Do not use Go pointers containing Go pointers in a CGo call

https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md

1 files changed, 51 insertions, 0 deletions

diff --git a/librsync/pointers.go b/librsync/pointers.go
new file mode 100644
index 0000000..d14f41f
--- /dev/null
+++ b/librsync/pointers.go
@@ -0,0 +1,51 @@
+package librsync
+
+import (
+	"sync"
+)
+
+// pointerMap holds Go *Patcher objects to pass to C.
+// Don't touch this data structure, instead use the storePatcher, getPatcher,
+// and dropPatcher functions.
+var patcherStore = struct {
+	lock  sync.Mutex
+	store map[uintptr]*Patcher
+}{
+	store: make(map[uintptr]*Patcher),
+}
+
+// storePatcher stores the value and returns a reference to it, for use in a CGo
+// call. Use the same reference for dropPatcher. C callbacks can use getPatcher
+// to get the original value.
+func storePatcher(patcher *Patcher, id uintptr) {
+	patcherStore.lock.Lock()
+	defer patcherStore.lock.Unlock()
+
+	if _, ok := patcherStore.store[id]; ok {
+		// Just to be on the safe side.
+		panic("pointer already stored")
+	}
+	patcherStore.store[id] = patcher
+}
+
+// getPatcher returns the value for the reference id. It returns nil if there
+// is no such reference.
+func getPatcher(id uintptr) *Patcher {
+	patcherStore.lock.Lock()
+	defer patcherStore.lock.Unlock()
+
+	return patcherStore.store[id]
+}
+
+// dropPatcher unreferences the value so the garbage collector can free it's
+// memory.
+func dropPatcher(id uintptr) {
+	patcherStore.lock.Lock()
+	defer patcherStore.lock.Unlock()
+
+	if _, ok := patcherStore.store[id]; !ok {
+		panic("pointer not stored")
+	}
+
+	delete(patcherStore.store, id)
+}