Initial commit

.gitignore

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+cgo-callback
+mylib.o

Makefile

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+GO=go
+
+.PHONY: all
+all: cgo-callback
+
+mylib.o: mylib.c
+
+cgo-callback: mylib.o mylib.h
+	$(GO) build
+
+.PHONY: clean
+clean:
+	rm -f mylib.o cgo-callback

cfuncs.go

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+package main
+
+/*
+#include <stdio.h>
+
+void callOnMeGo_cgo(int n)
+{
+  printf("callOnMeGo_cgo called\n");
+  void callOnMeGo(int);
+  callOnMeGo(n);
+}
+*/
+import "C"

go.mod

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+module git.vtimothy.com/vtimofei/cgo-callback
+
+go 1.18

main.go

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+package main
+
+import (
+  "fmt"
+  "sync"
+  "unsafe"
+)
+
+/*
+#cgo CFLAGS: -I .
+#cgo LDFLAGS: -L .
+
+#include "mylib.h"
+
+void callOnMeGo_cgo(int n);
+*/
+import "C"
+
+//export callOnMeGo
+func callOnMeGo(n int) {
+  printerCallback(n)
+}
+
+type Printer func(int)
+
+var printerCallback Printer
+var printerCallbackLock sync.RWMutex
+
+func usePrinter(p Printer) {
+  printerCallbackLock.Lock()
+  printerCallback = p
+  C.use_printer((C.printer_t)(unsafe.Pointer(C.callOnMeGo_cgo)))
+  printerCallback = nil
+  printerCallbackLock.Unlock()
+}
+
+var myPrinter Printer = Printer(func(n int) {
+  for i := 0; i < n; i++ {
+    fmt.Printf("%d\n", i)
+  }
+})
+
+func main() {
+  usePrinter(myPrinter)
+}

mylib.c

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+#include "mylib.h"
+
+void use_printer(printer_t p)
+{
+  p(14);
+}

mylib.h

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+#ifndef MYLIB_H
+#define MYLIB_H 1
+
+typedef void (*printer_t)(int);
+
+void use_printer(printer_t);
+
+#endif