/
symbols.go
109 lines (93 loc) · 3.23 KB
/
symbols.go
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// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package runtime
import (
"os"
"reflect"
"sync"
"github.com/apache/beam/sdks/v2/go/pkg/beam/core/util/reflectx"
"github.com/apache/beam/sdks/v2/go/pkg/beam/core/util/symtab"
"github.com/apache/beam/sdks/v2/go/pkg/beam/internal/errors"
)
var (
// Resolver is the accessible symbol resolver the runtime uses to find functions.
Resolver SymbolResolver
cache = make(map[string]interface{})
mu sync.Mutex
)
func init() {
// defer initialization of the default resolver. This way
// the symbol table isn't read in unless strictly necessary.
Resolver = &deferedResolver{initFn: initResolver}
}
type deferedResolver struct {
initFn func() SymbolResolver
r SymbolResolver
init sync.Once
}
func (d *deferedResolver) Sym2Addr(name string) (uintptr, error) {
d.init.Do(func() {
d.r = d.initFn()
})
return d.r.Sym2Addr(name)
}
func initResolver() SymbolResolver {
// First try the Linux location, since it's the most reliable.
if r, err := symtab.New("/proc/self/exe"); err == nil {
return r
}
// For other OS's this works in most cases we need.
if r, err := symtab.New(os.Args[0]); err == nil {
return r
}
return failResolver(false)
}
// SymbolResolver resolves a symbol to an unsafe address.
type SymbolResolver interface {
// Sym2Addr returns the address pointer for a given symbol.
Sym2Addr(string) (uintptr, error)
}
// RegisterFunction allows function registration. It is beneficial for performance
// and is needed for functions -- such as custom coders -- serialized during unit
// tests, where the underlying symbol table is not available. It should be called
// in `init()` only.
func RegisterFunction(fn interface{}) {
if initialized {
panic("Init hooks have already run. Register function during init() instead.")
}
key := reflectx.FunctionName(fn)
// If the function was registered already, the key and value will be the same anyway.
cache[key] = fn
}
// ResolveFunction resolves the runtime value of a given function by symbol name
// and type.
func ResolveFunction(name string, t reflect.Type) (interface{}, error) {
mu.Lock()
defer mu.Unlock()
if val, exists := cache[name]; exists {
return val, nil
}
ptr, err := Resolver.Sym2Addr(name)
if err != nil {
return 0, err
}
val := reflectx.LoadFunction(ptr, t)
cache[name] = val
return val, nil
}
type failResolver bool
func (p failResolver) Sym2Addr(name string) (uintptr, error) {
return 0, errors.Errorf("%v not found. Use runtime.RegisterFunction in unit tests", name)
}