JIT compilation can happen at any time. The runtime wants to create a native version of a previously interpreted snippet of code when it is called frequently enough to warrant this.

The article also describes W^X functionality, which means a region of memory is either executable (x)or writable. On macOS 14.4 violating this either-or condition results in a signal that can not be handled by the process.

The article doesnt say anything about the JVM accessing other processes memory though.