Implementation Issues

• A process have several VMs.
• However there are some "Process Global Information" which should be had each VM
• example: Global variables, working directory, signal

Global Variables Problem

• Problem: Some C codes use gloval variables to store Ruby Objects.
• Because Ruby Objects are belong to each VMs, this is serious problem for MVM on C Ruby.

• Solution: VM local storage C API
• We made VM local storage C API
• rb_vm_specific_ptr(key) returns pointer to VM local storage related to keys
• Keys should be shared by each VMs (Keys are initialized by process level initializer)
• mvm/include/public_object.h includes major global object macros

• Status: Done

 /* mvm/include/public_object.h */
 enum ruby_public_object_vmkey {
   rb_vmkey_mKernel,
 #define rb_mKernel (*rb_vm_specific_ptr(rb_vmkey_mKernel))
   ...
 };

C Extension Problem

• Problem: global variable problem on core interpreter can be solved with above solution, but not on C extensions
• C extension libraries also use global variables

• Solution: two phase initialization
• Current CRuby has initialize mechanism for C extensions: calling Init_foo() for foo library
• MVM needs two phase initialization
• Init_foo() called when foo library loaded at first
• InitVM_foo() called when foo library is required by each VMs.
• Compatibility:
• If foo library has only Init_foo() initializer, foo libraries are used in main VM (first VM in process)

• Status: Doing
• Rewriting loading mechanism

Path Problem

• Problem: working directory is process global information
• Solution: all path related apis are replaced by *at() APIs (openat(), and so on).
• Portability: openat() and other APIs are still new for most of OSs.
• If there is no such APIs, old APIs (open()) with modifying path string.

Signal Problem

• Problem: Signal is delivered to a process, not for VMs.
• Solution: Clarify "out of VM" and "VM internal".
• Call "out of VM" as "Driver" (VM user)
• Call "VM internal" as simply VM
• Signal handler shoud be set by driver
• Driver should deliver a signal information to each VMs with "Driver <-> VM" event communication APIs.

• Status: Done

Other Information

• Problem: there are other information which are process global

• Status: Under review