/* * 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 libnbd // 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 }