SubchannelPool

All Known Implementing Classes:

CachedSubchannelPool
```
@NotThreadSafe
interface SubchannelPool
```
Manages life-cycle of Subchannels for GrpclbState.
All methods are run from the ChannelExecutor that the helper uses.

Nested Class Summary

Nested Classes
Modifier and Type Interface Description

static interface SubchannelPool.PooledSubchannelStateListener
Receives state changes for a pooled LoadBalancer.Subchannel.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`clear()`	Shuts down all subchannels in the pool immediately.
`void`	`registerListener(SubchannelPool.PooledSubchannelStateListener listener)`	Registers a listener to received Subchannel status updates.
`void`	`returnSubchannel(LoadBalancer.Subchannel subchannel, ConnectivityStateInfo lastKnownState)`	Puts a `LoadBalancer.Subchannel` back to the pool.
`LoadBalancer.Subchannel`	`takeOrCreateSubchannel(EquivalentAddressGroup eag, Attributes defaultAttributes)`	Takes a `LoadBalancer.Subchannel` from the pool for the given `eag` if there is one available.

- Method Detail
  - registerListener
```
void registerListener(SubchannelPool.PooledSubchannelStateListener listener)
```
    Registers a listener to received Subchannel status updates.
  - takeOrCreateSubchannel
```
LoadBalancer.Subchannel takeOrCreateSubchannel(EquivalentAddressGroup eag,
                                               Attributes defaultAttributes)
```
    Takes a LoadBalancer.Subchannel from the pool for the given eag if there is one available. Otherwise, creates and returns a new Subchannel with the given eag and defaultAttributes.
  - returnSubchannel
```
void returnSubchannel(LoadBalancer.Subchannel subchannel,
                      ConnectivityStateInfo lastKnownState)
```
    Puts a LoadBalancer.Subchannel back to the pool. From this point the Subchannel is owned by the pool, and the caller should stop referencing to this Subchannel.
  - clear
```
void clear()
```
    Shuts down all subchannels in the pool immediately.