Token Management

· If the existing tokens can be revoked, the File Exporter revokes them and grants those requested. When its tokens are revoked, a client such as the Cache Manager flushes cached data for which the tokens applied, writing any modified data back to the File Server machine. (Information about token revocation follows this list.)

· If the existing tokens cannot be revoked, the File Exporter either places the request in a queue, to be serviced as soon as possible, or refuses to grant the requested tokens outright. The client dictates the File Exporter's response to this situation when it requests the tokens.

In general, if a client's existing tokens conflict with those requested by another client, the File Exporter attempts to revoke the existing tokens to grant the request. Many factors influence the File Exporter's ability to revoke a client's tokens. The File Exporter can usually revoke some types of tokens, but clients can refuse to relinquish other types of tokens in various situations. In addition, lifetimes that the File Exporter assigns to the tokens it grants and to the clients to which it grants them also affect its ability to revoke tokens, as follows:

Token Lifetime
Specifies the length of time for which a token is valid. All tokens have a fixed token lifetime. Once its lifetime has elapsed, a token expires. The File Exporter needs to revoke only valid tokens. Because expired tokens are no longer valid, the File Exporter does not need to revoke them; it can simply grant new tokens as if the expired tokens did not exist. A client can contact the File Exporter to request that its tokens' lifetimes be extended before they expire.

Host Lifetime
Indicates the length of time for which the File Exporter considers a client to be alive. Each client that has tokens from the File Exporter has a host lifetime within which it must contact the File Exporter to let it know that it is still alive, thus renewing its host lifetime. The File Exporter needs the client's permission to revoke tokens that are held by the client as long as the client's host lifetime has not expired.

Host RPC Lifetime
Defines the length of time for which the File Exporter guarantees to attempt to make an RPC to a client before the File Exporter revokes its tokens. If the client responds to the RPC (thus renewing its host lifetime), the File Exporter cannot revoke the client's tokens without the client's permission. If the client fails to respond to the RPC but its host lifetime has not expired, the File Exporter cannot revoke the client's tokens; if the client fails to respond and its host lifetime has expired, the File Exporter can revoke any tokens the client holds without attempting to contact it further. The File Exporter can revoke the tokens of any client whose host RPC lifetime has expired without contacting the client; the client needs to either reclaim its tokens or request new ones as necessary.

Each File Exporter defines the lengths of its clients' host lifetimes and host RPC lifetimes, so a client can have different lifetimes for different File Exporters. For any File Exporter, however, a client's host RPC lifetime must be equal to or greater than its host lifetime. (By default, both lifetimes are only a few minutes in length.)

The following general rules govern the File Exporter's revocation of valid tokens held by a client:

1. If the client's host lifetime has not expired, the File Exporter tries to contact the client; the File Exporter must have the client's permission to revoke its tokens.

2. If the client's host lifetime has expired but its host RPC lifetime has not, the File Exporter tries to contact the client one time. If the client responds, the File Exporter cannot revoke the client's tokens without its permission; otherwise, the File Exporter can revoke any tokens held by the client without contacting it further.

3. If the client's host RPC lifetime has expired, the File Exporter can revoke the client's tokens without contacting it.