$ docker run --rm --cpus=1 --memory=1g --entrypoint java flags-demo:jdk27 -XX:+PrintFlagsFinal -version | grep -E "ParallelGCThreads|ConcGCThreads|ActiveProcessorCount"
$ docker run --rm --cpus=1 --memory=1g --entrypoint java flags-demo:jdk27 -XX:ActiveProcessorCount=8 -XX:+PrintFlagsFinal -version | grep -E "ParallelGCThreads|ConcGCThreads|ActiveProcessorCount"

=== ActiveProcessorCount lying to the JVM: 1 real CPU, told there are 8 ===
--- JDK27, --cpus=1, no override (correct) ---
      int ActiveProcessorCount                     = -1                                        {product} {default}
     uint ConcGCThreads                            = 1                                         {product} {ergonomic}
     uint ParallelGCThreads                        = 1                                         {product} {default}

--- JDK27, --cpus=1, -XX:ActiveProcessorCount=8 (lying) ---
      int ActiveProcessorCount                     = 8                                         {product} {command line}
     uint ConcGCThreads                            = 2                                         {product} {ergonomic}
     uint ParallelGCThreads                        = 8                                         {product} {default}