Class GroupRequest
- All Implemented Interfaces:
RspCollector
,Command
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:
- $Id: GroupRequest.java,v 1.30.2.3 2008/11/17 13:37:59 belaban Exp $
- Author:
- Bela Ban
-
Field Summary
FieldsModifier and TypeFieldDescriptionprotected final RequestCorrelator
protected boolean
protected int
static final int
return majority (of all members, may block)static final int
return all responsesstatic final int
return only first responsestatic final int
return majority (of all non-faulty members)static final int
return n responses (may block)static final int
return no response (async call)protected final Message
protected RspFilter
protected int
protected long
protected Transport
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Constructor Summary
ConstructorsConstructorDescriptionGroupRequest
(Message m, RequestCorrelator corr, Vector<Address> members, int rsp_mode) GroupRequest
(Message m, RequestCorrelator corr, Vector<Address> members, int rsp_mode, long timeout, int expected_mbrs) GroupRequest
(Message m, Transport transport, Vector<Address> members, int rsp_mode) GroupRequest
(Message m, Transport transport, Vector<Address> members, int rsp_mode, long timeout, int expected_mbrs) -
Method Summary
Modifier and TypeMethodDescriptionboolean
execute()
boolean
execute
(boolean use_anycasting) Sends the message.int
Returns the results as a RspListReturns the list of suspected members.boolean
isDone()
void
receiveResponse
(Object response_value, Address sender) Callback (called by RequestCorrelator or Transport).final void
This method sets themembership
variable to the value ofmembers
.void
void
setResponseFilter
(RspFilter filter) void
Callback (called by RequestCorrelator or Transport).toString()
void
viewChange
(View new_view) Any member of 'membership' that is not in the new view is flagged as SUSPECTED.
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Field Details
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GET_FIRST
public static final int GET_FIRSTreturn only first response- See Also:
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GET_ALL
public static final int GET_ALLreturn all responses- See Also:
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GET_MAJORITY
public static final int GET_MAJORITYreturn majority (of all non-faulty members)- See Also:
-
GET_ABS_MAJORITY
public static final int GET_ABS_MAJORITYreturn majority (of all members, may block)- See Also:
-
GET_N
public static final int GET_Nreturn n responses (may block)- See Also:
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GET_NONE
public static final int GET_NONEreturn no response (async call)- See Also:
-
request_msg
-
corr
-
transport
-
rsp_filter
-
rsp_mode
protected int rsp_mode -
done
protected boolean done -
timeout
protected long timeout -
expected_mbrs
protected int expected_mbrs
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Constructor Details
-
GroupRequest
- Parameters:
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 reasonGroupRequest
uses it instead of aTransport
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 beGET_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.
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GroupRequest
public GroupRequest(Message m, RequestCorrelator corr, Vector<Address> members, int rsp_mode, long timeout, int expected_mbrs) - Parameters:
timeout
- Time to wait for responses (ms). A value of invalid input: '<'= 0 means wait indefinitely (e.g. if a suspicion service is available; timeouts are not needed).
-
GroupRequest
-
GroupRequest
public GroupRequest(Message m, Transport transport, Vector<Address> members, int rsp_mode, long timeout, int expected_mbrs) - Parameters:
timeout
- Time to wait for responses (ms). A value of invalid input: '<'= 0 means wait indefinitely (e.g. if a suspicion service is available; timeouts are not needed).
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Method Details
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getCaller
-
setCaller
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setResponseFilter
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execute
-
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.- Throws:
Exception
-
reset
This method sets themembership
variable to the value ofmembers
. It requires that the caller already hold thersp_mutex
lock.- Parameters:
mbrs
- The new list of members
-
receiveResponse
Callback (called by RequestCorrelator or Transport). Adds a response to the response table. When all responses have been received,execute()
returns.- Specified by:
receiveResponse
in interfaceRspCollector
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suspect
Callback (called by RequestCorrelator or Transport). Report toGroupRequest
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.- Specified by:
suspect
in interfaceRspCollector
-
viewChange
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.
- Specified by:
viewChange
in interfaceRspCollector
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getResults
Returns the results as a RspList -
toString
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getNumSuspects
public int getNumSuspects() -
getSuspects
Returns the list of suspected members. An attempt to modify the return value will throw an excxeption -
isDone
public boolean isDone()
-