[fix][client] Add initialization for the OpSendMsg

[RobertIndie]

Motivation

Some parameters in OpSendMsg are not specified with initialized values.

These initial values are all relied upon by other codes. Such as here:

pulsar/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ProducerImpl.java

Lines 1409 to 1422 in eec46dd

	//firstSentAt and lastSentAt maybe -1, it means that the message didn't flush to channel.
	String errMsg = String.format(
	"%s : createdAt %s seconds ago, firstSentAt %s seconds ago, lastSentAt %s seconds ago, "
	+ "retryCount %s",
	te.getMessage(),
	RelativeTimeUtil.nsToSeconds(ns - this.createdAt),
	RelativeTimeUtil.nsToSeconds(this.firstSentAt <= 0
	? this.firstSentAt
	: ns - this.firstSentAt),
	RelativeTimeUtil.nsToSeconds(this.lastSentAt <= 0
	? this.lastSentAt
	: ns - this.lastSentAt),
	retryCount
	);

Modifications

• Add the initialization for the OpSendMsg.

Documentation

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[BewareMyPower]

Please explain what's the affect of these fields without initial values.

[RobertIndie]

Please explain what's the affect of these fields without initial values.

I have explained it in the PR description. Is there something unclear?

[BewareMyPower]

In addition, adding initial values to a recyclable class is dangerous. For a recyclable class, we should make constructors private and only expose some factory methods and set the value in these factory methods.

The reason is that if the object was reused from the pool, the initial value should be what was set in recycle() method.

For example,

@Data
class RecyclableInteger {
    private static final Recycler<RecyclableInteger> RECYCLER = new Recycler<RecyclableInteger>() {
        @Override
        protected RecyclableInteger newObject(Handle<RecyclableInteger> handle) {
            return new RecyclableInteger(handle);
        }
    };

    private final Recycler.Handle<RecyclableInteger> handle;
    private int x = 100; // initial value: 100

    private RecyclableInteger(Recycler.Handle<RecyclableInteger> handle) {
        this.handle = handle;
    }

    public static RecyclableInteger create() {
        return RECYCLER.get(); // retrieve an object without modifying the value of `x`
    }

    public void recycle() {
        this.x = 0; // recycled value: 0
        handle.recycle(this);
    }
}

        RecyclableInteger i = RecyclableInteger.create();
        System.out.println(i.getX()); // 100 as we expected
        i.recycle();
        i = RecyclableInteger.create();
        System.out.println(i.getX()); // 0, which is unexpected

[BewareMyPower]

I have explained it in the PR description. Is there something unclear?

Sorry at the time I replied, the PR description was not updated. Then, please see my another comment.

[BewareMyPower]

The best practice might be adding an initialize() method to a recyclable class and calling this method at the beginning of each factory method, like:

    private void initialize() {
        x = 100;
    }

    public static RecyclableInteger create() {
        final RecyclableInteger i = RECYCLER.get();
        i.initialize();
        return i;
    }

[RobertIndie]

In addition, adding initial values to a recyclable class is dangerous. For a recyclable class, we should make constructors private and only expose some factory methods and set the value in these factory methods.

The reason is that if the object was reused from the pool, the initial value should be what was set in recycle() method.

Before this PR, there is already an inconsistent issue in the OpSendMsg. The value of the OpSendMsg just initialized is not the same as the OpSendMsg just being recycled. This PR is to fix this inconsistency. I was wondering if we could have the recyle method call some kind of initialization method so we don't need to maintain the same initialization value in two places.

[BewareMyPower]

if we could have the recyle method call some kind of initialization method so we don't need to maintain the same initialization value in two places.

Yes.

[RobertIndie]

@BewareMyPower Hi, I have added the initialization for the OpSendMsg, PTAL again. Thanks.

[nodece]

LGTM