Senders fix, do not use static thrift factory

[pavolloffay]

When I was using multiple tracers in one process HttpSender was sending corrupted data.

[codecov-io]

Codecov Report

Merging #233 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #233      +/-   ##
============================================
- Coverage     81.89%   81.87%   -0.02%     
+ Complexity      525      524       -1     
============================================
  Files            87       87              
  Lines          2005     2003       -2     
  Branches        236      236              
============================================
- Hits           1642     1640       -2     
  Misses          263      263              
  Partials        100      100

Impacted Files	Coverage Δ	Complexity Δ
...ain/java/com/uber/jaeger/senders/ThriftSender.java	73.46% <ø> (ø)	10 <0> (ø)	⬇️
...c/main/java/com/uber/jaeger/senders/UdpSender.java	69.23% <100%> (-2.2%)	4 <1> (-1)
.../main/java/com/uber/jaeger/senders/HttpSender.java	90.32% <100%> (-0.31%)	7 <2> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 912bfdb...a58b860. Read the comment docs.

[vprithvi]

Change looks good. Do you think it’s worth having a test case with concurrent tracers?

[pavolloffay]

We would have to emulate deserialization on the server size.

Could we get it in and if necessary write test in separate PR? It's blocking my work spark-depenencies PR https://github.com/pavolloffay/spark-dependencies/pull/1.

[pavolloffay]

Once this is merged. Could you please do micro release? (I don't have rights and @jpkrohling will be here on Wednesday)

[vprithvi]

Yeah, we can write a test as a separate PR. I'll merge and release

[yurishkuro]

@pavolloffay are you saying the factory is not thread safe?

[pavolloffay]

I haven't digged very deep. I will write a test later and look more closely.

[vprithvi]

The serializer isn't threadsafe, but looking at https://github.com/apache/thrift/blob/master/lib/java/src/org/apache/thrift/protocol/TBinaryProtocol.java#L85 it seems that we should be able to continue having the factory as static.