add ffi/unsafe/global and switch openssl to use it

Continues the move away from using the FFI to access unsafe Racket
functionality.

pkgs/racket-doc/scribblings/foreign/derived.scrbl

@@ -14,6 +14,7 @@
 @include-section["custodian.scrbl"]
 @include-section["atomic.scrbl"]
 @include-section["try-atomic.scrbl"]
+@include-section["global.scrbl"]
 @include-section["objc.scrbl"]
 @include-section["ns.scrbl"]
 @include-section["com.scrbl"]

pkgs/racket-doc/scribblings/foreign/global.scrbl

@@ -0,0 +1,31 @@
+#lang scribble/doc
+@(require "utils.rkt"
+          (for-label ffi/unsafe/global))
+
+@title{Process-Wide Registration}
+
+@defmodule[ffi/unsafe/global]{The
+@racketmodname[ffi/unsafe/global] library provides a utility
+registering information that spans all places in the Racket
+process.}
+
+@history[#:added "6.9.0.5"]
+
+@defproc[(register-process-global [key bytes?]
+                                  [val cpointer?])
+         cpointer?]{
+
+Gets or sets a value in a process-global table (i.e., shared across
+multiple places, if any).
+
+If @racket[val] is @racket[#f], the current mapping for @racket[key]
+is reported.
+
+If @racket[val] is not @racket[#f], and no value has been installed
+for @racket[key], then the value is installed and @racket[#f] is
+returned. If a value has already been installed, then no new value is
+installed and the old value is returned. The given @racket[val] must
+not refer to garbage-collected memory.
+
+This function is intended for infrequent use with a small number of
+keys.}

pkgs/racket-doc/scribblings/inside/custodians.scrbl

@@ -1,5 +1,6 @@
 #lang scribble/doc
-@(require "utils.rkt")
+@(require "utils.rkt"
+          (for-label ffi/unsafe/custodian))
 
 @title{Custodians}
 
@@ -64,7 +65,10 @@ most one custodian.
 
 If @var{m} (or the current custodian if @var{m} is @cpp{NULL}) is shut
 down, then @var{f} is called immediately, and the result is
-@cpp{NULL}.}
+@cpp{NULL}.
+
+See also @racket[register-custodian-shutdown] from
+@racketmodname[ffi/unsafe/custodian].}
 
 @function[(Scheme_Custodian_Reference* scheme_add_managed_close_on_exit
            [Scheme_Custodian* m]
@@ -94,7 +98,10 @@ Checks whether @var{m} is already shut down, and raises an error if
 
 Removes @var{o} from the management of its custodian. The @var{mref}
  argument must be a value returned by @cpp{scheme_add_managed} or
- @cpp{NULL}.}
+ @cpp{NULL}.
+
+See also @racket[unregister-custodian-shutdown] from
+@racketmodname[ffi/unsafe/custodian].}
 
 @function[(void scheme_close_managed
            [Scheme_Custodian* m])]{

pkgs/racket-doc/scribblings/inside/misc.scrbl

@@ -1,5 +1,6 @@
 #lang scribble/doc
-@(require "utils.rkt")
+@(require "utils.rkt"
+          (for-label ffi/unsafe/global))
 
 @title{Miscellaneous Utilities}
 
@@ -392,7 +393,10 @@ value is returned. The given @var{val} must not refer to garbage-collected
 memory.
 
 This function is intended for infrequent use with a small number of
-keys.}
+keys.
+
+See also @racket[register-process-global] from
+@racketmodname[ffi/unsafe/global].}
 
 @function[(void* scheme_jit_find_code_end
                  [void* p])]{

racket/collects/ffi/unsafe/global.rkt

@@ -0,0 +1,8 @@
+#lang racket/base
+(require (only-in '#%unsafe
+                  unsafe-register-process-global))
+
+(provide register-process-global)
+
+(define (register-process-global bstr val)
+  (unsafe-register-process-global bstr val))

racket/collects/openssl/mzssl.rkt

@@ -28,6 +28,7 @@ TO DO:
          ffi/unsafe/define
          ffi/unsafe/atomic
          ffi/unsafe/alloc
+         ffi/unsafe/global
          ffi/file
          ffi/unsafe/custodian
          racket/list
@@ -1687,10 +1688,6 @@ TO DO:
 (define ssl-available? (and libssl #t))
 
 
-(define scheme_register_process_global
-  (and ssl-available?
-       (get-ffi-obj 'scheme_register_process_global #f (_fun _string _pointer -> _pointer))))
-
 (when ssl-available?
   ;; Make sure only one place tries to initialize OpenSSL,
   ;; and wait in case some other place is currently initializing
@@ -1698,18 +1695,18 @@ TO DO:
   (begin
     (start-atomic)
     (let* ([done (cast 1 _scheme _pointer)]
-           [v (scheme_register_process_global "OpenSSL-support-initializing" done)])
+           [v (register-process-global #"OpenSSL-support-initializing" done)])
       (if v
           ;; Some other place is initializing:
           (begin
             (end-atomic)
             (let loop ()
-              (unless (scheme_register_process_global "OpenSSL-support-initialized" #f)
+              (unless (register-process-global #"OpenSSL-support-initialized" #f)
                 (sleep 0.01) ;; busy wait! --- this should be rare
                 (loop))))
           ;; This place must initialize:
           (begin
             (SSL_library_init)
             (SSL_load_error_strings)
-            (scheme_register_process_global "OpenSSL-support-initialized" done)
+            (register-process-global #"OpenSSL-support-initialized" done)
             (end-atomic))))))