Source/bmalloc/libpas/src/libpas/pas_segregated_shared_view.h

/*
 * Copyright (c) 2019-2020 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#ifndef PAS_SEGREGATED_SHARED_VIEW_H
#define PAS_SEGREGATED_SHARED_VIEW_H

#include "pas_segregated_page_config.h"
#include "pas_segregated_view.h"
#include "pas_shared_handle_or_page_boundary.h"
#include "pas_utils.h"

PAS_BEGIN_EXTERN_C;

struct pas_extended_segregated_shared_view;
struct pas_segregated_shared_view;
typedef struct pas_extended_segregated_shared_view pas_extended_segregated_shared_view;
typedef struct pas_segregated_shared_view pas_segregated_shared_view;

struct pas_segregated_shared_view {
    pas_shared_handle_or_page_boundary shared_handle_or_page_boundary;
    pas_lock commit_lock;
    pas_lock ownership_lock;
    unsigned index : 31;

    /* This has roughly the same meaning as in pas_segregated_exclusive_view. */
    bool is_owned : 1;
    
    unsigned bump_offset;
    unsigned is_in_use_for_allocation_count;
};

static inline pas_segregated_view pas_segregated_shared_view_as_view(pas_segregated_shared_view* view)
{
    return pas_segregated_view_create(view, pas_segregated_shared_view_kind);
}

static inline pas_segregated_view pas_segregated_shared_view_as_view_non_null(pas_segregated_shared_view* view)
{
    return pas_segregated_view_create_non_null(view, pas_segregated_shared_view_kind);
}

PAS_API pas_segregated_shared_view* pas_segregated_shared_view_create(size_t index);

typedef struct {
    unsigned old_bump; /* The start of the allocation. It's _not_ the old value of bump_offset,
                          since old_bump includes the alignment bump. */
    unsigned new_bump; /* What to set bump_offset to. */
    unsigned end_bump; /* The end of the allocation (end_bump <= new_bump). */
    unsigned num_objects; /* Number of objects in the range. */
} pas_shared_view_computed_bump_result;

static inline pas_shared_view_computed_bump_result
pas_shared_view_computed_bump_result_create_empty(void)
{
    pas_shared_view_computed_bump_result result;
    result.old_bump = 0;
    result.new_bump = 0;
    result.end_bump = 0;
    result.num_objects = 0;
    return result;
}

static PAS_ALWAYS_INLINE pas_shared_view_computed_bump_result
pas_segregated_shared_view_compute_initial_new_bump(
    pas_segregated_shared_view* view,
    unsigned size,
    unsigned alignment,
    pas_segregated_page_config page_config)
{
    pas_shared_view_computed_bump_result result;

    PAS_UNUSED_PARAM(page_config);

    /* NOTE: This math cannot overflow because size and alignment are bounded to page size, and
       page size is much smaller than 1 << 32. It's not up to this function to assert that bound
       since we expect this to be a hot path. Moreover it's the kind of hot path where it's hard
       to reduce the amount of work done anywhere else so we might as well not assert too much. */

    result.old_bump = view->bump_offset;
    result.old_bump = (unsigned)pas_round_up_to_power_of_2(result.old_bump, alignment);
    result.new_bump = result.old_bump;
    result.new_bump += size;
    result.end_bump = result.new_bump;
    result.num_objects = 1;

    return result;
}

static PAS_ALWAYS_INLINE bool
pas_segregated_shared_view_can_bump(
    pas_segregated_shared_view* view,
    unsigned size,
    unsigned alignment,
    pas_segregated_page_config page_config)
{
    pas_shared_view_computed_bump_result result;
    unsigned bump_limit;

    bump_limit = (unsigned)
        pas_segregated_page_config_object_payload_end_offset_from_boundary(page_config);
    result = pas_segregated_shared_view_compute_initial_new_bump(view, size, alignment, page_config);

    return result.new_bump <= bump_limit;
}

static PAS_ALWAYS_INLINE pas_shared_view_computed_bump_result
pas_segregated_shared_view_compute_new_bump(
    pas_segregated_shared_view* view,
    unsigned size,
    unsigned alignment,
    pas_segregated_page_config page_config)
{
    pas_shared_view_computed_bump_result result;
    unsigned total_shift;
    unsigned bump_limit;

    total_shift = page_config.base.min_align_shift + page_config.sharing_shift;
    bump_limit = (unsigned)
        pas_segregated_page_config_object_payload_end_offset_from_boundary(page_config);
    result = pas_segregated_shared_view_compute_initial_new_bump(view, size, alignment, page_config);

    if (result.new_bump > bump_limit)
        return pas_shared_view_computed_bump_result_create_empty();
    
    while ((result.new_bump >> total_shift) == (result.old_bump >> total_shift)) {
        result.new_bump += size;

        if (result.new_bump > bump_limit) {
            result.new_bump = bump_limit;
            break;
        }

        result.end_bump = result.new_bump;
        result.num_objects++;
    }

    return result;
}

static PAS_ALWAYS_INLINE pas_shared_view_computed_bump_result
pas_segregated_shared_view_bump(
    pas_segregated_shared_view* view,
    unsigned size,
    unsigned alignment,
    pas_segregated_page_config page_config)
{
    pas_shared_view_computed_bump_result result;
    
    result = pas_segregated_shared_view_compute_new_bump(
        view, size, alignment, page_config);
    
    if (result.num_objects)
        view->bump_offset = result.new_bump;
    
    return result;
}

PAS_API pas_heap_summary
pas_segregated_shared_view_compute_summary(pas_segregated_shared_view* view,
                                           pas_segregated_page_config* page_config);

PAS_API bool pas_segregated_shared_view_is_empty(pas_segregated_shared_view* view);

PAS_END_EXTERN_C;

#endif /* PAS_SEGREGATED_SHARED_VIEW_H */