add password support for redis connects in cache and session

In unit test, we write cache file often and
opcache might fail to detect changes. It will
be nice to invalidate opcode cache to ensure
we have the correct file_exists status

Russell Smith authored Jun 07, 2016 and Mark Nelson committed Mar 02, 2017

It is now safe to cache a reference to a cache and expect consistent results.

Changing identifiers altered cache results where a reference was
held to the cache. Identifiers have been set to be cached with
identifiers included so the caches are separate.

As a consequence of this it was identified that invalidation events
and identifiers don't easily work together as an event can't determine
which identifiers should be used for cache invalidation.  So invalidation
events have been made incompatible with identifiers being set.  No core
code used this combination as it's not possible to understand any expected
behaviour.

Event invalidation for application and session caches was centralised to the same
location.  The only difference was the name of the lastinvalidation variable. This
improves support and consistency of invalidation code.

This unit test is not really verifying that internally igbinary
in being used but just igbinary availability and, by double
serializing, that it works for a semi-complex object.

The test will be skipped if igbinary is not available.

version = 2016120500 release version
requires= 2016112900 current rc4 version

Some windows only have 1/100 microtime resolution
so a lot of times it does not advance enough.

Previously a purge_store was only purging caches but it was leaving a
reference to the store instance for the cache definition.

As a result, the cache was never cleared away correctly and, in cases
where the cache store makes a TCP connection to a backend system, the
number of open sockets was increasing for each store instance.

After a complete purge, as found in the unit test reset, the cache
definitions should be both purged and removed.

This change should also lead to a drop in memory consumption for unit
tests as there will no longer be references to unused definition stores.

After store is created, it should be checked if
it's ready before calling initialise

Ensure that the cache store requirements are met prior to attempting
to instantiate a class.  Many of the constructors create connections
to external services requiring the installation and availability of
classes that are specified in are_requirements_met().  If they are
not checked properly you end up with PHP Fatal errors rather than
falling back to a different store that is capabable without the
the extra classes loaded.

purge_all() and purge_by_definition() look in the configuration
for which caches are available and then creates them to purge them.
The configuration stores the values used by initialise(), not
initialise_unit_test_instance() and would therefore fail to purge
all caches if they were not purged by another means.

In the case of filestore, it's purged by unit tests, in the case
of memcache(d), it purges the whole store when a single definition
is requested.

Therefore all configuration was moved into the configuration file
during unit tests and does not have any special override codes in
the unit test infrastructure.

This code was originally taken from; https://github.com/durana/moodle-cachestore_redis
Special thanks to Mark Nielsen and Adam Durana for their work on this.

Since the original import;
- Mode session support has been added.
- Some cleanup of names has been made.
- Data guarantee and references support was added.

If alternative cache store is sued, then set the class
and warn user about this.

There is no second parameter in the api
and identifier should be set by set_identifiers

When APCu is enabled, but the CLI is not it's possible for
calls to enable APCu to fail because it's not configured on the
command line.

Frederic Massart authored Aug 19, 2016 and Dan Poltawski committed Sep 23, 2016

Part of MDL-55071

We now use APCu as it's support by PHP7 and provides the
functionality we need.

Static cache has a very flexible storage capability
and does not need all the checks performed on it.
Enabling dereferencing handling and multiple identifiers
removes a lot of unneeded overhead for request caches that
have many get calls.

The changes were modelled on the static acceleration changes
done in MDL-53208.

When a cachable object is store in the static cache from
the backing store, it was incorrect serialised rather than
using the wake function.  This has been resolved and tests added.

During the investigation into cacheable_object, it was discovered
that set_identifiers never removes identifiers when you call it,
so set_identifiers(array('a')) and set_identifiers(array('b')) really
resulted in array('a','b') as the identifiers rather than 'b'.

The fix for this issue depends on the set_identifiers fix and
they have been coupled together as a result.

version = 2016052300 release version
requires= 2016051900 current rc1 version

When added a memcached instance you can now select whether the cache is
being shared by other applications. The setting will determine the
purging strategy.

Shared caches will have individual keys deleted while dedicated caches
will have the entire cache purged (better performance over networks).

Note: This option only works with the correct version of the php
memcached extension and with the multi-site safe changes.