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syscall/js: improve documentation of js.FuncOf

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The existing documentation is improved to be more
explicit about the lifecycle and its consequences.

Fixes #34324

Change-Id: I9969afc69f6eeb7812c11fe821a842794df5aa5b
GitHub-Last-Rev: 246a499166
GitHub-Pull-Request: golang/go#34551
Reviewed-on: https://go-review.googlesource.com/c/go/+/197458
Reviewed-by: Richard Musiol <neelance@gmail.com>
This commit is contained in:
Torben Schinke 2020-03-01 20:07:46 +00:00 committed by Richard Musiol
parent e44cda3aa9
commit a4f7b0879c
1 changed files with 14 additions and 9 deletions
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23
src/syscall/js/func.go
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@ -22,17 +22,22 @@ type Func struct {
id uint32
}
// FuncOf returns a wrapped function.
// FuncOf returns a function to be used by JavaScript.
//
// Invoking the JavaScript function will synchronously call the Go function fn with the value of JavaScript's
// "this" keyword and the arguments of the invocation.
// The return value of the invocation is the result of the Go function mapped back to JavaScript according to ValueOf.
// The Go function fn is called with the value of JavaScript's "this" keyword and the
// arguments of the invocation. The return value of the invocation is
// the result of the Go function mapped back to JavaScript according to ValueOf.
//
// A wrapped function triggered during a call from Go to JavaScript gets executed on the same goroutine.
// A wrapped function triggered by JavaScript's event loop gets executed on an extra goroutine.
// Blocking operations in the wrapped function will block the event loop.
// As a consequence, if one wrapped function blocks, other wrapped funcs will not be processed.
// A blocking function should therefore explicitly start a new goroutine.
// Invoking the wrapped Go function from JavaScript will
// pause the event loop and spawn a new goroutine.
// Other wrapped functions which are triggered during a call from Go to JavaScript
// get executed on the same goroutine.
//
// As a consequence, if one wrapped function blocks, JavaScript's event loop
// is blocked until that function returns. Hence, calling any async JavaScript
// API, which requires the event loop, like fetch (http.Client), will cause an
// immediate deadlock. Therefore a blocking function should explicitly start a
// new goroutine.
//
// Func.Release must be called to free up resources when the function will not be used any more.
func FuncOf(fn func(this Value, args []Value) interface{}) Func {