Move util services to ntex-util (#89)

* move util services to ntex-util

* update versions

ntex-util/src/services/counter.rs

@@ -0,0 +1,81 @@
+use std::{cell::Cell, rc::Rc, task};
+
+use crate::task::LocalWaker;
+
+/// Simple counter with ability to notify task on reaching specific number
+///
+/// Counter could be cloned, total count is shared across all clones.
+pub struct Counter(Rc<CounterInner>);
+
+struct CounterInner {
+    count: Cell<usize>,
+    capacity: usize,
+    task: LocalWaker,
+}
+
+impl Counter {
+    /// Create `Counter` instance and set max value.
+    pub fn new(capacity: usize) -> Self {
+        Counter(Rc::new(CounterInner {
+            capacity,
+            count: Cell::new(0),
+            task: LocalWaker::new(),
+        }))
+    }
+
+    /// Get counter guard.
+    pub fn get(&self) -> CounterGuard {
+        CounterGuard::new(self.0.clone())
+    }
+
+    /// Check if counter is not at capacity. If counter at capacity
+    /// it registers notification for current task.
+    pub fn available(&self, cx: &mut task::Context<'_>) -> bool {
+        self.0.available(cx)
+    }
+
+    /// Get total number of acquired counts
+    pub fn total(&self) -> usize {
+        self.0.count.get()
+    }
+}
+
+pub struct CounterGuard(Rc<CounterInner>);
+
+impl CounterGuard {
+    fn new(inner: Rc<CounterInner>) -> Self {
+        inner.inc();
+        CounterGuard(inner)
+    }
+}
+
+impl Unpin for CounterGuard {}
+
+impl Drop for CounterGuard {
+    fn drop(&mut self) {
+        self.0.dec();
+    }
+}
+
+impl CounterInner {
+    fn inc(&self) {
+        self.count.set(self.count.get() + 1);
+    }
+
+    fn dec(&self) {
+        let num = self.count.get();
+        self.count.set(num - 1);
+        if num == self.capacity {
+            self.task.wake();
+        }
+    }
+
+    fn available(&self, cx: &mut task::Context<'_>) -> bool {
+        if self.count.get() < self.capacity {
+            true
+        } else {
+            self.task.register(cx.waker());
+            false
+        }
+    }
+}