Prototype Request¶

This type of request is made by sending an event of type io.s4.message.PrototypeRequest. These are targeted at the prototype of PEs of a particular type. One copy of the request is sent to every S4 node in the cluster, and each node typically responds with one response message. So if the S4 cluster has N nodes, the caller should expect up to N response events. However, due to the non-guaranteed nature of UDP, not all messages may be delivered.

Single PE Request¶

This type of request is encoded as an io.s4.message.SinglePERequest event. It is targeted at a single PE and can be used to access propertes of the PE with a public getter method. One request results in at most one response.

Response¶

The response for a request, consisting of a list of queries, is an object with the following properties:

Example 1¶

In this example, we will query the prototype of the joiner (SentenceJoinPE) in the speech02 application.

The JSON representation of the corresponding prototype request is:

{
  "query": ["count"],
  "rinfo": {"id":123}
}

The driver repository contains a script to send requests and receive responses at $S4_IMAGE/s4-driver/scripts/request.py:

import io.s4.client.driver
import pprint;
import sys;

mode = {'readMode': 'private', 'writeMode': 'enabled'};

stream = sys.argv[1];
clazz = sys.argv[2];

d = io.s4.client.driver.Driver('localhost', 2334)

#Enable debug messages
d.setDebug(True);

d.initialize();
d.connect(mode);

print "Sending all requests..."

for req in sys.stdin.readlines():
    d.send(stream, clazz, req);

print "Waiting 5 sec to collect all responses..."
responses = d.recvAll(5);
print "\n"*4

print "Done. Results:"
print pprint.pformat(responses, indent=4);

d.disconnect();

Use this as follows:

python $S4_IMAGE/s4-driver/scripts/request.py '#sentenceJoinPE' \
'io.s4.message.PrototypeRequest' < $S4_IMAGE/s4-example-testinput/proto-query

The resulting session starts with something like the following:

<<[0]
>>[117]{"protocol":{"name":"generic-json","versionMajor":1,"versionMinor":0},"uuid":"c7c9df6e-754a-41c5-aa8b-a373dcf2b4a6"}

Initialized. uuid: c7c9df6e-754a-41c5-aa8b-a373dcf2b4a6
<<[95]{"writeMode": "enabled", "readMode": "private", "uuid":
"c7c9df6e-754a-41c5-aa8b-a373dcf2b4a6"}
>>[15]{"status":"ok"}
Connected
Sending all requests...

See the protocol in action. In particular, the response object (pretty formatted) is:

{
  "result": {"count":11},
  "exception":{},
  "request":{
              "query":["count"],
              "rinfo":{
                        "requesterUUID":"c7c9df6e-754a-41c5-aa8b-a373dcf2b4a6",
                        "id":123,
                        "stream":"@client-adapter",
                        "partition":0
                      }
            }
}

The result indicates that there are 11 joiner PEs. These correspond to the 11 sentences in the test input file.

$ wc -l ${SOURCE_BASE}/examples/testinput/speech.in
11  ...

Also notice that there is infomation in the rinfo field, which was not present in the request that we sent. These are added by the adapter.

Example 2¶

Example request to a single PE from $S4_IMAGE/s4-example-testinput/proto-query

{"target":["16000000"],"query":["$outputClassName"],"rinfo":{"id":0,"stream":"@client"}}
{"target":["*"],"query":["$outputClassName"],"rinfo":{"id":1,"stream":"@client"}}

Send this to the S4 cluster using:

python $S4_IMAGE/s4-driver/scripts/request.py '#sentenceJoinPE' \
'io.s4.message.SinglePERequest' < $S4_IMAGE/s4-example-testinput/pe-query

The input contains two queries. The two corresponding responses (pretty-formatted and truncated) are:

{
  "result":{"$outputClassName":"io.s4.example.speech01.Sentence"},
  "exception":{},
  "request":{
              "target":["16000000"],
              "query":["$outputClassName"],
              "rinfo":{
                        "requesterUUID":"cf2d1726-2919-4eb1-85fc-7e420908587e",
                        "id":0,
                        "stream":"@client-adapter",
                        "partition":0
                      }
            }
}

{
  "result":{},
  "exception":{"$outputClassName":"java.lang.Exception: Null Target"},
  "request":{
              "target":["*"],
              "query":["$outputClassName"],
              "rinfo":{
                        "requesterUUID":"cf2d1726-2919-4eb1-85fc-7e420908587e",
                        "id":1,
                        "stream":"@client-adapter",
                        "partition":0
                      }
            }
}

The first response (request id 0) was sent to a PE, and that PE responded with its output class name as requested. The second query (request id 1) was targeted at a joiner corresponding to the key value "*". No such PE exists, so an exception was thrown.