Commit 89bd29a9058eabf23c735761c49809bb63a68842 | zig

author	Erik Arvstedt <erik.arvstedt@gmail.com> 2023-06-12 22:21:31+02:00
committer	Erik Arvstedt <erik.arvstedt@gmail.com> 2023-06-13 09:48:51+02:00
log	89bd29a9058eabf23c735761c49809bb63a68842
tree	ff4248f657d3a71f335f0648dc8df947ef90e253
parent	5d3c8f4913884a4503e9f183e471b6090bb5bc92

arena_allocator/reset: avoid zero-capacity allocations

1. When the arena is already empty, resetting with `retain_capacity` no longer
   results in allocating a buffer with zero capacity.
   This behavior was previously intended by the `(current_capacity == 0)` check,
   but wasn't correctly implemented.

2. Resetting with `.{ .retain_with_limit = 0 }` is now equivalent to
   `free_all` and a new buffer with zero capacity is no longer created.
   This is a useful side-effect of the above fixes.

1 files changed, 7 insertions(+), 10 deletions(-)

lib
- std
  - heap
    arena_allocator.zig

lib/std/heap/arena_allocator.zig+7-10

...	...	@@ -108,21 +108,18 @@ pub const ArenaAllocator = struct {
108	108	// Thus, only the first hand full of calls to reset() will actually need to iterate the linked
109	109	// list, all future calls are just taking the first node, and only resetting the `end_index`
110	110	// value.
111		const current_capacity = if (mode != .free_all)
112		@sizeOf(BufNode) + self.queryCapacity() // we need at least space for exactly one node + the current capacity
113		else
114		0;
115		if (mode == .free_all or current_capacity == 0) {
	111	const requested_capacity = switch (mode) {
	112	.retain_capacity => self.queryCapacity(),
	113	.retain_with_limit => \|limit\| std.math.min(limit, self.queryCapacity()),
	114	.free_all => 0,
	115	};
	116	if (requested_capacity == 0) {
116	117	// just reset when we don't have anything to reallocate
117	118	self.deinit();
118	119	self.state = State{};
119	120	return true;
120	121	}
121		const total_size = switch (mode) {
122		.retain_capacity => current_capacity,
123		.retain_with_limit => \|limit\| std.math.min(@sizeOf(BufNode) + limit, current_capacity),
124		.free_all => unreachable,
125		};
	122	const total_size = requested_capacity + @sizeOf(BufNode);
126	123	const align_bits = std.math.log2_int(usize, @alignOf(BufNode));
127	124	// Free all nodes except for the last one
128	125	var it = self.state.buffer_list.first;