QA/Automation/Projects/Addons/MemChaser/Future Features

Circular Buffer

Usage/Overview

• Main data structure for graphs
• Stores temporary GC (and CC,etc.) values
• Conceptually is a linked list with a cycle from the tail to head, but it would be implemented using an array in JavaScript

Requirements

• Have as little impact on garbage collection as possible
• Have read/write capabilities with events emitted from writes
• Read operations should not post-increment head index and should not delete the element being read

Current Proposal

Source

https://github.com/dglol/memchaser/blob/circular-buffer/extension/lib/circular-buffer.js

Fields

• front
  • index for the front of the buffer

• back
  • index for the back of the buffer

• buffer
  • array building block for this data structure

Methods

• CircularBuffer(length) (Constructor)
  • only required a length to initialize
  • length defaults to 1 if a undefined value or negative number is given

• size() (Necessary)
  • returns the size of the buffer

• read([index]) (Necessary)
  • returns data from [head + index] if a positive index is given
  • else it returns the data at [head] (i.e. index = 0)
  • if index is negative, then it returns data from [tail + index]

• write(data)/push(data) (Necessary)
  • writes data at the [tail] then increments tail index by one
  • emits an event 'bufferWrite'

• pop() (Optional)
  • returns data from [tail] then decrements tail by one

• shift() (Optional)
  • reads from [head], removes the data at [head] and increments head by one

• unshift(data) (Optional)
  • decrements head by one, then writes the data at head

• clear() (Optional)
  • resets the buffer, head index and tail index

• flush() (Not yet implemented)
  • clears the buffer and dumps data onto an array, and sends it

Discussion items

JSON Blob vs Separate Buffers

• A JSON Blob of all the data ({gc: , cc:, etc}) has less overhead but writes would have to be synchronous
• GC and related data occur at different times, so separate buffers allows asynchronous writing

History Graph

Usage/Overview

• Uses the circular buffer as a data structure to hold data points
• Data points are obtained from listening to the event generated by CircularBuffer.Write()
• Data is represented by a bar chart
  • X axis represents the last n data points, where n represents the latest data point
• Data falls off after the circular buffer is full

Moving Graph

Usage/Overview

• Uses the circular buffer as a data structure to hold data points
• Data points are obtained from listening to the event generated by CircularBuffer.Write()
• Data is represented by a line chart
  • X axis represents the last n seconds, where n represents the latest data point
• Data falls off every second

Memory Report per Compartment

Blocked by https://bugzilla.mozilla.org/show_bug.cgi?id=687724