Mozilla/mozilla/js2/src/mem.cpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
*
* The contents of this file are subject to the Netscape Public
* License Version 1.1 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of
* the License at http://www.mozilla.org/NPL/
*
* Software distributed under the License is distributed on an "AS
* IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
* implied. See the License for the specific language governing
* rights and limitations under the License.
*
* The Original Code is the JavaScript 2 Prototype.
*
* The Initial Developer of the Original Code is Netscape
* Communications Corporation.  Portions created by Netscape are
* Copyright (C) 1998 Netscape Communications Corporation. All
* Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the
* terms of the GNU Public License (the "GPL"), in which case the
* provisions of the GPL are applicable instead of those above.
* If you wish to allow use of your version of this file only
* under the terms of the GPL and not to allow others to use your
* version of this file under the NPL, indicate your decision by
* deleting the provisions above and replace them with the notice
* and other provisions required by the GPL.  If you do not delete
* the provisions above, a recipient may use your version of this
* file under either the NPL or the GPL.
*/

#include <memory>

#include "mem.h"

namespace JS = JavaScript;


//
// Zones
//

// #define DEBUG_ZONE to allocate each object in its own malloc block.
// This allows tools such as Purify to do bounds checking on all blocks.


// Construct a Zone that allocates memory in chunks of the given size.
JS::Zone::Zone(size_t blockSize):
        headers(0), freeBegin(0), freeEnd(0), blockSize(blockSize)
{
    ASSERT(blockSize && !(blockSize & basicAlignment-1));
}


// Deallocate the Zone's blocks.
void JS::Zone::clear()
{
    Header *h = headers;
    while (h) {
        Header *next = h->next;
        STD::free(h);
        h = next;
    }
    headers = 0;
}


// Allocate a fully aligned block of the given size.
// Throw bad_alloc if out of memory, without corrupting any of the Zone data
// structures.
void *JS::Zone::newBlock(size_t size)
{
    Header *h = static_cast<Header *>(STD::malloc(sizeof(Header) + size));
    h->next = headers;
    headers = h;
    return h+1;
}


// Allocate a naturally-aligned object of the given size (in bytes).  Throw
// bad_alloc if out of memory, without corrupting any of the Zone data structures.
void *JS::Zone::allocate(size_t size)
{
    ASSERT(size);   // Can't allocate zero-size blocks.
#ifdef DEBUG_ZONE
    return newBlock(size);
#else
    // Round up to natural alignment if necessary
    size = size + (basicAlignment-1) & -basicAlignment;
    char *p = freeBegin;
    size_t freeBytes = toSize_t(freeEnd - p);

    if (size > freeBytes) {
        // If freeBytes is at least a quarter of blockSize, allocate a separate block.
        if (freeBytes<<2 >= blockSize || size >= blockSize)
            return newBlock(size);

        p = static_cast<char *>(newBlock(blockSize));
        freeEnd = p + blockSize;
    }
    freeBegin = p + size;
    return p;
#endif
}


// Same as allocate but does not align size up to basicAlignment.  Thus, the
// next object allocated in the zone will immediately follow this one if it
// falls in the same zone block.
// Use this when all objects in the zone have the same size.
void *JS::Zone::allocateUnaligned(size_t size)
{
    ASSERT(size);   // Can't allocate zero-size blocks.
#ifdef DEBUG_ZONE
    return newBlock(size);
#else
    char *p = freeBegin;
    size_t freeBytes = toSize_t(freeEnd - p);

    if (size > freeBytes) {
        // If freeBytes is at least a quarter of blockSize, allocate a separate block.
        if (freeBytes<<2 >= blockSize || size >= blockSize)
            return newBlock(size);

        p = static_cast<char *>(newBlock(blockSize));
        freeEnd = p + blockSize;
    }
    freeBegin = p + size;
    return p;
#endif
}


//
// Arenas
//

struct JS::Arena::DestructorEntry: JS::ArenaObject {
    DestructorEntry *next;              // Next destructor registration in linked list
    void (*destructor)(void *);         // Destructor function
    void *object;                       // Object on which to call the destructor

    DestructorEntry (void (*destructor)(void *), void *object) :
            destructor(destructor), object(object) {}
};


// Call the Arena's registered destructors.
void JS::Arena::runDestructors()
{
    DestructorEntry *e = destructorEntries;
    while (e) {
        e->destructor(e->object);
        e = e->next;
    }
    destructorEntries = 0;
}


// Ensure that object's destructor is called at the time the arena is
// deallocated or cleared. The destructors will be called in reverse order of
// being registered. registerDestructor might itself runs out of memory, in
// which case it immediately calls object's destructor before throwing
// bad_alloc.
void JS::Arena::newDestructorEntry(void (*destructor)(void *), void *object)
{
    try {
        DestructorEntry *e = new(*this) DestructorEntry(destructor, object);
        e->next = destructorEntries;
        destructorEntries = e;
    } catch (...) {
        destructor(object);
        throw;
    }
}