Make LogRecord immutable, simplifies concurrency

[bogdandrutu]

Problem Statement

I would propose to separate LogRecord struct into mutable vs immutable and pass immutable to Emit to avoid having to deal with concurrency issues.

Proposed Solution

We can achieve this without any heap allocations (interfaces) by having something like:

type LogRecord struct {
  timestamp time.Time
}

func (lr LogRecord) getTimestamp() time.Time {
  return lr.timestamp
}

func (lr LogRecord) toMutable() MutableLogRecord {
  // Here we can to a clone of the non immutable fields.
}

type MutableLogRecord struct {
  LogRecord
}

func (mlr MutableLogRecord) setTimestamp(t time.Time) {
  mlr.timestamp = t
}

func (mlr MutableLogRecord) asImmutable(t time.Time) LogRecord {
  return mlr.LogRecord
}

[MrAlias]

The specification has explicitly stated that the records passed to Emit need to be mutable so the following processors will see all changes made to them:

• Log record mutations are visible in next registered processors opentelemetry-specification#4067
• Logs: Allow the registered processor to be an independent pipeline opentelemetry-specification#4010

We originally designed the SDK the way you propose, however, it was not compliant with the specification and there was no desire at the specification level to support the change to make it allowed.

[Ali-Alnosairi]

@pellared ,
Does this issue needs to make changes to the specification to support immutable?

[pellared]

@Ali-Alnosairi, as noted before

We originally designed the SDK the way you propose, however, it was not compliant with the specification and there was no desire at the specification level to support the change to make it allowed.

Yes. However, the proposal was already rejected after a few months of discussions. You can read the Specification SIG meeting notes, watch the recording, check the issues and PRs.