From 51c15a31043883a976234d80d8b037c34dcd4952 Mon Sep 17 00:00:00 2001
From: Justin Ethier <justin.ethier@gmail.com>
Date: Sun, 9 Aug 2020 18:06:12 -0400
Subject: [PATCH] Initial file

---
 examples/callbacks/complex-scm-call.scm | 47 +++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 examples/callbacks/complex-scm-call.scm

diff --git a/examples/callbacks/complex-scm-call.scm b/examples/callbacks/complex-scm-call.scm
new file mode 100644
index 00000000..064247f4
--- /dev/null
+++ b/examples/callbacks/complex-scm-call.scm
@@ -0,0 +1,47 @@
+(import (scheme base)
+        (scheme write)
+        (srfi 1)
+        (srfi 18))
+
+(include-c-header "sys.h")
+
+(define lock (make-mutex))
+(define *done* #f)
+(define *dummy signal-done) ;; Hack to prevent optimizing out signal-done
+
+(define-c start-c-thread
+  "(void *data, int argc, closure _, object k)"
+  "start_c_thread(data); 
+   return_closcall1(data, k, boolean_t); ")
+
+;; TODO: this does not work right now, it crashes because we are not setup for GC!
+
+;; Signal (wait) that it is done, this is called from C
+(define (signal-done obj)
+ (let ((result 0))
+  (for-each
+    (lambda (n)
+      (set! result (+ result n))
+    )
+    (iota 1000))
+
+  (write `(Called from C set *done* to ,obj))
+  (newline)
+  (mutex-lock! lock)
+  (set! *done* obj)
+  (mutex-unlock! lock)
+  result))
+
+;; More efficient to use a condition var here to signal ready,
+;; but this is just an example
+(define (wait)
+  (thread-sleep! 1)
+  (mutex-lock! lock)
+  (define done *done*)
+  (mutex-unlock! lock)
+  (if done
+      #t
+      (wait)))
+
+(start-c-thread) ;; Spawn a separate C thread since main thread runs Scheme
+(wait) ;; Wait for the signal