejo Sanchez <alejo.sanchez@scylladb.com>
This will be used to specify a custom logger when building new clusters
before starting tests, allowing to easily pinpoint which tests are
waiting for clusters to be built and what's happening to these
particular clusters.
Some tests mark clusters as 'dirty', which makes them non-reusable by
later tests; we don't want to return them to the pool of clusters.
This use-case was covered by the `add_one` function in the `Pool` class.
However, it had the unintended side effect of creating extra clusters
even if there were no more tests that were waiting for new clusters.
Rewrite the implementation of `Pool` so it provides 3 interface
functions:
- `get` borrows an object, building it first if necessary
- `put` returns a borrowed object
- `steal` is called by a borrower to free up space in the pool;
the borrower is then responsible for cleaning up the object.
Both `put` and `steal` wake up any outstanding `get` calls. Objects are
built only in `get`, so no objects are built if none are needed.
Closes#11558
Pool.get() might have waiting callers, so if an item is not returned
to the pool after use, tell the pool to add a new one and tell the pool
an entry was taken (used for total running entries, i.e. clusters).
Use it when a ScyllaCluster is dirty and not returned.
While there improve logging and docstrings.
Issue reported by @kbr-.
Signed-off-by: Alejo Sanchez <alejo.sanchez@scylladb.com>
Closes#11546
