/**
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* \file
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* Object allocation routines + managed allocators
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*
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* Author:
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* Paolo Molaro (lupus@ximian.com)
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* Rodrigo Kumpera (kumpera@gmail.com)
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*
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* Copyright 2005-2011 Novell, Inc (http://www.novell.com)
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* Copyright 2011 Xamarin Inc (http://www.xamarin.com)
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* Copyright 2011 Xamarin, Inc.
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* Copyright (C) 2012 Xamarin Inc
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*
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* Licensed under the MIT license. See LICENSE file in the project root for full license information.
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*/
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/*
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* ######################################################################
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* ######## Object allocation
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* ######################################################################
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* This section of code deals with allocating memory for objects.
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* There are several ways:
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* *) allocate large objects
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* *) allocate normal objects
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* *) fast lock-free allocation
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* *) allocation of pinned objects
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*/
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#include "config.h"
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#ifdef HAVE_SGEN_GC
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#include <string.h>
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#include "mono/sgen/sgen-gc.h"
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#include "mono/sgen/sgen-protocol.h"
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#include "mono/sgen/sgen-memory-governor.h"
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#include "mono/sgen/sgen-client.h"
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#include "mono/utils/mono-memory-model.h"
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#define ALIGN_UP SGEN_ALIGN_UP
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#define ALLOC_ALIGN SGEN_ALLOC_ALIGN
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#define MAX_SMALL_OBJ_SIZE SGEN_MAX_SMALL_OBJ_SIZE
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#ifdef HEAVY_STATISTICS
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static guint64 stat_objects_alloced = 0;
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static guint64 stat_bytes_alloced = 0;
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static guint64 stat_bytes_alloced_los = 0;
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#endif
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/*
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* Allocation is done from a Thread Local Allocation Buffer (TLAB). TLABs are allocated
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* from nursery fragments.
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* tlab_next is the pointer to the space inside the TLAB where the next object will
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* be allocated.
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* tlab_temp_end is the pointer to the end of the temporary space reserved for
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* the allocation: it allows us to set the scan starts at reasonable intervals.
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* tlab_real_end points to the end of the TLAB.
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*/
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#define TLAB_START (__thread_info__->tlab_start)
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#define TLAB_NEXT (__thread_info__->tlab_next)
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#define TLAB_TEMP_END (__thread_info__->tlab_temp_end)
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#define TLAB_REAL_END (__thread_info__->tlab_real_end)
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static GCObject*
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alloc_degraded (GCVTable vtable, size_t size, gboolean for_mature)
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{
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GCObject *p;
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if (!for_mature) {
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sgen_client_degraded_allocation ();
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SGEN_ATOMIC_ADD_P (degraded_mode, size);
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sgen_ensure_free_space (size, GENERATION_OLD);
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} else {
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if (sgen_need_major_collection (size))
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sgen_perform_collection (size, GENERATION_OLD, "mature allocation failure", !for_mature, TRUE);
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}
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p = major_collector.alloc_degraded (vtable, size);
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if (!for_mature)
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binary_protocol_alloc_degraded (p, vtable, size, sgen_client_get_provenance ());
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return p;
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}
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static void
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zero_tlab_if_necessary (void *p, size_t size)
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{
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if (nursery_clear_policy == CLEAR_AT_TLAB_CREATION || nursery_clear_policy == CLEAR_AT_TLAB_CREATION_DEBUG) {
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memset (p, 0, size);
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} else {
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/*
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* This function is called for all allocations in
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* TLABs. TLABs originate from fragments, which are
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* initialized to be faux arrays. The remainder of
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* the fragments are zeroed out at initialization for
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* CLEAR_AT_GC, so here we just need to make sure that
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* the array header is zeroed. Since we don't know
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* whether we're called for the start of a fragment or
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* for somewhere in between, we zero in any case, just
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* to make sure.
