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resize

SafeAllocator.resize

fn resize(ctx: *anyopaque, memory: []u8, alignment: Alignment, new_len: usize, ra: usize) bool

File

lib/std/heap/SafeAllocator.zig:1178

Code

fn resize(ctx: *anyopaque, memory: []u8, alignment: Alignment, new_len: usize, ra: usize) bool {
    assert(new_len != 0);

    const s: *SafeAllocator = @ptrCast(@alignCast(ctx));
    const f: *AllocFooter = .of(memory);
    f.startModify(.resized, s, .{ .memory = memory, .alignment = alignment });

    // Check that the allocation is not moving between a bucket and large allocation. This is
    // done after the above so that it is still checked that valid memory is passed and there
    // is no double modify.
    const from_large_alloc = s.isLarge(memory.len, alignment);
    const to_large_alloc = s.isLargeOrOom(new_len, alignment) catch {
        f.modify.setNone();
        return false;
    };
    if (from_large_alloc != to_large_alloc) {
        @branchHint(.unlikely);
        f.modify.setNone();
        return false;
    }

    if (from_large_alloc) {
        @branchHint(.unlikely);

        const entry = f.extended().container.large_entry;
        const new_alloc_len = AllocFooter.allocLenLarge(s, new_len);
        if (!s.backing.rawResize(
            memory.ptr[0..AllocFooter.allocLenLarge(s, memory.len)],
            AllocFooter.allocAlign(alignment),
            new_alloc_len,
            ra,
        )) {
            f.modify.setNone();
            return false;
        }

        const new_footer = AllocFooter.populate(
            @alignCast(memory.ptr[0..new_alloc_len]),
            new_len,
            alignment,
            ra,
            true,
            false,
            .{ .large_entry = entry },
            s,
        );
        assert(entry.kind == .large_alloc);
        entry.* = .fromLargeAlloc(new_footer);
        return true;
    }

    if (new_len < memory.len) {
        // Resize shrinks are disallowed in all cases since the linked list would be broken. Even
        // if this footer is the final one, the fill value would need decreased which would allow
        // memory to be reused.
        f.modify.setNone();
        return false;
    }

    if (s.growingResizeBucket(f, memory, alignment, new_len, ra)) {
        @branchHint(.likely);
        return true;
    } else {
        f.modify.setNone();
        return false;
    }
}