Fiber switching was disabled during destructor execution due to conflicts
with the garbage collector. This unfortunately introduces a function color
problem: destructors can not call functions that may switch Fibers.
In this change we update the GC so that Fiber switching during GC is safe. In
turn we allow Fiber switching during destrutor execution.
The GC executes destructors in a dedicated Fiber. If a destructor suspends, the
Fiber is owned by userland and a new dedicated Fiber is created to execute the
remaining destructors. Destructor suspension results in a resurection of the
object, which is handled as usual: The object is not considered garbage anymore,
but may be collected in a later run.
When the GC is executed in the main context (not in a Fiber), then destructors
are executed in the main context as well because there is no risk of conflicting
with GC in this case (main context can not suspend).
Fixes GH-11389
Closes GH-13460
According to @nikic:
> The current guideline for use of bool and zend_result in php-src is
> that bool is an appropriate return value for "is" or "has" style
> functions, which return a yes/no answer. zend_result is an
> appropriate return value for functions that perform some operation
> that may succeed or fail.
Closes GH-10622.
The variable size of zend_fiber_stack results in the offset of other fields to be variable, which causes compatiblity issues with extensions when php-src is compiled with ASan enabled. This solution was prefered over moving the stack field to be the last member, as inclusion of ZEND_FIBER_CONTEXT_FIELDS into other structs may still result in field offset errors.
The definition of zend_fiber_stack was removed from the header to hide it from the ABI.
Renamed prior_pointer and prior_size to asan_pointer and asan_size to reflect their current use.
Changed context flags type to uint8_t.
Renamed valgrind stack id field to valgrind_stack_id and fixed the type to unsigned int.
This additional internal fiber API creates and manipulates a Fiber object, allowing any internal function to start, resume, or suspend a fiber. The existing zend_fiber_context API allows custom C-based fiber creation using the bundled switching context, but does not interact with the PHP VM. This API behaves the same as calling Fiber object methods from user code, switching EGs, and triggering the fiber switch observer. In general, the Fiber object methods call these new API methods.
This removes switching to main for fatal errors in fibers in favor of catching any zend_bailout in a fiber and calling zend_bailout again after switching to the previous fiber or {main}.
This is needed by both fibers and opcache (and GH-6903 also uses it),
so make it a common structure that can be used by any functionality
storing warnings/errors.
