It seems that some users want to wrap rather large chunk of code
with wasm_runtime_begin_blocking_op/wasm_runtime_end_blocking_op.
If the wrapped code happens to have a call to
e.g. wasm_runtime_spawn_exec_env, WASM_SUSPEND_FLAG_BLOCKING is
inherited to the child exec_env and it may cause unexpected behaviors.
Send a signal whose handler is no-op to a blocking thread to wake up
the blocking syscall with either EINTR equivalent or partial success.
Unlike the approach taken in the `dev/interrupt_block_insn` branch (that is,
signal + longjmp similarly to `OS_ENABLE_HW_BOUND_CHECK`), this PR
does not use longjmp because:
* longjmp from signal handler doesn't work on nuttx
refer to https://github.com/apache/nuttx/issues/10326
* the singal+longjmp approach may be too difficult for average programmers
who might implement host functions to deal with
See also https://github.com/bytecodealliance/wasm-micro-runtime/issues/1910
We have observed a significant performance degradation after merging
https://github.com/bytecodealliance/wasm-micro-runtime/pull/1991
Instead of protecting suspend flags with a mutex, we implement the flags
as atomic variable and only use mutex when atomics are not available
on a given platform.
