[Feature #19443]
It's not uncommon for database client and similar network libraries
to protect themselves from Process.fork by regularly checking Process.pid
Until recently most libc would cache `getpid()` so this was a cheap
check to make.
However as of glibc version 2.25 the PID cache is removed and calls to
`getpid()` always invoke the actual system call which significantly degrades
the performance of existing applications.
The reason glibc removed the cache is that some libraries were bypassing
`fork(2)` by issuing system calls themselves, causing stale cache issues.
That isn't a concern for Ruby as bypassing MRI's primitive for forking
would render the VM unusable, so we can safely cache the PID.
A variable modified in `EXEC_TAG` block should be `volatile`.
```
ractor.c: In function 'ractor_try_yield':
ractor.c:1251:97: warning: argument 'obj' might be clobbered by 'longjmp' or 'vfork' [-Wclobbered]
1251 | ractor_try_yield(rb_execution_context_t *ec, rb_ractor_t *cr, struct rb_ractor_queue *ts, VALUE obj, VALUE move, bool exc, bool is_will)
| ~~~~~~^~~
```
[Bug #19536]
When objects are moved between size pools, their frozen status is lost
in the shape. This will cause the frozen check to be bypassed when there
is an inline cache. For example, the following script should raise a
FrozenError, but doesn't on Ruby 3.2 and master.
class A
def add_ivars
@a = @b = @c = @d = 1
end
def set_a
@a = 10
end
end
a = A.new
a.add_ivars
a.freeze
b = A.new
b.add_ivars
b.set_a # Set the inline cache in set_a
GC.verify_compaction_references(expand_heap: true, toward: :empty)
a.set_a
This assert would've caught a bug I wrote while developing
ruby/ruby#7443 so I figured it would be good to commit it
as it could be helpful in the future.
