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/*
* This file is part of the libvirt-go project
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*
* Copyright (c) 2013 Alex Zorin
* Copyright (C) 2016 Red Hat, Inc.
*
*/
package libvirt
// Helpers functions to register a Go callback function to a C
// function. For a simple example, look at how SetErrorFunc works in
// error.go.
//
// - Create a struct that will contain at least the Go callback to
// invoke (errorContext).
//
// - Create an exported Golang function whose job will be to retrieve
// the context and execute the callback in it
// (connErrCallback). Such a function should receive a callback ID
// and will use it to retrive the context.
//
// - Create a CGO function similar to the above function but with the
// appropriate signature to be registered as a callback in C code
// (connErrCallbackHelper). Notably, it will have a void* argument
// that should be cast to long to retrieve the callback ID. It
// should be just a thin wrapper to transform the opaque argument to
// a callback ID.
//
// - Create a CGO function which will be a wrapper around the C
// function to register the callback (virConnSetErrorFuncWrapper). Its
// only role is to transform a callback ID (long) to an opaque (void*)
// and call the C function.
//
// - When setting up a callback (SetErrorFunc), register the struct from first step
// with registerCallbackId and invoke the CGO function from the
// previous step with the appropriate ID.
//
// - When unregistering the callback, don't forget to call freecallbackId.
//
// If you need to associate some additional data with the connection,
// look at saveConnectionData, getConnectionData and
// releaseConnectionData.
import "C"
import (
"sync"
)
const firstGoCallbackId int = 100 // help catch some additional errors during test
var goCallbackLock sync.RWMutex
var goCallbacks = make(map[int]interface{})
var nextGoCallbackId int = firstGoCallbackId
//export freeCallbackId
func freeCallbackId(goCallbackId int) {
goCallbackLock.Lock()
delete(goCallbacks, goCallbackId)
goCallbackLock.Unlock()
}
func getCallbackId(goCallbackId int) interface{} {
goCallbackLock.RLock()
ctx := goCallbacks[goCallbackId]
goCallbackLock.RUnlock()
if ctx == nil {
// If this happens there must be a bug in libvirt
panic("Callback arrived after freeCallbackId was called")
}
return ctx
}
func registerCallbackId(ctx interface{}) int {
goCallbackLock.Lock()
goCallBackId := nextGoCallbackId
nextGoCallbackId++
for goCallbacks[nextGoCallbackId] != nil {
nextGoCallbackId++
}
goCallbacks[goCallBackId] = ctx
goCallbackLock.Unlock()
return goCallBackId
}
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