Add more precise description

specification/metrics/api.md

@@ -360,9 +360,9 @@ instrumentation libraries from capturing metrics by the same name.
 
 ### Shutdown
 
-Exporting pending metrics.
+Shuts down the provider.
 
-The `Shutdown` API MAY be implemented by invoking `Shutdown` within internal processors.
+The `Shutdown` API provides a way for provider to do any cleanup required.
 
 ### Global Meter provider
 

specification/trace/api.md

@@ -94,7 +94,7 @@ number of `TracerProvider` instances.
 The `TracerProvider` MUST provide the following functions:
 
 - Get a `Tracer`
-- Shutdown the provider (exporting pending spans)
+- Shuts down the provider
 
 That `Tracer()` API MUST accept the following parameters:
 
@@ -126,7 +126,7 @@ the tracer could, for example, do a look-up with its name+version in a map in
 the `TracerProvider`, or the `TracerProvider` could maintain a registry of all
 returned `Tracer`s and actively update their configuration if it changes.
 
-The `Shutdown` API MAY be implemented by invoking `Shutdown` within internal processors.
+The `Shutdown` API provides a way for provider to do any cleanup required.
 
 ## Tracing Context Utilities
 

specification/trace/sdk.md

@@ -5,7 +5,7 @@
 <summary>Table of Contents</summary>
 
 * [Sampling](#sampling)
-* [Tracer Creation](#tracer-creation)
+* [Tracer Provider](#tracer-provider)
 * [Additional Span Interfaces](#additional-span-interfaces)
 * [Span Processor](#span-processor)
 * [Span Exporter](#span-exporter)
@@ -180,7 +180,9 @@ Optional parameters:
 |present|false|true|`localParentSampled()`|
 |present|false|false|`localParentNotSampled()`|
 
-## Tracer Creation
+## Tracer Provider
+
+### Tracer Creation
 
 New `Tracer` instances are always created through a `TracerProvider` (see
 [API](api.md#tracerprovider)). The `name` and `version` arguments
@@ -201,6 +203,22 @@ Note: Implementation-wise, this could mean that `Tracer` instances have a
 reference to their `TracerProvider` and access configuration only via this
 reference.
 
+### Shutdown
+
+`Shutdown` SHOULD be called only once for each `TracerProvider` instance. After
+the call to `Shutdown`, subsequent calls to get `Tracer` are not allowed. SDKs
+SHOULD ignore these calls gracefully, if possible.
+
+`Shutdown` SHOULD provide a way to let the caller know whether it succeeded,
+failed or timed out.
+
+`Shutdown` SHOULD complete or abort within some timeout. `Shutdown` can be
+implemented as a blocking API or an asynchronous API which notifies the caller
+via a callback or an event. Language library authors can decide if they want to
+make the shutdown timeout configurable.
+
+The `Shutdown` API MAY be implemented by invoking `Shutdown` within internal processors.
+
 ## Additional Span Interfaces
 
 The [API-level definition for Span's interface](api.md#span-operations)