CreditBasedFlowControl (Apache Giraph Parent 1.4.0-SNAPSHOT API)

java.lang.Object
- org.apache.giraph.comm.flow_control.CreditBasedFlowControl

All Implemented Interfaces:

FlowControl
```
public class CreditBasedFlowControl
extends Object
implements FlowControl
```
Representation of credit-based flow control policy. With this policy there can be limited number of open requests from any worker x to any other worker y. This number is called 'credit'. Let's denote this number by C{x->y}. This implementation assumes that for a particular worker W, all values of C{x->W} are the same. Let's denote this value by CR_W. CR_W may change due to other reasons (e.g. memory pressure observed in an out-of-core mechanism). However, CR_W is always in range [0, MAX_CR], where MAX_CR is a user-defined constant. Note that MAX_CR should be representable by at most 14 bits. In this implementation, the value of CR_W is announced to other workers along with the ACK response envelope for all ACK response envelope going out of W. Therefore, for non-zero values of CR_W, other workers know the instant value of CR_W, hence they can control the number of open requests they have to W. However, it is possible that W announces 0 as CR_W. In this case, other workers stop opening more requests to W, hence they will not get any new response envelope from W. This means other workers should be notified with a dedicated request to resume sending more requests once CR_W becomes non-zero. In this implementation, once W_CR is announced as 0 to a particular worker U, we keep U in a set, so later on we can send 'resume signal' to U once CR_W becomes non-zero. Sending resume signals are done through a separate thread.

Field Summary

Fields
Modifier and Type	Field and Description
`static IntConfOption`	`MAX_NUM_OF_OPEN_REQUESTS_PER_WORKER` Maximum number of requests we can have per worker without confirmation (i.e.
`static IntConfOption`	`MAX_NUM_OF_UNSENT_REQUESTS` Aggregate number of in-memory unsent requests
`static IntConfOption`	`UNSENT_CACHE_WAIT_INTERVAL` Time interval to wait on unsent requests cahce until we find a spot in it

Constructor Summary

Constructors
Constructor and Description
`CreditBasedFlowControl(ImmutableClassesGiraphConfiguration conf, NettyClient nettyClient, Thread.UncaughtExceptionHandler exceptionHandler)` Constructor

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`int`	`calculateResponse(AckSignalFlag flag, int taskId)` Calculate/Build the response to piggyback with acknowledgement
`AckSignalFlag`	`getAckSignalFlag(int response)` Get the response flag from a response
`int`	`getNumberOfUnsentRequests()`
`void`	`logInfo()` Log the status of the flow control
`void`	`messageAckReceived(int taskId, long requestId, int response)` Notify the flow control policy that an open request is completed.
`void`	`processResumeSignal(int clientId, short credit, long requestId)` Process a resume signal came from a given worker
`void`	`sendRequest(int destTaskId, WritableRequest request)` This method is called by a network client for all requests that should be handled by a remote task.
`void`	`updateCredit(short newCredit)` Update the max credit that is announced to other workers
`void`	`waitAllRequests()` There may be requests in possession of the flow control mechanism, as the mechanism controls whether a task should send a request or not.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - MAX_NUM_OF_OPEN_REQUESTS_PER_WORKER
```
public static final IntConfOption MAX_NUM_OF_OPEN_REQUESTS_PER_WORKER
```
    Maximum number of requests we can have per worker without confirmation (i.e. open requests)
  - MAX_NUM_OF_UNSENT_REQUESTS
```
public static final IntConfOption MAX_NUM_OF_UNSENT_REQUESTS
```
    Aggregate number of in-memory unsent requests
  - UNSENT_CACHE_WAIT_INTERVAL
```
public static final IntConfOption UNSENT_CACHE_WAIT_INTERVAL
```
    Time interval to wait on unsent requests cahce until we find a spot in it
- Constructor Detail
  - CreditBasedFlowControl
```
public CreditBasedFlowControl(ImmutableClassesGiraphConfiguration conf,
                              NettyClient nettyClient,
                              Thread.UncaughtExceptionHandler exceptionHandler)
```
    Constructor
    
