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