libgo/go/plugin/plugin.go

   1 // Copyright 2016 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Package plugin implements loading and symbol resolution of Go plugins.
   6 //
   7 // Currently plugins only work on Linux.
   8 //
   9 // A plugin is a Go main package with exported functions and variables that
  10 // has been built with:
  11 //
  12 //      go build -buildmode=plugin
  13 //
  14 // When a plugin is first opened, the init functions of all packages not
  15 // already part of the program are called. The main function is not run.
  16 // A plugin is only initialized once, and cannot be closed.
  17 package plugin
  18
  19 // Plugin is a loaded Go plugin.
  20 type Plugin struct {
  21         pluginpath string
  22         loaded     chan struct{} // closed when loaded
  23         syms       map[string]interface{}
  24 }
  25
  26 // Open opens a Go plugin.
  27 // If a path has already been opened, then the existing *Plugin is returned.
  28 // It is safe for concurrent use by multiple goroutines.
  29 func Open(path string) (*Plugin, error) {
  30         return open(path)
  31 }
  32
  33 // Lookup searches for a symbol named symName in plugin p.
  34 // A symbol is any exported variable or function.
  35 // It reports an error if the symbol is not found.
  36 // It is safe for concurrent use by multiple goroutines.
  37 func (p *Plugin) Lookup(symName string) (Symbol, error) {
  38         return lookup(p, symName)
  39 }
  40
  41 // A Symbol is a pointer to a variable or function.
  42 //
  43 // For example, a plugin defined as
  44 //
  45 //      package main
  46 //
  47 //      // // No C code needed.
  48 //      import "C"
  49 //
  50 //      import "fmt"
  51 //
  52 //      var V int
  53 //
  54 //      func F() { fmt.Printf("Hello, number %d\n", V) }
  55 //
  56 // may be loaded with the Open function and then the exported package
  57 // symbols V and F can be accessed
  58 //
  59 //      p, err := plugin.Open("plugin_name.so")
  60 //      if err != nil {
  61 //              panic(err)
  62 //      }
  63 //      v, err := p.Lookup("V")
  64 //      if err != nil {
  65 //              panic(err)
  66 //      }
  67 //      f, err := p.Lookup("F")
  68 //      if err != nil {
  69 //              panic(err)
  70 //      }
  71 //      *v.(*int) = 7
  72 //      f.(func())() // prints "Hello, number 7"
  73 type Symbol interface{}