    Parameters:
    
    conf - configuration
    
    nettyClient - netty client
    
    exceptionHandler - Exception handler
- Method Detail
  - sendRequest
```
public void sendRequest(int destTaskId,
                        WritableRequest request)
```
    Description copied from interface: FlowControl
    
    This method is called by a network client for all requests that should be handled by a *remote* task. All these requests should be controlled and/or monitored by the flow control policy. The flow control policy may choose to temporarily hold off from sending to a particular remote task and keep the request in some cache for later transfer. A flow control mechanism is free to implement this method as blocking or non-blocking. Note that, a flow-control policy should adhere to exactly-once semantic, meaning it should always send one and only one copy of each request that should be handled by a remote task.
    
    Specified by:
    
    sendRequest in interface FlowControl
    
    Parameters:
    
    destTaskId - id of the worker to send the request to
    
    request - request to send
  - getAckSignalFlag
```
public AckSignalFlag getAckSignalFlag(int response)
```
    Get the response flag from a response
    
    Specified by:
    
    getAckSignalFlag in interface FlowControl
    
    Parameters:
    
    response - response received
    
    Returns:
    
    AckSignalFlag coming with the response
  - calculateResponse
```
public int calculateResponse(AckSignalFlag flag,
                             int taskId)
```
    Description copied from interface: FlowControl
    
    Calculate/Build the response to piggyback with acknowledgement
    
    Specified by:
    
    calculateResponse in interface FlowControl
    
    Parameters:
    
    flag - indicating the status of processing of the request (whether it was a new request or it was a duplicate)
    
    taskId - id of the task the acknowledgement is for
    
    Returns:
    
    the response to piggyback along with the acknowledgement message
  - logInfo
```
public void logInfo()
```
    Description copied from interface: FlowControl
    
    Log the status of the flow control
    
    Specified by:
    
    logInfo in interface FlowControl
  - waitAllRequests
```
public void waitAllRequests()
```
    Description copied from interface: FlowControl
    
    There may be requests in possession of the flow control mechanism, as the mechanism controls whether a task should send a request or not. Calling this method causes the caller to wait until all requests in possession of the flow control mechanism are sent out.
    
    Specified by:
    
    waitAllRequests in interface FlowControl
  - getNumberOfUnsentRequests
```
public int getNumberOfUnsentRequests()
```
    Specified by:
    
    getNumberOfUnsentRequests in interface FlowControl
    
    Returns:
    
    number of unsent requests in possession of the flow control policy
  - messageAckReceived
```
public void messageAckReceived(int taskId,
                               long requestId,
                               int response)
```
    Description copied from interface: FlowControl
    
    Notify the flow control policy that an open request is completed.
    
    Specified by:
    
    messageAckReceived in interface FlowControl
    
    Parameters:
    
    taskId - id of the task to which the open request is completed
    
    requestId - id of the open request which is completed
    
    response - the response heard from the client
  - updateCredit
```
public void updateCredit(short newCredit)
```
    Update the max credit that is announced to other workers
    
    Parameters:
    
    newCredit - new credit
  - processResumeSignal
```
public void processResumeSignal(int clientId,
                                short credit,
                                long requestId)
```
    Process a resume signal came from a given worker
    
    Parameters:
    
    clientId - id of the worker that sent the signal
    
    credit - the credit value sent along with the resume signal
    
    requestId - timestamp (request id) of the resume signal

Class CreditBasedFlowControl

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

MAX_NUM_OF_OPEN_REQUESTS_PER_WORKER

MAX_NUM_OF_UNSENT_REQUESTS

UNSENT_CACHE_WAIT_INTERVAL

Constructor Detail

CreditBasedFlowControl

Method Detail

sendRequest

getAckSignalFlag

calculateResponse

logInfo

waitAllRequests

getNumberOfUnsentRequests

messageAckReceived

updateCredit

processResumeSignal