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#
#
# Nim's Runtime Library
# (c) Copyright 2019 Andreas Rumpf
#
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
#
#[
In this new runtime we simplify the object layouts a bit: The runtime type
information is only accessed for the objects that have it and it's always
at offset 0 then. The ``ref`` object header is independent from the
runtime type and only contains a reference count.
Object subtyping is checked via the generated 'name'. This should have
comparable overhead to the old pointer chasing approach but has the benefit
that it works across DLL boundaries.
The generated name is a concatenation of the object names in the hierarchy
so that a subtype check becomes a substring check. For example::
type
ObjectA = object of RootObj
ObjectB = object of ObjectA
ObjectA's ``name`` is "|ObjectA|RootObj|".
ObjectB's ``name`` is "|ObjectB|ObjectA|RootObj|".
Now to check for ``x of ObjectB`` we need to check
for ``x.typ.name.hasSubstring("|ObjectB|")``. In the actual implementation,
however, we could also use a
hash of ``package & "." & module & "." & name`` to save space.
]#
when defined(gcOrc):
const
rcIncrement = 0b10000 # so that lowest 4 bits are not touched
rcMask = 0b1111
rcShift = 4 # shift by rcShift to get the reference counter
else:
const
rcIncrement = 0b1000 # so that lowest 3 bits are not touched
rcMask = 0b111
rcShift = 3 # shift by rcShift to get the reference counter
type
RefHeader = object
rc: int # the object header is now a single RC field.
# we could remove it in non-debug builds for the 'owned ref'
# design but this seems unwise.
when defined(gcOrc):
rootIdx: int # thanks to this we can delete potential cycle roots
# in O(1) without doubly linked lists
when defined(nimArcDebug) or defined(nimArcIds):
refId: int
Cell = ptr RefHeader
template head(p: pointer): Cell =
cast[Cell](cast[int](p) -% sizeof(RefHeader))
const
traceCollector = defined(traceArc)
when defined(nimArcDebug):
include cellsets
const traceId = 20 # 1037
var gRefId: int
var freedCells: CellSet
elif defined(nimArcIds):
var gRefId: int
proc nimNewObj(size, alignment: int): pointer {.compilerRtl.} =
let hdrSize = align(sizeof(RefHeader), alignment)
let s = size + hdrSize
when defined(nimscript):
discard
else:
result = alignedAlloc0(s, alignment) +! hdrSize
when defined(nimArcDebug) or defined(nimArcIds):
head(result).refId = gRefId
atomicInc gRefId
if head(result).refId == traceId:
writeStackTrace()
cfprintf(cstderr, "[nimNewObj] %p %ld\n", result, head(result).rc shr rcShift)
when traceCollector:
cprintf("[Allocated] %p result: %p\n", result -! sizeof(RefHeader), result)
proc nimNewObjUninit(size, alignment: int): pointer {.compilerRtl.} =
# Same as 'newNewObj' but do not initialize the memory to zero.
# The codegen proved for us that this is not necessary.
let hdrSize = align(sizeof(RefHeader), alignment)
let s = size + hdrSize
when defined(nimscript):
discard
else:
result = cast[ptr RefHeader](alignedAlloc0(s, alignment) +! hdrSize)
head(result).rc = 0
when defined(gcOrc):
head(result).rootIdx = 0
when defined(nimArcDebug):
head(result).refId = gRefId
atomicInc gRefId
if head(result).refId == traceId:
writeStackTrace()
cfprintf(cstderr, "[nimNewObjUninit] %p %ld\n", result, head(result).rc shr rcShift)
when traceCollector:
cprintf("[Allocated] %p result: %p\n", result -! sizeof(RefHeader), result)
proc nimDecWeakRef(p: pointer) {.compilerRtl, inl.} =
dec head(p).rc, rcIncrement
proc nimIncRef(p: pointer) {.compilerRtl, inl.} =
when defined(nimArcDebug):
if head(p).refId == traceId:
writeStackTrace()
cfprintf(cstderr, "[IncRef] %p %ld\n", p, head(p).rc shr rcShift)
inc head(p).rc, rcIncrement
when traceCollector:
cprintf("[INCREF] %p\n", head(p))
