Debugger: File breakpoint storage

[chingor13]

Adds a file-based implementation of BreakpointStorageInterface. This will allow windows users to use debugger.

Note: we're using flock for attempting to make our file read/writes safe between 2 separate processes.

[dwsupplee]

This may be helpful: https://github.com/GoogleCloudPlatform/google-cloud-php/tree/master/src/Core/Lock

We could update the interface to pass in a flag to use either a blocking or non blocking lock

[chingor13]

Awesome, I'll take a look at those.

[chingor13]

Looks like I also need to add an option for the lock type. In this use case, it's fine to have many readers so we don't need to acquire an exclusive lock when reading.

The new signature would either need to be:

• public function acquire($blocking = true, $exclusive = true) or
• public function acquire(array $options = []) with blocking and exclusive option keys.

edited: blocking defaults to true (unlike symfony) because that's the current behavior for FlockLock

[chingor13]

@dwsupplee Went with public function acquire(array $options = []). For implementations that do not support shared locks, we trigger an E_USER_WARNING and ignore that option.

[dwsupplee]

A cursory look at the second signature SGTM. I am away from my desk for a bit, will review this and #848 tonight :).

[dwsupplee]

Looks really nice! One last little thing I noticed.