java tink library does not scale with java threads

It seems that java tink library does not scale with java threads. Find attached a small java test program.

Find below test results with one and three threads, running on a unix (redhat) box with 24 vCPUs.

In both cases around 1.000.000 encryption operations are executed every second. The amount of encryption operations is not increasing when using more threads.

java AeadThread encrypt "this is a test" 10000000 1

origtext: this is a test

Thread: 1 for encryption loop: Thu May 25 13:55:22 CEST 2023

Thread: 1 after encryption loop: Thu May 25 13:55:32 CEST 2023

java AeadThread encrypt "this is a test" 10000000 3

origtext: this is a test

Thread: 2 for encryption loop: Thu May 25 13:53:35 CEST 2023

Thread: 3 for encryption loop: Thu May 25 13:53:35 CEST 2023

Thread: 1 for encryption loop: Thu May 25 13:53:35 CEST 2023

Thread: 1 after encryption loop: Thu May 25 13:54:02 CEST 2023

Thread: 2 after encryption loop: Thu May 25 13:54:02 CEST 2023

Thread: 3 after encryption loop: Thu May 25 13:54:02 CEST 2023

AeadThread.zip

Start with the attached AeadThread.zip test program and reproduce the reported encryption timings using one and three threads on the Java implementation. Trace the encryption path to determine why throughput does not increase; done means the cause is identified and the one-versus-three-thread behavior is covered by an appropriate regression or performance test.