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*/
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sgen_client_zero_array_fill_header (p, size);
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}
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}
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/*
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* Provide a variant that takes just the vtable for small fixed-size objects.
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* The aligned size is already computed and stored in vt->gc_descr.
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* Note: every SGEN_SCAN_START_SIZE or so we are given the chance to do some special
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* processing. We can keep track of where objects start, for example,
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* so when we scan the thread stacks for pinned objects, we can start
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* a search for the pinned object in SGEN_SCAN_START_SIZE chunks.
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*/
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GCObject*
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sgen_alloc_obj_nolock (GCVTable vtable, size_t size)
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{
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/* FIXME: handle OOM */
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void **p;
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char *new_next;
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size_t real_size = size;
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TLAB_ACCESS_INIT;
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CANARIFY_SIZE(size);
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HEAVY_STAT (++stat_objects_alloced);
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if (real_size <= SGEN_MAX_SMALL_OBJ_SIZE)
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HEAVY_STAT (stat_bytes_alloced += size);
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else
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HEAVY_STAT (stat_bytes_alloced_los += size);
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size = ALIGN_UP (size);
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SGEN_ASSERT (6, sgen_vtable_get_descriptor (vtable), "VTable without descriptor");
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if (G_UNLIKELY (has_per_allocation_action)) {
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static int alloc_count;
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int current_alloc = mono_atomic_inc_i32 (&alloc_count);
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if (collect_before_allocs) {
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if (((current_alloc % collect_before_allocs) == 0) && nursery_section) {
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sgen_perform_collection (0, GENERATION_NURSERY, "collect-before-alloc-triggered", TRUE, TRUE);
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if (!degraded_mode && sgen_can_alloc_size (size) && real_size <= SGEN_MAX_SMALL_OBJ_SIZE) {
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// FIXME:
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g_assert_not_reached ();
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}
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}
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} else if (verify_before_allocs) {
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if ((current_alloc % verify_before_allocs) == 0)
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sgen_check_whole_heap_stw ();
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}
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}
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/*
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* We must already have the lock here instead of after the
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* fast path because we might be interrupted in the fast path
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* (after confirming that new_next < TLAB_TEMP_END) by the GC,
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* and we'll end up allocating an object in a fragment which
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* no longer belongs to us.
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*
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* The managed allocator does not do this, but it's treated
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* specially by the world-stopping code.
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*/
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if (real_size > SGEN_MAX_SMALL_OBJ_SIZE) {
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p = (void **)sgen_los_alloc_large_inner (vtable, ALIGN_UP (real_size));
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} else {
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/* tlab_next and tlab_temp_end are TLS vars so accessing them might be expensive */
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p = (void**)TLAB_NEXT;
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/* FIXME: handle overflow */
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new_next = (char*)p + size;
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TLAB_NEXT = new_next;
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if (G_LIKELY (new_next < TLAB_TEMP_END)) {
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/* Fast path */
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CANARIFY_ALLOC(p,real_size);
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SGEN_LOG (6, "Allocated object %p, vtable: %p (%s), size: %zd", p, vtable, sgen_client_vtable_get_name (vtable), size);
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binary_protocol_alloc (p , vtable, size, sgen_client_get_provenance ());
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g_assert (*p == NULL);
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mono_atomic_store_seq (p, vtable);
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return (GCObject*)p;
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}
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/* Slow path */
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/* there are two cases: the object is too big or we run out of space in the TLAB */
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/* we also reach here when the thread does its first allocation after a minor
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* collection, since the tlab_ variables are initialized to NULL.
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* there can be another case (from ORP), if we cooperate with the runtime a bit:
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* objects that need finalizers can have the high bit set in their size
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* so the above check fails and we can readily add the object to the queue.
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* This avoids taking again the GC lock when registering, but this is moot when
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* doing thread-local allocation, so it may not be a good idea.
