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std.mem.Allocator: introduce remap function to the interface

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This one changes the size of an allocation, allowing it to be relocated.
However, the implementation will still return `null` if it would be
equivalent to

new = alloc
memcpy(new, old)
free(old)

Mainly this prepares for taking advantage of `mremap` which I thought
would be a bigger deal but apparently is only available on Linux. Still,
we should use it on Linux.
This commit is contained in:
Andrew Kelley
2025-02-03 19:55:09 -08:00
parent dd2fa4f75d
commit 7eeef5fb2b
7 changed files with 404 additions and 232 deletions
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37
lib/std/array_list.zig
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@@ -105,21 +105,19 @@ pub fn ArrayListAligned(comptime T: type, comptime alignment: ?u29) type {
return result;
}
/// The caller owns the returned memory. Empties this ArrayList,
/// Its capacity is cleared, making deinit() safe but unnecessary to call.
/// The caller owns the returned memory. Empties this ArrayList.
/// Its capacity is cleared, making `deinit` safe but unnecessary to call.
pub fn toOwnedSlice(self: *Self) Allocator.Error!Slice {
const allocator = self.allocator;
const old_memory = self.allocatedSlice();
if (allocator.resize(old_memory, self.items.len)) {
const result = self.items;
if (allocator.remap(old_memory, self.items.len)) |new_items| {
self.* = init(allocator);
return result;
return new_items;
}
const new_memory = try allocator.alignedAlloc(T, alignment, self.items.len);
@memcpy(new_memory, self.items);
@memset(self.items, undefined);
self.clearAndFree();
return new_memory;
}
@@ -185,8 +183,9 @@ pub fn ArrayListAligned(comptime T: type, comptime alignment: ?u29) type {
// extra capacity.
const new_capacity = growCapacity(self.capacity, new_len);
const old_memory = self.allocatedSlice();
if (self.allocator.resize(old_memory, new_capacity)) {
self.capacity = new_capacity;
if (self.allocator.remap(old_memory, new_capacity)) |new_memory| {
self.items.ptr = new_memory.ptr;
self.capacity = new_memory.len;
return addManyAtAssumeCapacity(self, index, count);
}
@@ -468,8 +467,9 @@ pub fn ArrayListAligned(comptime T: type, comptime alignment: ?u29) type {
// the allocator implementation would pointlessly copy our
// extra capacity.
const old_memory = self.allocatedSlice();
if (self.allocator.resize(old_memory, new_capacity)) {
self.capacity = new_capacity;
if (self.allocator.remap(old_memory, new_capacity)) |new_memory| {
self.items.ptr = new_memory.ptr;
self.capacity = new_memory.len;
} else {
const new_memory = try self.allocator.alignedAlloc(T, alignment, new_capacity);
@memcpy(new_memory[0..self.items.len], self.items);
@@ -707,15 +707,13 @@ pub fn ArrayListAlignedUnmanaged(comptime T: type, comptime alignment: ?u29) typ
/// Its capacity is cleared, making deinit() safe but unnecessary to call.
pub fn toOwnedSlice(self: *Self, allocator: Allocator) Allocator.Error!Slice {
const old_memory = self.allocatedSlice();
if (allocator.resize(old_memory, self.items.len)) {
const result = self.items;
if (allocator.remap(old_memory, self.items.len)) |new_items| {
self.* = .empty;
return result;
return new_items;
}
const new_memory = try allocator.alignedAlloc(T, alignment, self.items.len);
@memcpy(new_memory, self.items);
@memset(self.items, undefined);
self.clearAndFree(allocator);
return new_memory;
}
@@ -1031,9 +1029,9 @@ pub fn ArrayListAlignedUnmanaged(comptime T: type, comptime alignment: ?u29) typ
}
const old_memory = self.allocatedSlice();
if (allocator.resize(old_memory, new_len)) {
self.capacity = new_len;
self.items.len = new_len;
if (allocator.remap(old_memory, new_len)) |new_items| {
self.capacity = new_items.len;
self.items = new_items;
return;
}
@@ -1099,8 +1097,9 @@ pub fn ArrayListAlignedUnmanaged(comptime T: type, comptime alignment: ?u29) typ
// the allocator implementation would pointlessly copy our
// extra capacity.
const old_memory = self.allocatedSlice();
if (allocator.resize(old_memory, new_capacity)) {
self.capacity = new_capacity;
if (allocator.remap(old_memory, new_capacity)) |new_memory| {
self.items.ptr = new_memory.ptr;
self.capacity = new_memory.len;
} else {
const new_memory = try allocator.alignedAlloc(T, alignment, new_capacity);
@memcpy(new_memory[0..self.items.len], self.items);