The patch assumes that `struct REnv::cxt` only performs checks with the `OP_BREAK` and `OP_RETURN_BLK` instructions, and does not reference the entity.
Therefore, by changing to a weak reference, it is possible to collect fibers that are no longer directly referenced while in the suspended state.
However, we need to detach the living env objects that remain in the call stack of the fiber.
So, in effect, it involves a revert of following commits.
- commit a3365d8b3f
- commit 57ffa1c150
Examples of the effects of change are shown below.
Note that it was built with `rake MRUBY_CONFIG=host-debug`.
```ruby
f = Fiber.new { (x, y, z) = "X", "Y", "Z"; Fiber.yield -> { [x, y, z] } }
g = f.resume
GC.start
p ObjectSpace.memsize_of_all
# => 59532
g.call
# => ["X", "Y", "Z"]
f = nil
GC.start
ObjectSpace.memsize_of_all
# BEFORE => 59532
# AFTER => 58044
g.call
# => ["X", "Y", "Z"]
```
`mrb_env_unshare()` calls `mrb_realloc_simple()` and follows `mrb_full_gc()` to avoid an infinite loop where `mrb_env_unshare()` is called again.
This does not occur at this time, but may occur in subsequent patches.
For reference, the flexible array was introduced by commit 3ab2f9371e (#2997).
Subsequently changed for compatibility with C++ by commit 24939723d7 (#5596).
The `MRB_TT_BACKTRACE` object has been added for the purpose.
Previously, "use-after-free" could occur because the reference count in `backtrace_location::irep` was not incremented.
fixed#6160
The method introduced by #5979 causes a fault by swapping classes.
```console
% bin/mruby -e 'Method = Proc; p Object.method(:inspect)'
zsh: segmentation fault (core dumped) bin/mruby -e 'Method = Proc; p Object.method(:inspect)'
```
After applying this patch, a `TypeError` exception will be raised.
```console
% bin/mruby -e 'Method = Proc; p Object.method(:inspect)'
trace (most recent call last):
[1] -e:1
-e:1:in method: allocation failure of Proc (TypeError)
```
However, if the `mrb_vtype` is the same object, the same care must still be taken as before.
```console
% bin/mruby -e 'Method = Binding; p method(:puts).eval("12345")'
trace (most recent call last):
[1] -e:1
-e:1:in eval: wrong argument type nil (expected Proc) (TypeError)
```
It is now possible to specify return destination directly.
This allows callinfo to distinguish between calls to the same proc object.
At the same time, the `Kernel#catch` method is adjusted.
By removing the previously required double lambda object, the REnv object is no longer created as well.
Since `Env` objects are shared by Blocks/Procs in the same context,
making multiple aliases in one context screws up with alias names.
New implementation uses alias bodies (Procs) to refer new names.
As a side effect, `__callee__` stop working correctly for aliases.
To fix this `__callee__` problem, we need to keep alias method names in
`callinfo`, which consumes more memory. We are wondering that is worth
the compatibility.
Since when env objects reference the context, we no longer need to
unshare (stack reallocate) env objects. Currently all env objects
referenced from fibers are already recycled, so we removed unnecessary
code altogether.
dearblue