proc unsureAsgnRef(dest: ptr pointer, src: pointer) {.inline.} =
# This is only used by the old RTTI mechanism and we know
# that 'dest[]' is nil and needs no destruction. Which is really handy
# as we cannot destroy the object reliably if it's an object of unknown
# compile-time type.
dest[] = src
if src != nil: nimIncRef src
when not defined(nimscript) and defined(nimArcDebug):
proc deallocatedRefId*(p: pointer): int =
## Returns the ref's ID if the ref was already deallocated. This
## is a memory corruption check. Returns 0 if there is no error.
let c = head(p)
if freedCells.data != nil and freedCells.contains(c):
result = c.refId
else:
result = 0
proc nimRawDispose(p: pointer, alignment: int) {.compilerRtl.} =
when not defined(nimscript):
when traceCollector:
cprintf("[Freed] %p\n", p -! sizeof(RefHeader))
when defined(nimOwnedEnabled):
if head(p).rc >= rcIncrement:
cstderr.rawWrite "[FATAL] dangling references exist\n"
quit 1
when defined(nimArcDebug):
# we do NOT really free the memory here in order to reliably detect use-after-frees
if freedCells.data == nil: init(freedCells)
freedCells.incl head(p)
else:
let hdrSize = align(sizeof(RefHeader), alignment)
alignedDealloc(p -! hdrSize, alignment)
template dispose*[T](x: owned(ref T)) = nimRawDispose(cast[pointer](x), T.alignOf)
#proc dispose*(x: pointer) = nimRawDispose(x)
proc nimDestroyAndDispose(p: pointer) {.compilerRtl, raises: [].} =
let rti = cast[ptr PNimTypeV2](p)
if rti.destructor != nil:
cast[DestructorProc](rti.destructor)(p)
when false:
cstderr.rawWrite cast[ptr PNimTypeV2](p)[].name
cstderr.rawWrite "\n"
if d == nil:
cstderr.rawWrite "bah, nil\n"
else:
cstderr.rawWrite "has destructor!\n"
nimRawDispose(p, rti.align)
when defined(gcOrc):
when defined(nimThinout):
include cyclebreaker
else:
include orc
#include cyclecollector
proc nimDecRefIsLast(p: pointer): bool {.compilerRtl, inl.} =
if p != nil:
var cell = head(p)
when defined(nimArcDebug):
if cell.refId == traceId:
writeStackTrace()
cfprintf(cstderr, "[DecRef] %p %ld\n", p, cell.rc shr rcShift)
if (cell.rc and not rcMask) == 0:
result = true
when traceCollector:
cprintf("[ABOUT TO DESTROY] %p\n", cell)
else:
dec cell.rc, rcIncrement
# According to Lins it's correct to do nothing else here.
when traceCollector:
cprintf("[DeCREF] %p\n", cell)
proc GC_unref*[T](x: ref T) =
## New runtime only supports this operation for 'ref T'.
if nimDecRefIsLast(cast[pointer](x)):
# XXX this does NOT work for virtual destructors!
`=destroy`(x[])
nimRawDispose(cast[pointer](x), T.alignOf)
proc GC_ref*[T](x: ref T) =
## New runtime only supports this operation for 'ref T'.
if x != nil: nimIncRef(cast[pointer](x))
when not defined(gcOrc):
template GC_fullCollect* =
## Forces a full garbage collection pass. With ``--gc:arc`` a nop.
discard
template setupForeignThreadGc* =
## With ``--gc:arc`` a nop.
discard
template tearDownForeignThreadGc* =
## With ``--gc:arc`` a nop.
discard
proc isObj(obj: PNimTypeV2, subclass: cstring): bool {.compilerRtl, inl.} =
proc strstr(s, sub: cstring): cstring {.header: "<string.h>", importc.}
result = strstr(obj.name, subclass) != nil
proc chckObj(obj: PNimTypeV2, subclass: cstring) {.compilerRtl.} =
# checks if obj is of type subclass:
if not isObj(obj, subclass): sysFatal(ObjectConversionDefect, "invalid object conversion")
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