Initial reorg.

This is largely the same as #305, but updated for the current tree.

crates/wasi-c/sandboxed-system-primitives/src/refcount.h

@@ -0,0 +1,47 @@
+// Part of the Wasmtime Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://github.com/CraneStation/wasmtime/blob/master/LICENSE for license information.
+//
+// Significant parts of this file are derived from cloudabi-utils. See
+// https://github.com/CraneStation/wasmtime/blob/master/lib/wasi/sandboxed-system-primitives/src/LICENSE
+// for license information.
+//
+// The upstream file contains the following copyright notice:
+//
+// Copyright (c) 2016 Nuxi, https://nuxi.nl/
+
+#ifndef REFCOUNT_H
+#define REFCOUNT_H
+
+#include <assert.h>
+#include <stdatomic.h>
+#include <stdbool.h>
+
+#include "locking.h"
+
+// Simple reference counter.
+struct LOCKABLE refcount {
+  atomic_uint count;
+};
+
+#define PRODUCES(...) LOCKS_SHARED(__VA_ARGS__) NO_LOCK_ANALYSIS
+#define CONSUMES(...) UNLOCKS(__VA_ARGS__) NO_LOCK_ANALYSIS
+
+// Initialize the reference counter.
+static void refcount_init(struct refcount *r, unsigned int count) PRODUCES(*r) {
+  atomic_init(&r->count, count);
+}
+
+// Increment the reference counter.
+static inline void refcount_acquire(struct refcount *r) PRODUCES(*r) {
+  atomic_fetch_add_explicit(&r->count, 1, memory_order_acquire);
+}
+
+// Decrement the reference counter, returning whether the reference
+// dropped to zero.
+static inline bool refcount_release(struct refcount *r) CONSUMES(*r) {
+  int old = atomic_fetch_sub_explicit(&r->count, 1, memory_order_release);
+  assert(old != 0 && "Reference count becoming negative");
+  return old == 1;
+}
+
+#endif