Otel.API.Metrics.MeterProvider behaviour (otel v0.2.0)

Global MeterProvider registration and Meter retrieval (OTel metrics/api.md §MeterProvider, Status: Stable, L106-L155).

Holds the process-wide pointer to the installed MeterProvider implementation. When no SDK is installed, all operations resolve to the no-op meter (Otel.API.Metrics.Meter.Noop).

No API-level Meter cache

get_meter/1 does not cache the Meter it returns. Every call delegates to the registered provider's get_meter/2 callback (or returns Noop if none). This avoids a bootstrap race: if an early get_meter/1 is made before the SDK registers, a cached Noop would survive provider installation and silently drop every subsequent measurement.

The spec's "identical for identical parameters" requirement (metrics/api.md L153-L155) is still satisfied because SDK implementations return structurally-equal Meter tuples for equal scopes, and the Noop case is trivially {Noop, []} on every call.

Performance: the API dispatches directly to the provider's get_meter/2 on every call (or returns Noop when no provider is registered). SDK implementations that care about Meter-instance reuse should cache internally on their own get_meter/2 path.

Storage

The global provider pointer lives in :persistent_term. The dispatch pattern ({dispatcher_module, state} tuple

get_meter/2 callback) is shared across Trace, Metrics, and Logs.

opentelemetry-erlang diverges in two places:

Dispatch mechanism — erlang's otel_meter_provider.erl calls gen_server:call/2 directly on every get_meter/1 invocation, wrapping it in catch exit:{noproc, _} -> {otel_meter_noop, []}. We read a persistent_term slot (for the provider) directly — the hot path never hits a process round-trip for provider lookup.
Surface — erlang exposes resource/0,1 and force_flush/0,1 on the MeterProvider module. Those are SDK-level concerns in our design; the API surface is trimmed to spec-required operations.

All functions are safe for concurrent use (spec L1345-L1346).

Public API

Function	Role
`get_meter/0,1`	Application (OTel API MUST) — Get a Meter (L120-L155)
`@callback get_meter/2`	SDK (OTel API MUST) — Dispatch callback (L120-L155)
`get_provider/0`	SDK (installation hook) — access global provider (L110-L112)
`set_provider/1`	SDK (installation hook) — register global provider (L110-L112)

References

OTel Metrics API §MeterProvider: opentelemetry-specification/specification/metrics/api.md L106-L155
OTel Metrics API §Concurrency: opentelemetry-specification/specification/metrics/api.md L1345-L1346
Reference impl (raw gen_server:call): opentelemetry-erlang/apps/opentelemetry_api_experimental/src/otel_meter_provider.erl

Summary

Types

t()

A {dispatcher_module, state} pair.

Callbacks

get_meter(state, instrumentation_scope)

SDK (OTel API MUST) — Dispatch callback invoked by get_meter/1.

Functions

get_meter(instrumentation_scope \\ %Otel.API.InstrumentationScope{})

Application (OTel API MUST) — "Get a Meter" (metrics/api.md L120-L155).

get_provider()

SDK (installation hook) — access the global MeterProvider (metrics/api.md L110-L112).

set_provider(provider)

SDK (installation hook) — register the global MeterProvider (metrics/api.md L110-L112).

Types

t()

@type t() :: {module(), term()}

A {dispatcher_module, state} pair.

The API layer treats the state as opaque; only dispatcher_module knows how to use it. This mirrors Otel.API.Metrics.Meter.t/0 and keeps the API decoupled from SDK internals (GenServer, Registry, etc.).

dispatcher_module MUST implement the Otel.API.Metrics.MeterProvider behaviour.

Callbacks

get_meter(state, instrumentation_scope)

@callback get_meter(
  state :: term(),
  instrumentation_scope :: Otel.API.InstrumentationScope.t()
) :: Otel.API.Metrics.Meter.t()

SDK (OTel API MUST) — Dispatch callback invoked by get_meter/1.

Implementations receive the opaque state they registered via set_provider/1 along with the requested instrumentation scope, and return a Meter. The get_meter/2 shape is the API↔SDK dispatch contract for §"Get a Meter" (metrics/api.md L120-L155).

Functions

get_meter(instrumentation_scope \\ %Otel.API.InstrumentationScope{})

@spec get_meter(instrumentation_scope :: Otel.API.InstrumentationScope.t()) ::
  Otel.API.Metrics.Meter.t()

Application (OTel API MUST) — "Get a Meter" (metrics/api.md L120-L155).

Returns a Meter for the given instrumentation scope. Each call delegates to the registered provider's get_meter/2 callback, or returns the noop meter when no provider is installed — no API-level cache, see the module's "No API-level Meter cache" section.

The full InstrumentationScope struct (name, version, schema_url, attributes — spec L124-L151) is passed to the provider. Spec's "identical for identical parameters" (L153-L155) is satisfied by SDK-side structural equality.

Without arguments, uses a default empty scope.

get_provider()

@spec get_provider() :: t() | nil

SDK (installation hook) — access the global MeterProvider (metrics/api.md L110-L112).

"the API SHOULD provide a way to set/register and access a global default MeterProvider."

Returns the currently registered provider, or nil if none is registered.

set_provider(provider)

@spec set_provider(provider :: t()) :: :ok

SDK (installation hook) — register the global MeterProvider (metrics/api.md L110-L112).

"the API SHOULD provide a way to set/register and access a global default MeterProvider."

Registers the given {module, state} as the global MeterProvider. The SDK MeterProvider calls this from its init/1 with {__MODULE__, server_ref}; module must implement the Otel.API.Metrics.MeterProvider behaviour.

To clear the registration (e.g. in tests), use :persistent_term.erase/1 directly.