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*/
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if (TLAB_NEXT >= TLAB_REAL_END) {
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int available_in_tlab;
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/*
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* Run out of space in the TLAB. When this happens, some amount of space
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* remains in the TLAB, but not enough to satisfy the current allocation
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* request. Currently, we retire the TLAB in all cases, later we could
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* keep it if the remaining space is above a treshold, and satisfy the
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* allocation directly from the nursery.
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*/
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TLAB_NEXT -= size;
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/* when running in degraded mode, we continue allocing that way
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* for a while, to decrease the number of useless nursery collections.
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*/
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if (degraded_mode && degraded_mode < sgen_nursery_size)
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return alloc_degraded (vtable, size, FALSE);
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available_in_tlab = (int)(TLAB_REAL_END - TLAB_NEXT);//We'll never have tlabs > 2Gb
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if (size > tlab_size || available_in_tlab > SGEN_MAX_NURSERY_WASTE) {
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/* Allocate directly from the nursery */
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p = (void **)sgen_nursery_alloc (size);
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if (!p) {
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/*
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* We couldn't allocate from the nursery, so we try
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* collecting. Even after the collection, we might
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* still not have enough memory to allocate the
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* object. The reason will most likely be that we've
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* run out of memory, but there is the theoretical
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* possibility that other threads might have consumed
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* the freed up memory ahead of us.
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*
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* What we do in this case is allocate degraded, i.e.,
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* from the major heap.
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*
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* Ideally we'd like to detect the case of other
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* threads allocating ahead of us and loop (if we
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* always loop we will loop endlessly in the case of
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* OOM).
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*/
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sgen_ensure_free_space (real_size, GENERATION_NURSERY);
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if (!degraded_mode)
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p = (void **)sgen_nursery_alloc (size);
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}
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if (!p)
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return alloc_degraded (vtable, size, TRUE);
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zero_tlab_if_necessary (p, size);
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} else {
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size_t alloc_size = 0;
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if (TLAB_START)
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SGEN_LOG (3, "Retire TLAB: %p-%p [%ld]", TLAB_START, TLAB_REAL_END, (long)(TLAB_REAL_END - TLAB_NEXT - size));
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sgen_nursery_retire_region (p, available_in_tlab);
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p = (void **)sgen_nursery_alloc_range (tlab_size, size, &alloc_size);
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if (!p) {
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/* See comment above in similar case. */
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sgen_ensure_free_space (tlab_size, GENERATION_NURSERY);
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if (!degraded_mode)
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p = (void **)sgen_nursery_alloc_range (tlab_size, size, &alloc_size);
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}
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if (!p)
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return alloc_degraded (vtable, size, TRUE);
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/* Allocate a new TLAB from the current nursery fragment */
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TLAB_START = (char*)p;
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TLAB_NEXT = TLAB_START;
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TLAB_REAL_END = TLAB_START + alloc_size;
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TLAB_TEMP_END = TLAB_START + MIN (SGEN_SCAN_START_SIZE, alloc_size);
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zero_tlab_if_necessary (TLAB_START, alloc_size);
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/* Allocate from the TLAB */
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p = (void **)TLAB_NEXT;
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TLAB_NEXT += size;
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sgen_set_nursery_scan_start ((char*)p);
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}
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} else {
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/* Reached tlab_temp_end */
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/* record the scan start so we can find pinned objects more easily */
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sgen_set_nursery_scan_start ((char*)p);
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/* we just bump tlab_temp_end as well */
