How to tune keep-alive connection pool on JAX-RS client

Issue

• How do I tune keep-alive connection pool on JAX-RS client?
• A application is stacked with the following thread dump:

"default task-6" #174 prio=5 os_prio=0 tid=0x0000564f49ef0800 nid=0xd0c waiting on condition [0x00007f9c68a0a000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000f690f828> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
        at org.apache.http.pool.AbstractConnPool.getPoolEntryBlocking(AbstractConnPool.java:393)
        at org.apache.http.pool.AbstractConnPool.access$300(AbstractConnPool.java:70)
        at org.apache.http.pool.AbstractConnPool$2.get(AbstractConnPool.java:253)
        - locked <0x00000000f7cd7e80> (a org.apache.http.pool.AbstractConnPool$2)
        at org.apache.http.pool.AbstractConnPool$2.get(AbstractConnPool.java:198)
        at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.leaseConnection(PoolingHttpClientConnectionManager.java:306)
        at org.apache.http.impl.conn.PoolingHttpClientConnectionManager$1.get(PoolingHttpClientConnectionManager.java:282)
        at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:190)
        at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:186)
        at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
        at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
        at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
        at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
        at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56)
        at org.jboss.resteasy.client.jaxrs.engines.ApacheHttpClient4Engine.invoke(ApacheHttpClient4Engine.java:320)
        at org.jboss.resteasy.client.jaxrs.internal.ClientInvocation.invoke(ClientInvocation.java:443)
        at org.jboss.resteasy.client.jaxrs.internal.ClientInvocation.invoke(ClientInvocation.java:63)
        at org.jboss.resteasy.client.jaxrs.internal.ClientInvocationBuilder.get(ClientInvocationBuilder.java:191)
        at com.redhat.cee.example.resteasy.client.JaxRsClient.sendRequest(JaxRsClient.java:43)
        (omitted)