Added complete documentation for all C API functions providing exception
handling capabilities in src/exception.c:
## Core C API Functions:
### Exception Protection:
- mrb_protect: executes function under exception protection, equivalent to
Ruby's begin/rescue blocks, catches exceptions and returns them as objects
with error state flag for C code exception handling
### Guaranteed Cleanup:
- mrb_ensure: executes function with guaranteed cleanup, equivalent to Ruby's
begin/ensure blocks, ensures cleanup function always runs regardless of
exceptions, re-raises caught exceptions after cleanup
### Exception Handling:
- mrb_rescue: executes function with StandardError exception handling,
convenience wrapper for common rescue patterns, automatically catches
StandardError and its subclasses
- mrb_rescue_exceptions: executes function with specific exception class
handling, allows selective exception catching based on class hierarchy,
re-raises unmatched exceptions for precise error control
## Helper Components:
### Internal Structures:
- protect_data: helper structure to pass function and data to protection
wrapper, encapsulates function pointer and argument data for safe execution
### Internal Functions:
- protect_body: helper function that wraps user function calls for exception
protection, extracts function and data from protect_data structure and
calls user function with proper parameters
Key features documented:
- Exception protection and propagation control
- Guaranteed cleanup execution (ensure semantics)
- Selective exception class handling with inheritance support
- Integration with mruby's exception system and GC
- C API patterns for robust error handling in extensions
Provides complete coverage of exception handling C API for robust error
management in mruby C extensions and embedded applications, essential
for building reliable C code that integrates with mruby's exception system.
Co-authored-by: Atlassian Rovo Dev
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The purpose is two-fold:
1. to be able to specify a pointer directly when user data is used
When using `mrb_protect()`, it is necessary to allocate objects by `mrb_obj_cptr()` function when using user data.
Adding `mrb_protect_raw()` will make it simpler to reimplement `mrbgems/mruby-error`.
2. to correctly unwind callinfo when an exception is raised from a C function defined as a method (the main topic)
If a method call is made directly under `mrb_protect()` and a C function is called, control is returned from `mrb_protect()` if an exception occurs there.
In this case, callinfo is not restored, so it is out of sync.
Moreover, returning to mruby VM (`mrb_vm_exec()` function) in this state will indicate `ci->pc` of C function which is equal to `NULL`, and subsequent `JUMP` will cause `SIGSEGV`.
Following is an example that actually causes `SIGSEGV`:
- `crash.c`
```c
#include <mruby.h>
#include <mruby/compile.h>
#include <mruby/error.h>
static mrb_value
level1_body(mrb_state *mrb, mrb_value self)
{
return mrb_funcall(mrb, self, "level2", 0);
}
static mrb_value
level1(mrb_state *mrb, mrb_value self)
{
return mrb_protect(mrb, level1_body, self, NULL);
}
static mrb_value
level2(mrb_state *mrb, mrb_value self)
{
mrb_raise(mrb, E_RUNTIME_ERROR, "error!");
return mrb_nil_value();
}
int
main(int argc, char *argv[])
{
mrb_state *mrb = mrb_open();
mrb_define_method(mrb, mrb->object_class, "level1", level1, MRB_ARGS_NONE());
mrb_define_method(mrb, mrb->object_class, "level2", level2, MRB_ARGS_NONE());
mrb_p(mrb, mrb_load_string(mrb, "p level1"));
mrb_close(mrb);
return 0;
}
```
- compile & run
```console
% `bin/mruby-config --cc --cflags --ldflags` crash.c `bin/mruby-config --libs`
% ./a.out
zsh: segmentation fault (core dumped) ./a.out
```
After applying this patch, it will print exception object and exit normally.
The `mrb_protect()`, `mrb_ensure()` and `mrb_rescue_exceptions()` in `mrbgems/mruby-error` have been rewritten using `mrb_protect_raw()`.
Yukihiro "Matz" Matsumoto