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 // A plugin is a Go main package with exported functions and variables that
   8 // has been built with:
   9 //
  10 //      go build -buildmode=plugin
  11 //
  12 // When a plugin is first opened, the init functions of all packages not
  13 // already part of the program are called. The main function is not run.
  14 // A plugin is only initialized once, and cannot be closed.
  15 //
  16 // Currently plugins are only supported on Linux, FreeBSD, and macOS.
  17 // Please report any issues.
  18 package plugin
  19
  20 // Plugin is a loaded Go plugin.
  21 type Plugin struct {
  22         pluginpath string
  23         err        string        // set if plugin failed to load
  24         loaded     chan struct{} // closed when loaded
  25         syms       map[string]any
  26 }
  27
  28 // Open opens a Go plugin.
  29 // If a path has already been opened, then the existing *Plugin is returned.
  30 // It is safe for concurrent use by multiple goroutines.
  31 func Open(path string) (*Plugin, error) {
  32         return open(path)
  33 }
  34
  35 // Lookup searches for a symbol named symName in plugin p.
  36 // A symbol is any exported variable or function.
  37 // It reports an error if the symbol is not found.
  38 // It is safe for concurrent use by multiple goroutines.
  39 func (p *Plugin) Lookup(symName string) (Symbol, error) {
  40         return lookup(p, symName)
  41 }
  42
  43 // A Symbol is a pointer to a variable or function.
  44 //
  45 // For example, a plugin defined as
  46 //
  47 //      package main
  48 //
  49 //      import "fmt"
  50 //
  51 //      var V int
  52 //
  53 //      func F() { fmt.Printf("Hello, number %d\n", V) }
  54 //
  55 // may be loaded with the Open function and then the exported package
  56 // symbols V and F can be accessed
  57 //
  58 //      p, err := plugin.Open("plugin_name.so")
  59 //      if err != nil {
  60 //              panic(err)
  61 //      }
  62 //      v, err := p.Lookup("V")
  63 //      if err != nil {
  64 //              panic(err)
  65 //      }
  66 //      f, err := p.Lookup("F")
  67 //      if err != nil {
  68 //              panic(err)
  69 //      }
  70 //      *v.(*int) = 7
  71 //      f.(func())() // prints "Hello, number 7"
  72 type Symbol any