Class SessionContainer

Known Subclasses:

DatabaseSessionContainer

This is a container for sessions.

A container class is needed because:

• We need to be able to call certain methods such as cleanup without actually creating a Session instance. Hence, these methods obviously can't be instance methods of the Session class.
• I want subclasses to be able to override some of these methods.

On the other hand, no instance state is kept, so one instance of this class is just as good as another. All state is kept in the class. I'd use a singleton, but the version of Python I'm stuck with doesn't have class methods.

Concerning locking: in general, a global lock (of some sort) should be used so that creating, deleting, reading, and writing sessions is serialized. However, it is not necessary to have a lock for each session. If a user wishes to use two browser windows at the same time, the last writer wins.

Concerning aquarium.util.AquariumClass: this class does not subclass aquarium.util.AquariumClass and does not require a ctx parameter in its constructor. Subclasses may choose to mixin aquarium.util.AquariumClass as necessary, but they will then require a ctx in their constructors. aquarium.util.Aquarium is aware of this.

This base class is useful for mutlithreaded environments. For other environments, such as CGI, it simply provides an API.

The following class level constants are defined:

SID_LENGTH

This is the length of standard sid's.

These are needed since not all "mutexes" provide the same API, unfortunately:

_acquire

Acquire the global lock.

_release

Release the global lock.

The following protected class variables are used:

_lock

This is the global lock. It is initialized statically. (This base class uses threading.Lock. Subclasses can set this to something different if appropriate.)

_sessions

This is the global dictionary of sessions.

sessionContainer._acquire()
try:
    changeTime()
    sessionContainer.adjustTime(deltaSeconds)
finally:
    sessionContainer._release()