[Issue 242][pulsar-client-go] feature: add send timeout

[lifepuzzlefun]

Fixes #242

Motivation

add send timeout

Modifications

1. ProduceOptions
   add SendTimeout and SendTimeoutCheckInterval in ProducerOptions

2. BlockingQueue
   unexported BlockingQueue.Iterator
   and add methods to avoid race condition.
   BlockingQueue.IterateIfNonEmpty and BlockingQueue.PollIfSatisfy

3. partitionProducer
   add a ticker to check if pendingItem in pendingQueue has expired.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

add some tiny test in producer_test.go

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): no
• The public API: no
• The schema: no
• The default values of configurations: no
• The wire protocol: no

Documentation

• Does this pull request introduce a new feature? yes
• If yes, how is the feature documented? (not applicable / docs / GoDocs / not documented)
• If a feature is not applicable for documentation, explain why?
• If a feature is not documented yet in this PR, please create a followup issue for adding the documentation

[merlimat]

The Send() is already taking a Context object. If the context has a timeout, it will be used.

[merlimat]

I think the correct fix for #242 would be to also check the context before attempting to publish the message.

[lifepuzzlefun]

yeah, i think it should be, but when user pass different context with different sendtimeout to Send and SendAsync , this will introduce a lot of complicity. the message is send as batch. and each message in batch with different timeout

[lifepuzzlefun]

i'm confused about the above use case, need some guide on the real popuse of passing an context here. and where do you prefer to check the context？ just before send or both before send and time
wait for response.

[yarthur1]

I hope that both before send and time wait for response should check timeout.I don't want to wait send func always,because I meet this situation where pulsar broker has something wrong and send func always wait @

[lifepuzzlefun]

closed and goto #252