Why `fiber::mutex` yields in `try_lock` even after acquiring the lock successfully?

[rodman10]

Recently I'm reading the source code of fiber::mutex, I noticed thatfiber::mutex will yield in try_lock no matter whether holding the lock or not? What's the considerations behind it, and can we just return immediately after lock? Thanks in advance.

fiber/src/mutex.cpp

Lines 43 to 60 in 238487b

	bool
	mutex::try_lock() {
	context * active_ctx = context::active();
	detail::spinlock_lock lk{ wait_queue_splk_ };
	if ( BOOST_UNLIKELY( active_ctx == owner_) ) {
	throw lock_error{
	std::make_error_code( std::errc::resource_deadlock_would_occur),
	"boost fiber: a deadlock is detected" };
	}
	if ( nullptr == owner_) {
	owner_ = active_ctx;
	}
	lk.unlock();
	// let other fiber release the lock
	active_ctx->yield();
	return active_ctx == owner_;
	}