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// This file is part of context-allocator. It is subject to the license terms in the COPYRIGHT file found in the top-level directory of this distribution and at https://raw.githubusercontent.com/lemonrock/context-allocator/master/COPYRIGHT. No part of context-allocator, including this file, may be copied, modified, propagated, or distributed except according to the terms contained in the COPYRIGHT file.
// Copyright © 2019 The developers of context-allocator. See the COPYRIGHT file in the top-level directory of this distribution and at https://raw.githubusercontent.com/lemonrock/context-allocator/master/COPYRIGHT.


/// A trait that all such allocators implement.
///
/// Create a new instance using the macro `global_thread_and_coroutine_switchable_allocator`.
pub trait GlobalThreadAndCoroutineSwitchableAllocator: Sync + GlobalAlloc + Alloc + Allocator
{
	/// Type of the coroutine local allocator.
	type CoroutineLocalAllocator: LocalAllocator;

	/// Type of the thread local allocator.
	type ThreadLocalAllocator: LocalAllocator;

	/// Type of the global allocator.
	type GlobalAllocator: Allocator;

	/// Swaps the coroutine local allocator.
	///
	/// Used before calling a coroutine.
	///
	/// Used after calling a coroutine.
	fn replace_coroutine_local_allocator(&self, replacement: Option<Self::CoroutineLocalAllocator>) -> Option<Self::CoroutineLocalAllocator>;

	/// Initializes the thread local allocator.
	fn initialize_thread_local_allocator(&self, thread_local_allocator: Self::ThreadLocalAllocator);

	/// Drops the thread local allocator.
	///
	/// Panics in debug if no thread local allocator has been initialized with `initialize_thread_local_allocator()`.
	///
	/// Could be made hidden by using a destructor with `libc::pthread_key_create()` for an otherwise unused key.
	fn drop_thread_local_allocator(&self);

	/// Save the current allocator in use.
	fn save_current_allocator_in_use(&self) -> CurrentAllocatorInUse;

	/// Restore the current allocator in use.
	fn restore_current_allocator_in_use(&self, restore_to: CurrentAllocatorInUse);

	/// Switch the current allocator in use to coroutine local and execute the callback; restore it after calling the callback unless a panic occurs.
	#[inline(always)]
	fn callback_with_coroutine_local_allocator<R>(&self, callback: impl FnOnce() -> R) -> R
	{
		self.callback_with_different_current_allocator(CurrentAllocatorInUse::CoroutineLocal, callback)
	}

	/// Switch the current allocator in use to thread local and execute the callback; restore it after calling the callback unless a panic occurs.
	#[inline(always)]
	fn callback_with_thread_local_allocator<R>(&self, callback: impl FnOnce() -> R) -> R
	{
		self.callback_with_different_current_allocator(CurrentAllocatorInUse::ThreadLocal, callback)
	}

	/// Switch the current allocator in use to global and execute the callback; restore it after calling the callback unless a panic occurs.
	#[inline(always)]
	fn callback_with_global_allocator<R>(&self, callback: impl FnOnce() -> R) -> R
	{
		self.callback_with_different_current_allocator(CurrentAllocatorInUse::Global, callback)
	}

	/// Switch the current allocator in use and execute the callback; restore it after calling the callback unless a panic occurs.
	#[inline(always)]
	fn callback_with_different_current_allocator<R>(&self, different: CurrentAllocatorInUse, callback: impl FnOnce() -> R) -> R
	{
		let restore_to = self.save_current_allocator_in_use();
		self.restore_current_allocator_in_use(different);
		let result = callback();
		self.restore_current_allocator_in_use(restore_to);
		result
	}

	/// Obtain the current coroutine local allocator, if any.
	fn coroutine_local_allocator(&self) -> Option<&Self::CoroutineLocalAllocator>;

	/// Obtain the coroutine local allocator.
	///
	/// Panics if no coroutine local allocator has been assigned with `replace_coroutine_local_allocator()`.
	#[inline(always)]
	fn coroutine_local_allocator_unchecked(&self) -> &Self::CoroutineLocalAllocator
	{
		self.coroutine_local_allocator().expect("Assign the coroutine local allocator first using `replace_coroutine_local_allocator()`")
	}

	/// Obtain the thread local allocator.
	///
	/// None if no thread local allocator has been initialized with `initialize_thread_local_allocator()`.
	fn thread_local_allocator(&self) -> Option<&Self::ThreadLocalAllocator>;

	/// Obtain the thread local allocator.
	///
	/// Panics if no thread local allocator has been initialized with `initialize_thread_local_allocator()`.
	#[inline(always)]
	fn thread_local_allocator_unchecked(&self) -> &Self::ThreadLocalAllocator
	{
		self.thread_local_allocator().expect("Initialize the thread local allocator first using `initialize_thread_local_allocator()`")
	}

	/// Obtain the global allocator.
	fn global_allocator(&self) -> &Self::GlobalAllocator;
}