}
				cg := s.Doc
				if cg == nil && len(decl.Specs) == 1 {
					cg = decl.Doc
				}
				if cg != nil {
					if strings.ContainsAny(abspath, "\r\n") {
						// This should have been checked when the file path was first resolved,
						// but we double check here just to be sure.
						fatalf("internal error: ParseGo: abspath contains unexpected newline character: %q", abspath)
					}

called by C code may take a Go pointer but it must preserve the property
that the Go memory to which it points (and the Go memory to which that
memory points, and so on) is pinned.

These rules are checked dynamically at runtime. The checking is
controlled by the cgocheck setting of the GODEBUG environment
variable. The default setting is GODEBUG=cgocheck=1, which implements

	g()
}
</pre>

<p>
it can happen that <code>g</code> prints <code>2</code> and then <code>0</code>.
</p>

<p>
This fact invalidates a few common idioms.
</p>

<p>
Double-checked locking is an attempt to avoid the overhead of synchronization.
For example, the <code>twoprint</code> program might be
incorrectly written as:
</p>

<pre>
var a string
var done bool

func setup() {

		if output[0] == "" {
			// spurious blank caused by Split on "\n"
			output = output[1:]
			continue
		}
		t.Errorf("unexpected output: %q", output[0])
		output = output[1:]
	}

	// Checked printing.
	// Now check machine code layout.

	top := pList.Firstpc
	var text *obj.LSym
	ok = true
	ctxt.DiagFunc = func(format string, args ...interface{}) {
		t.Errorf(format, args...)
		ok = false