src/pkg/runtime/iface.goc

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package runtime
#include "runtime.h"
#include "arch_GOARCH.h"
#include "type.h"
#include "typekind.h"
#include "malloc.h"
#include "../../cmd/ld/textflag.h"

extern	Itab*	runtime·hash[1009];
extern	Lock	runtime·ifaceLock;

// TODO: delete this when no longer used (ifaceE2I2 is all that's left)
static Itab*
itab(InterfaceType *inter, Type *type, int32 canfail)
{
	int32 locked;
	int32 ni;
	Method *t, *et;
	IMethod *i, *ei;
	uint32 h;
	String *iname, *ipkgPath;
	Itab *m;
	UncommonType *x;
	Type *itype;
	Eface err;

	if(inter->mhdr.len == 0)
		runtime·throw("internal error - misuse of itab");

	locked = 0;

	// easy case
	x = type->x;
	if(x == nil) {
		if(canfail)
			return nil;
		iname = inter->m[0].name;
		goto throw;
	}

	// compiler has provided some good hash codes for us.
	h = inter->typ.hash;
	h += 17 * type->hash;
	// TODO(rsc): h += 23 * x->mhash ?
	h %= nelem(runtime·hash);

	// look twice - once without lock, once with.
	// common case will be no lock contention.
	for(locked=0; locked<2; locked++) {
		if(locked)
			runtime·lock(&runtime·ifaceLock);
		for(m=runtime·atomicloadp(&runtime·hash[h]); m!=nil; m=m->link) {
			if(m->inter == inter && m->type == type) {
				if(m->bad) {
					m = nil;
					if(!canfail) {
						// this can only happen if the conversion
						// was already done once using the , ok form
						// and we have a cached negative result.
						// the cached result doesn't record which
						// interface function was missing, so jump
						// down to the interface check, which will
						// do more work but give a better error.
						goto search;
					}
				}
				if(locked)
					runtime·unlock(&runtime·ifaceLock);
				return m;
			}
		}
	}

	ni = inter->mhdr.len;
	m = runtime·persistentalloc(sizeof(*m) + ni*sizeof m->fun[0], 0, &mstats.other_sys);
	m->inter = inter;
	m->type = type;

search:
	// both inter and type have method sorted by name,
	// and interface names are unique,
	// so can iterate over both in lock step;
	// the loop is O(ni+nt) not O(ni*nt).
	i = inter->m;
	ei = i + inter->mhdr.len;
	t = x->m;
	et = t + x->mhdr.len;
	for(; i < ei; i++) {
		itype = i->type;
		iname = i->name;
		ipkgPath = i->pkgPath;
		for(;; t++) {
			if(t >= et) {
				if(!canfail) {
				throw:
					// didn't find method
					runtime·newTypeAssertionError(
						nil, type->string, inter->typ.string,
						iname, &err);
					if(locked)
						runtime·unlock(&runtime·ifaceLock);
					runtime·panic(err);
					return nil;	// not reached
				}
				m->bad = 1;
				goto out;
			}
			if(t->mtyp == itype && t->name == iname && t->pkgPath == ipkgPath)
				break;
		}
		if(m)
			m->fun[i - inter->m] = t->ifn;
	}

out:
	if(!locked)
		runtime·panicstring("invalid itab locking");
	m->link = runtime·hash[h];
	runtime·atomicstorep(&runtime·hash[h], m);
	runtime·unlock(&runtime·ifaceLock);
	if(m->bad)
		return nil;
	return m;
}

// call the callback for every itab that is currently allocated.
void
runtime·iterate_itabs(void (*callback)(Itab*))
{
	int32 i;
	Itab *tab;

	for(i = 0; i < nelem(runtime·hash); i++) {
		for(tab = runtime·hash[i]; tab != nil; tab = tab->link) {
			callback(tab);
		}
	}
}

// Still in C because it is called from C for finalizers.  This will
// get converted to Go in a separate CL.  This is the last user of
// the C version of itab().
bool
runtime·ifaceE2I2(InterfaceType *inter, Eface e, Iface *ret)
{
	ret->tab = itab(inter, e.type, 1);
	if(ret->tab == nil)
		return false;
	ret->data = e.data;
	return true;
}