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TLAB_TEMP_END = MIN (TLAB_REAL_END, TLAB_NEXT + SGEN_SCAN_START_SIZE);
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SGEN_LOG (5, "Expanding local alloc: %p-%p", TLAB_NEXT, TLAB_TEMP_END);
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}
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CANARIFY_ALLOC(p,real_size);
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}
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if (G_LIKELY (p)) {
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SGEN_LOG (6, "Allocated object %p, vtable: %p (%s), size: %zd", p, vtable, sgen_client_vtable_get_name (vtable), size);
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binary_protocol_alloc (p, vtable, size, sgen_client_get_provenance ());
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mono_atomic_store_seq (p, vtable);
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}
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return (GCObject*)p;
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}
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GCObject*
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sgen_try_alloc_obj_nolock (GCVTable vtable, size_t size)
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{
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void **p;
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char *new_next;
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size_t real_size = size;
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TLAB_ACCESS_INIT;
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CANARIFY_SIZE(size);
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size = ALIGN_UP (size);
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SGEN_ASSERT (9, real_size >= SGEN_CLIENT_MINIMUM_OBJECT_SIZE, "Object too small");
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SGEN_ASSERT (6, sgen_vtable_get_descriptor (vtable), "VTable without descriptor");
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if (real_size > SGEN_MAX_SMALL_OBJ_SIZE)
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return NULL;
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if (G_UNLIKELY (size > tlab_size)) {
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/* Allocate directly from the nursery */
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p = (void **)sgen_nursery_alloc (size);
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if (!p)
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return NULL;
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sgen_set_nursery_scan_start ((char*)p);
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/*FIXME we should use weak memory ops here. Should help specially on x86. */
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zero_tlab_if_necessary (p, size);
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} else {
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int available_in_tlab;
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char *real_end;
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/* tlab_next and tlab_temp_end are TLS vars so accessing them might be expensive */
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p = (void**)TLAB_NEXT;
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/* FIXME: handle overflow */
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new_next = (char*)p + size;
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real_end = TLAB_REAL_END;
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available_in_tlab = (int)(real_end - (char*)p);//We'll never have tlabs > 2Gb
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if (G_LIKELY (new_next < real_end)) {
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TLAB_NEXT = new_next;
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/* Second case, we overflowed temp end */
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if (G_UNLIKELY (new_next >= TLAB_TEMP_END)) {
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sgen_set_nursery_scan_start (new_next);
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/* we just bump tlab_temp_end as well */
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TLAB_TEMP_END = MIN (TLAB_REAL_END, TLAB_NEXT + SGEN_SCAN_START_SIZE);
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SGEN_LOG (5, "Expanding local alloc: %p-%p", TLAB_NEXT, TLAB_TEMP_END);
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}
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} else if (available_in_tlab > SGEN_MAX_NURSERY_WASTE) {
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/* Allocate directly from the nursery */
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p = (void **)sgen_nursery_alloc (size);
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if (!p)
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return NULL;
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zero_tlab_if_necessary (p, size);
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} else {
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size_t alloc_size = 0;
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sgen_nursery_retire_region (p, available_in_tlab);
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new_next = (char *)sgen_nursery_alloc_range (tlab_size, size, &alloc_size);
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p = (void**)new_next;
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if (!p)
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return NULL;
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TLAB_START = (char*)new_next;
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TLAB_NEXT = new_next + size;
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TLAB_REAL_END = new_next + alloc_size;
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TLAB_TEMP_END = new_next + MIN (SGEN_SCAN_START_SIZE, alloc_size);
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sgen_set_nursery_scan_start ((char*)p);
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zero_tlab_if_necessary (new_next, alloc_size);
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}
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}
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HEAVY_STAT (++stat_objects_alloced);
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HEAVY_STAT (stat_bytes_alloced += size);
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CANARIFY_ALLOC(p,real_size);
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SGEN_LOG (6, "Allocated object %p, vtable: %p (%s), size: %zd", p, vtable, sgen_client_vtable_get_name (vtable), size);
