Ruby

• vm.c: support variable VM/Machine stack sizes.
  Specified by the following environment variaables:
  • RUBY_THREAD_VM_STACK_SIZE: vm stack size used at thread creation.
    default: 128KB (32bit CPU) or 256KB (64bit CPU).
  • RUBY_THREAD_MACHINE_STACK_SIZE: machine stack size used at thread
    creation. default: 512KB or 1024KB.
  • RUBY_FIBER_VM_STACK_SIZE: vm stack size used at fiber creation.
    default: 64KB or 128KB.
  • RUBY_FIBER_MACHINE_STACK_SIZE: machine stack size used at fiber
    creation. default: 256KB or 256KB.
    This values are specified at launched timing. You can not change
    these values at running time.
    Environ variables are only hints because:
  • They are aligned to 4KB.
  • They have minimum values (depend on OSs).
  • Machine stack settings are ignored by some OSs.
    Default values especially fiber stack sizes are increased.
    This change affect Fiber's behavior:
    (1) You can run more complex program on a Fiber.
    (2) You can not make many (thousands) Fibers because of
    lack of address space (on 32bit CPU).
    If (2) bothers you,
    (a) Use 64bit CPU with big memory, or
    (b) Specify RUBY_FIBER_(VM|MACHINE)_STACK_SIZE correctly.
    You need to choose correct stack size carefully. These values
    are completely rely on systems (OS/compiler and so on).
• vm_core.h (rb_vm_t::default_params): add to record above settings.
• vm.c (RubyVM::DEFAULT_PARAMS): add new constant to see
  above setting.
• thread_pthread.c: support RUBY_THREAD_MACHINE_STACK_SIZE.
• cont.c: support RUBY_FIBER_(VM|MACHINE)_STACK_SIZE.
• test/ruby/test_fiber.rb: add tests for above.
• test/ruby/test_thread.rb: ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38478 b2dd03c8-39d4-4d8f-98ff-823fe69b080e