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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Fixed-size object allocator. Returned memory is not zeroed.
//
// See malloc.h for overview.
package runtime
import "unsafe"
// FixAlloc is a simple free-list allocator for fixed size objects.
// Malloc uses a FixAlloc wrapped around sysAlloc to manages its
// MCache and MSpan objects.
//
// Memory returned by FixAlloc_Alloc is not zeroed.
// The caller is responsible for locking around FixAlloc calls.
// Callers can keep state in the object but the first word is
// smashed by freeing and reallocating.
type fixalloc struct {
size uintptr
first unsafe.Pointer // go func(unsafe.pointer, unsafe.pointer); f(arg, p) called first time p is returned
arg unsafe.Pointer
list *mlink
chunk *byte
nchunk uint32
inuse uintptr // in-use bytes now
stat *uint64
}
// A generic linked list of blocks. (Typically the block is bigger than sizeof(MLink).)
// Since assignments to mlink.next will result in a write barrier being preformed
// this can not be used by some of the internal GC structures. For example when
// the sweeper is placing an unmarked object on the free list it does not want the
// write barrier to be called since that could result in the object being reachable.
type mlink struct {
next *mlink
}
// Initialize f to allocate objects of the given size,
// using the allocator to obtain chunks of memory.
func fixAlloc_Init(f *fixalloc, size uintptr, first func(unsafe.Pointer, unsafe.Pointer), arg unsafe.Pointer, stat *uint64) {
f.size = size
f.first = *(*unsafe.Pointer)(unsafe.Pointer(&first))
f.arg = arg
f.list = nil
f.chunk = nil
f.nchunk = 0
f.inuse = 0
f.stat = stat
}
func fixAlloc_Alloc(f *fixalloc) unsafe.Pointer {
if f.size == 0 {
print("runtime: use of FixAlloc_Alloc before FixAlloc_Init\n")
throw("runtime: internal error")
}
if f.list != nil {
v := unsafe.Pointer(f.list)
f.list = f.list.next
f.inuse += f.size
return v
}
if uintptr(f.nchunk) < f.size {
f.chunk = (*uint8)(persistentalloc(_FixAllocChunk, 0, f.stat))
f.nchunk = _FixAllocChunk
}
v := (unsafe.Pointer)(f.chunk)
if f.first != nil {
fn := *(*func(unsafe.Pointer, unsafe.Pointer))(unsafe.Pointer(&f.first))
fn(f.arg, v)
}
f.chunk = (*byte)(add(unsafe.Pointer(f.chunk), f.size))
f.nchunk -= uint32(f.size)
f.inuse += f.size
return v
}
func fixAlloc_Free(f *fixalloc, p unsafe.Pointer) {
f.inuse -= f.size
v := (*mlink)(p)
v.next = f.list
f.list = v
}
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