Class: Datadog::CRubyBuffer

Inherits:
Buffer
  • Object
show all
Defined in:
lib/ddtrace/buffer.rb

Overview

Buffer that stores objects, has a maximum size, and can be safely used concurrently with CRuby.

Because singular +Array+ operations are thread-safe in CRuby, we can implement the trace buffer without an explicit lock, while making the compromise of allowing the buffer to go over its maximum limit under extreme circumstances.

On the following scenario:

  • 4.5 million spans/second.
  • Pushed into a single CRubyTraceBuffer from 1000 threads.

This implementation allocates less memory and is faster than ThreadSafeBuffer.

See Also:

Direct Known Subclasses

CRubyTraceBuffer

Constant Summary collapse

FIXNUM_MAX =

A very large number to allow us to effectively drop all items when invoking slice!(i, FIXNUM_MAX).

(1 << 62) - 1

Instance Method Summary collapse

Methods inherited from Buffer

#close, #closed?, #concat, #empty?, #initialize, #length, #pop, #push

Constructor Details

This class inherits a constructor from Datadog::Buffer

Instance Method Details

#replace!(item) ⇒ Object

Add a new trace in the local queue. This method doesn't block the execution even if the buffer is full. In that case, a random trace is discarded.



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# File 'lib/ddtrace/buffer.rb', line 204

def replace!(item)
  # Ensure buffer stays within +max_size+ items.
  # This can happen when there's concurrent modification
  # between a call the check in `full?` and the `add!` call in
  # `full? ? replace!(item) : add!(item)`.
  #
  # We can still have `@items.size > @max_size` for a short period of
  # time, but we will always try to correct it here.
  #
  # `slice!` is performed before `delete_at` & `<<` to avoid always
  # removing the item that was just inserted.
  #
  # DEV: `slice!` with two integer arguments is ~10% faster than
  # `slice!` with a {Range} argument.
  @items.slice!(@max_size, FIXNUM_MAX)

  # We should replace a random trace with the new one
  replace_index = rand(@max_size)
  @items[replace_index] = item
end