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binary_protocol_alloc (p, vtable, size, sgen_client_get_provenance ());
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g_assert (*p == NULL); /* FIXME disable this in non debug builds */
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mono_atomic_store_seq (p, vtable);
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return (GCObject*)p;
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}
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GCObject*
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sgen_alloc_obj (GCVTable vtable, size_t size)
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{
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GCObject *res;
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TLAB_ACCESS_INIT;
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if (!SGEN_CAN_ALIGN_UP (size))
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return NULL;
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if (G_UNLIKELY (has_per_allocation_action)) {
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static int alloc_count;
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int current_alloc = mono_atomic_inc_i32 (&alloc_count);
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if (verify_before_allocs) {
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if ((current_alloc % verify_before_allocs) == 0) {
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LOCK_GC;
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sgen_check_whole_heap_stw ();
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UNLOCK_GC;
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}
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}
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if (collect_before_allocs) {
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if (((current_alloc % collect_before_allocs) == 0) && nursery_section) {
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LOCK_GC;
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sgen_perform_collection (0, GENERATION_NURSERY, "collect-before-alloc-triggered", TRUE, TRUE);
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UNLOCK_GC;
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}
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}
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}
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ENTER_CRITICAL_REGION;
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res = sgen_try_alloc_obj_nolock (vtable, size);
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if (res) {
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EXIT_CRITICAL_REGION;
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return res;
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}
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EXIT_CRITICAL_REGION;
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LOCK_GC;
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res = sgen_alloc_obj_nolock (vtable, size);
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UNLOCK_GC;
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return res;
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}
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/*
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* To be used for interned strings and possibly MonoThread, reflection handles.
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* We may want to explicitly free these objects.
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*/
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GCObject*
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sgen_alloc_obj_pinned (GCVTable vtable, size_t size)
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{
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GCObject *p;
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if (!SGEN_CAN_ALIGN_UP (size))
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return NULL;
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size = ALIGN_UP (size);
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LOCK_GC;
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if (size > SGEN_MAX_SMALL_OBJ_SIZE) {
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/* large objects are always pinned anyway */
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p = (GCObject *)sgen_los_alloc_large_inner (vtable, size);
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} else {
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SGEN_ASSERT (9, sgen_client_vtable_is_inited (vtable), "class %s:%s is not initialized", sgen_client_vtable_get_namespace (vtable), sgen_client_vtable_get_name (vtable));
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p = major_collector.alloc_small_pinned_obj (vtable, size, SGEN_VTABLE_HAS_REFERENCES (vtable));
|
}
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if (G_LIKELY (p)) {
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SGEN_LOG (6, "Allocated pinned object %p, vtable: %p (%s), size: %zd", p, vtable, sgen_client_vtable_get_name (vtable), size);
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binary_protocol_alloc_pinned (p, vtable, size, sgen_client_get_provenance ());
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}
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UNLOCK_GC;
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return p;
|
}
|
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GCObject*
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sgen_alloc_obj_mature (GCVTable vtable, size_t size)
|
{
|
GCObject *res;
|
|
if (!SGEN_CAN_ALIGN_UP (size))
|
return NULL;
|
size = ALIGN_UP (size);
|
|
LOCK_GC;
|
res = alloc_degraded (vtable, size, TRUE);
|
UNLOCK_GC;
|
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return res;
|
}
|
|
/*
|
* Clear the thread local TLAB variables for all threads.
|
*/
|
void
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sgen_clear_tlabs (void)
|
{
|
FOREACH_THREAD (info) {
|
/* A new TLAB will be allocated when the thread does its first allocation */
|
info->tlab_start = NULL;
|
info->tlab_next = NULL;
|
info->tlab_temp_end = NULL;
|
info->tlab_real_end = NULL;
|
} FOREACH_THREAD_END
|
}
|
|
void
|
sgen_init_allocator (void)
|
{
|
#ifdef HEAVY_STATISTICS
|
mono_counters_register ("# objects allocated", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_objects_alloced);
|
mono_counters_register ("bytes allocated", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_bytes_alloced);
|
mono_counters_register ("bytes allocated in LOS", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_bytes_alloced_los);
|
#endif
|
}
|
|
#endif /*HAVE_SGEN_GC*/
|
