Fix connection pool bug which can cause delays in obtaining a connection

[andreachild]

It has been observed in some environments that integration tests such as GraphBinaryGroovyRemoteFeatureTest can encounter 16 second delays between test executions. Investigation shows this can occur if one thread is attempting to obtain a connection and another thread is creating or releasing a connection at the same time. It is possible for the thread releasing or creating a connection to signal the hasAvailableConnection condition after the other thread has determined there are no available connections but before calling await on the condition. Thus the thread obtaining the connection will wait for default timeout of 16 seconds before attempting to retrieve a connection again, causing the observed delays.

This fix involves locking the waitLock before obtaining and potentially calling await for an available connection which prevents other threads from signalling the hasAvailableConnection before other threads call await. The fix was tested by observing integration test execution on environments which previously produced the 16 second delays and also by executing ProfilingApplication. The results of ProfilingApplication did not demonstrate any degradation of average requests per second.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 78.11%. Comparing base (cfd6889) to head (65e6f1f).
Report is 200 commits behind head on master.

Files with missing lines	Patch %	Lines
...pache/tinkerpop/gremlin/driver/ConnectionPool.java	71.42%	2 Missing and 2 partials ⚠️
...rpop/gremlin/driver/util/ProfilingApplication.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3079      +/-   ##
============================================
+ Coverage     77.87%   78.11%   +0.24%     
- Complexity    13578    13969     +391     
============================================
  Files          1015     1019       +4     
  Lines         59308    60036     +728     
  Branches       6835     6971     +136     
============================================
+ Hits          46184    46896     +712     
+ Misses        10817    10816       -1     
- Partials       2307     2324      +17     

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[Cole-Greer]

VOTE +1

[kenhuuu]

VOTE +1

[xiazcy]

VOTE +1