In both Ruby 1.8 and 1.9, Ruby code will not cause all threads to block when the CPU is idle. However, poorly coded C libraries that blocked on IO without provi

In both Ruby 1.8 and 1.9, Ruby code will not cause all threads to block when the CPU is idle. However, poorly coded C libraries that blocked on IO without providing Ruby a file descriptor (via rb_thread_select) could cause all threads to block. Those libraries have largely been fixed or replaced (e.g. mysql with mysql2). Ruby 1.9.2 also provides a mechanism for C code to release the GIL if it does not involve any Ruby code, which is used Blythe typecasting code in mysql2, for instance.