Add environmental module

substrate/environmental/Cargo.toml

+[package]
+name = "environmental"
+version = "0.1.0"
+authors = ["Parity Technologies <admin@parity.io>"]

substrate/environmental/src/lib.rs

+// Copyright 2017 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+use std::cell::RefCell;
+use std::thread::LocalKey;
+
+pub fn using_environment<'a, T: 'a, S, F: FnOnce()>(
+	global: &'static LocalKey<RefCell<*mut S>>,
+	protected: &'a mut T,
+	f: F
+) {
+	global.with(|r| *r.borrow_mut() = protected as *mut T as *mut S);
+	f();
+	global.with(|r| *r.borrow_mut() = 0 as *mut S);
+}
+
+pub fn with_environment<'r, S, T: 'r, F: FnOnce(&'r mut T)>(
+	global: &'static LocalKey<RefCell<*mut S>>,
+	mutator: F,
+) {
+	global.with(|r| {
+		let br = r.borrow_mut();
+		if *br != 0 as *mut S {
+			// safe because it's only non-zero when it in with_environment, which
+			// is holding on to the underlying reference safely
+			unsafe {
+				mutator(&mut *(*br as *mut S as *mut T));
+			}
+		}
+	});
+}
+
+#[macro_export]
+macro_rules! decl_environment {
+	($name:ident : $t:ty) => {
+		thread_local! {
+			static $name: std::cell::RefCell<*mut $t> = std::cell::RefCell::new(0 as *mut $t);
+		}
+	}
+}
+
+#[macro_export]
+macro_rules! declare_generic_environment {
+	($name:ident : $t:tt) => {
+		mod $name {
+			use super::*;
+
+			decl_environment!(GLOBAL: $t<'static> );
+
+			pub fn using<'a: 'b, 'b, F: FnOnce(), T: 'a>(protected: &'b mut T, f: F) {
+				$crate::using_environment(&GLOBAL, protected, f);
+			}
+
+			pub fn with<F: for<'r, 't: 'r> FnOnce(&'r mut $t<'t>)>(f: F) {
+				let dummy = ();
+				with_closed(f, &dummy);
+			}
+
+			fn with_closed<'d: 't, 't: 'r, 'r, F: FnOnce(&'r mut $t<'t>)>(
+				f: F,
+				_dummy: &'d (),
+			) {
+				$crate::with_environment(&GLOBAL, f);
+			}
+		}
+	}
+}
+
+#[macro_export]
+macro_rules! declare_simple_environment {
+	($name:ident : $t:tt) => {
+		mod $name {
+			use super::*;
+
+			decl_environment!(GLOBAL: $t );
+
+			pub fn using<'a: 'b, 'b, F: FnOnce(), T: 'a>(protected: &'b mut T, f: F) {
+				$crate::using_environment(&GLOBAL, protected, f);
+			}
+
+			pub fn with<F: for<'r> FnOnce(&'r mut $t)>(f: F) {
+				let dummy = ();
+				with_closed(f, &dummy);
+			}
+
+			fn with_closed<'d: 'r, 'r, F: FnOnce(&'r mut $t)>(
+				f: F,
+				_dummy: &'d (),
+			) {
+				$crate::with_environment(&GLOBAL, f);
+			}
+		}
+	}
+}