Check connection has not been closed at first while checking the validity of connection

[pvinokurov]

In the current implementation of PoolBase#isConnectionDead(isConnectionAlive) setNetworkTimeout() is called firstly to check the connection validity: PoolBase#L151

In many JDBC drivers, calling Connection#setNetworkTimeout throws SqlException in the case when a connection is closed. For example, Postgres JDBC driver throws PSQLException("This connection has been closed.") by calling setNetworkTimeout() PgConnection#L1622 PgConnection.java#L883

The behavior of isConnectionDead() method looks odd because in the case of apriori closed connection it causes an exception and logging warning. If a connection is not valid by the result of Connection.isValid method the warning is not logged. The warning message could be confusing due to the indirect relation between maxLifeTime parameter and closed connections.

The proposal is to check that connection is closed before calling setNetworkTimeout thereby not causing the exception and logging the warning.

[codecov[bot]]

Codecov Report

Merging #1890 (e7ffb6a) into dev (ed2da5f) will decrease coverage by 0.52%. The diff coverage is 100.00%.

@@             Coverage Diff              @@
##                dev    #1890      +/-   ##
============================================
- Coverage     70.75%   70.22%   -0.53%     
+ Complexity      575      574       -1     
============================================
  Files            26       26              
  Lines          2171     2173       +2     
  Branches        311      311              
============================================
- Hits           1536     1526      -10     
- Misses          484      497      +13     
+ Partials        151      150       -1     

Impacted Files	Coverage Δ
src/main/java/com/zaxxer/hikari/pool/PoolBase.java	68.36% <100.00%> (-3.80%)	:arrow_down:
...ain/java/com/zaxxer/hikari/util/ConcurrentBag.java	74.46% <0.00%> (-1.07%)	:arrow_down:

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[lfbayer]

Brett has explained the reason why not to solve this problem in this way in an earlier comment here: https://github.com/brettwooldridge/HikariCP/issues/1212#issuecomment-417404421