org.jgroups.blocks
Class GroupRequest
java.lang.Object
org.jgroups.blocks.GroupRequest
- Command, RspCollector
public class GroupRequest
extends java.lang.Object
Sends a message to all members of the group and waits for all responses (or timeout). Returns a
boolean value (success or failure). Results (if any) can be retrieved when done.
The supported transport to send requests is currently either a RequestCorrelator or a generic
Transport. One of them has to be given in the constructor. It will then be used to send a
request. When a message is received by either one, the receiveResponse() of this class has to
be called (this class does not actively receive requests/responses itself). Also, when a view change
or suspicion is received, the methods viewChange() or suspect() of this class have to be called.
When started, an array of responses, correlating to the membership, is created. Each response
is added to the corresponding field in the array. When all fields have been set, the algorithm
terminates.
This algorithm can optionally use a suspicion service (failure detector) to detect (and
exclude from the membership) fauly members. If no suspicion service is available, timeouts
can be used instead (see
execute()
). When done, a list of suspected members
can be retrieved.
Because a channel might deliver requests, and responses to
different requests, the
GroupRequest
class cannot itself receive and process requests/responses from the
channel. A mechanism outside this class has to do this; it has to determine what the responses
are for the message sent by the
execute()
method and call
receiveResponse()
to do so.
Requirements: lossless delivery, e.g. acknowledgment-based message confirmation.
Version:
- Bela Ban
GroupRequest(Message m, Transport transport, Vector members, int rsp_mode)
|
GroupRequest(Message m, Transport transport, Vector members, int rsp_mode, long timeout, int expected_mbrs)
|
GroupRequest(Message m, RequestCorrelator corr, Vector members, int rsp_mode)
|
GroupRequest(Message m, RequestCorrelator corr, Vector members, int rsp_mode, long timeout, int expected_mbrs)
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protected int | determineMajority(int i)
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protected boolean | doExecute(long timeout) - This method runs with rsp_mutex locked (called by
execute() ).
|
boolean | execute() - Sends the message.
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int | getNumSuspects()
|
protected boolean | getResponses()
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RspList | getResults() - Returns the results as a RspList
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Vector | getSuspects()
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boolean | isDone()
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void | receiveResponse(Message m) - Callback (called by RequestCorrelator or Transport).
|
void | reset(Vector mbrs) - This method sets the
membership variable to the value of
members .
|
void | reset(Message m, Vector members, int rsp_mode, long timeout, int expected_rsps)
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void | reset(Message m, int mode, long timeout) - Resets the group request, so it can be reused for another execution.
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void | suspect(Address suspected_member) - Callback (called by RequestCorrelator or Transport).
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String | toString()
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void | viewChange(View new_view) - Any member of 'membership' that is not in the new view is flagged as
SUSPECTED.
|
GET_ABS_MAJORITY
public static final int GET_ABS_MAJORITY
return majority (of all members, may block)
- 4
GET_ALL
public static final int GET_ALL
return all responses
- 2
GET_FIRST
public static final int GET_FIRST
return only first response
- 1
GET_MAJORITY
public static final int GET_MAJORITY
return majority (of all non-faulty members)
- 3
GET_N
public static final int GET_N
return n responses (may block)
- 5
GET_NONE
public static final int GET_NONE
return no response (async call)
- 6
done
protected boolean done
expected_mbrs
protected int expected_mbrs
log
protected static Log log
req_id
protected long req_id
request_msg
protected Message request_msg
rsp_mode
protected int rsp_mode
rsp_mutex
protected Object rsp_mutex
timeout
protected long timeout
GroupRequest
public GroupRequest(Message m,
Transport transport,
Vector members,
int rsp_mode)
GroupRequest
public GroupRequest(Message m,
Transport transport,
Vector members,
int rsp_mode,
long timeout,
int expected_mbrs)
timeout
- Time to wait for responses (ms). A value of <= 0 means wait indefinitely
(e.g. if a suspicion service is available; timeouts are not needed).
GroupRequest
public GroupRequest(Message m,
RequestCorrelator corr,
Vector members,
int rsp_mode)
m
- The message to be sentcorr
- The request correlator to be used. A request correlator sends requests tagged with
a unique ID and notifies the sender when matching responses are received. The
reason GroupRequest
uses it instead of a Transport
is
that multiple requests/responses might be sent/received concurrently.members
- The initial membership. This value reflects the membership to which the request
is sent (and from which potential responses are expected). Is reset by reset().rsp_mode
- How many responses are expected. Can be
GET_ALL
: wait for all responses from non-suspected members.
A suspicion service might warn
us when a member from which a response is outstanding has crashed, so it can
be excluded from the responses. If no suspision service is available, a
timeout can be used (a value of 0 means wait forever). If a timeout of
0 is used, no suspicion service is available and a member from which we
expect a response has crashed, this methods blocks forever !.
GET_FIRST
: wait for the first available response.
GET_MAJORITY
: wait for the majority of all responses. The
majority is re-computed when a member is suspected.
GET_ABS_MAJORITY
: wait for the majority of
all members.
This includes failed members, so it may block if no timeout is specified.
GET_N
: wait for N members.
Return if n is >= membership+suspects.
GET_NONE
: don't wait for any response. Essentially send an
asynchronous message to the group members.
GroupRequest
public GroupRequest(Message m,
RequestCorrelator corr,
Vector members,
int rsp_mode,
long timeout,
int expected_mbrs)
timeout
- Time to wait for responses (ms). A value of <= 0 means wait indefinitely
(e.g. if a suspicion service is available; timeouts are not needed).
determineMajority
protected int determineMajority(int i)
doExecute
protected boolean doExecute(long timeout)
This method runs with rsp_mutex locked (called by execute()
).
execute
public boolean execute()
Sends the message. Returns when n responses have been received, or a
timeout has occurred. n can be the first response, all
responses, or a majority of the responses.
- execute in interface Command
getNumSuspects
public int getNumSuspects()
getResponses
protected boolean getResponses()
getResults
public RspList getResults()
Returns the results as a RspList
getSuspects
public Vector getSuspects()
isDone
public boolean isDone()
receiveResponse
public void receiveResponse(Message m)
Callback (called by RequestCorrelator or Transport).
Adds a response to the response table. When all responses have been received,
execute()
returns.
- receiveResponse in interface RspCollector
reset
public void reset(Vector mbrs)
This method sets the membership
variable to the value of
members
. It requires that the caller already hold the
rsp_mutex
lock.
mbrs
- The new list of members
reset
public void reset(Message m,
Vector members,
int rsp_mode,
long timeout,
int expected_rsps)
reset
public void reset(Message m,
int mode,
long timeout)
Resets the group request, so it can be reused for another execution.
suspect
public void suspect(Address suspected_member)
Callback (called by RequestCorrelator or Transport).
Report to GroupRequest
that a member is reported as faulty (suspected).
This method would probably be called when getting a suspect message from a failure detector
(where available). It is used to exclude faulty members from the response list.
- suspect in interface RspCollector
toString
public String toString()
viewChange
public void viewChange(View new_view)
Any member of 'membership' that is not in the new view is flagged as
SUSPECTED. Any member in the new view that is
not in the
membership (ie, the set of responses expected for the current RPC) will
not be added to it. If we did this we might run into the
following problem:
- Membership is {A,B}
- A sends a synchronous group RPC (which sleeps for 60 secs in the
invocation handler)
- C joins while A waits for responses from A and B
- If this would generate a new view {A,B,C} and if this expanded the
response set to {A,B,C}, A would wait forever on C's response because C
never received the request in the first place, therefore won't send a
response.
- viewChange in interface RspCollector
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