From f07e4dae3c5cb608b4f0b9db57d1562d2125243b Mon Sep 17 00:00:00 2001 From: Michael Anthony Knyszek Date: Wed, 19 May 2021 15:46:44 +0000 Subject: [PATCH] syscall: document NewCallback and NewCallbackCDecl limitations Currently NewCallback and NewCallbackCDecl may only be called a limited number of times in a single Go process, but this property of the API is not documented. This change fixes that, but does not document the precise limit to avoid making that limit part of the API, leaving us open to increasing or decreasing the limit in the future as needed. Although the API avoids documenting a limit, it does guarantee a minimum callback count so users can rely on at least some amount of callbacks working. Updates #46184. Change-Id: I5129bf5fe301efff73ac112ba1f207ab32058833 Reviewed-on: https://go-review.googlesource.com/c/go/+/321133 Trust: Michael Knyszek Reviewed-by: Ian Lance Taylor --- src/syscall/syscall_windows.go | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/src/syscall/syscall_windows.go b/src/syscall/syscall_windows.go index fa0b5d959af..fc734effbbe 100644 --- a/src/syscall/syscall_windows.go +++ b/src/syscall/syscall_windows.go @@ -174,6 +174,9 @@ func compileCallback(fn interface{}, cleanstack bool) uintptr // NewCallback converts a Go function to a function pointer conforming to the stdcall calling convention. // This is useful when interoperating with Windows code requiring callbacks. // The argument is expected to be a function with one uintptr-sized result. The function must not have arguments with size larger than the size of uintptr. +// Only a limited number of callbacks may be created in a single Go process, and any memory allocated +// for these callbacks is never released. +// Between NewCallback and NewCallbackCDecl, at least 1024 callbacks can always be created. func NewCallback(fn interface{}) uintptr { return compileCallback(fn, true) } @@ -181,6 +184,9 @@ func NewCallback(fn interface{}) uintptr { // NewCallbackCDecl converts a Go function to a function pointer conforming to the cdecl calling convention. // This is useful when interoperating with Windows code requiring callbacks. // The argument is expected to be a function with one uintptr-sized result. The function must not have arguments with size larger than the size of uintptr. +// Only a limited number of callbacks may be created in a single Go process, and any memory allocated +// for these callbacks is never released. +// Between NewCallback and NewCallbackCDecl, at least 1024 callbacks can always be created. func NewCallbackCDecl(fn interface{}) uintptr { return compileCallback(fn, false) }