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// Copyright 2010 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.
package runtime
import (
"unsafe"
)
const (
_MEM_COMMIT = 0x1000
_MEM_RESERVE = 0x2000
_MEM_DECOMMIT = 0x4000
_MEM_RELEASE = 0x8000
_PAGE_READWRITE = 0x0004
_PAGE_NOACCESS = 0x0001
)
//go:cgo_import_dynamic runtime._VirtualAlloc VirtualAlloc "kernel32.dll"
//go:cgo_import_dynamic runtime._VirtualFree VirtualFree "kernel32.dll"
//go:cgo_import_dynamic runtime._VirtualProtect VirtualProtect "kernel32.dll"
var (
_VirtualAlloc,
_VirtualFree,
_VirtualProtect stdFunction
)
//go:nosplit
func sysAlloc(n uintptr, stat *uint64) unsafe.Pointer {
xadd64(stat, int64(n))
return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_COMMIT|_MEM_RESERVE, _PAGE_READWRITE))
}
func sysUnused(v unsafe.Pointer, n uintptr) {
r := stdcall3(_VirtualFree, uintptr(v), n, _MEM_DECOMMIT)
if r != 0 {
return
}
// Decommit failed. Usual reason is that we've merged memory from two different
// VirtualAlloc calls, and Windows will only let each VirtualFree handle pages from
// a single VirtualAlloc. It is okay to specify a subset of the pages from a single alloc,
// just not pages from multiple allocs. This is a rare case, arising only when we're
// trying to give memory back to the operating system, which happens on a time
// scale of minutes. It doesn't have to be terribly fast. Instead of extra bookkeeping
// on all our VirtualAlloc calls, try freeing successively smaller pieces until
// we manage to free something, and then repeat. This ends up being O(n log n)
// in the worst case, but that's fast enough.
for n > 0 {
small := n
for small >= 4096 && stdcall3(_VirtualFree, uintptr(v), small, _MEM_DECOMMIT) == 0 {
small /= 2
small &^= 4096 - 1
}
if small < 4096 {
gothrow("runtime: failed to decommit pages")
}
v = add(v, small)
n -= small
}
}
func sysUsed(v unsafe.Pointer, n uintptr) {
r := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
if r != uintptr(v) {
gothrow("runtime: failed to commit pages")
}
// Commit failed. See SysUnused.
for n > 0 {
small := n
for small >= 4096 && stdcall4(_VirtualAlloc, uintptr(v), small, _MEM_COMMIT, _PAGE_READWRITE) == 0 {
small /= 2
small &^= 4096 - 1
}
if small < 4096 {
gothrow("runtime: failed to decommit pages")
}
v = add(v, small)
n -= small
}
}
func sysFree(v unsafe.Pointer, n uintptr, stat *uint64) {
xadd64(stat, -int64(n))
r := stdcall3(_VirtualFree, uintptr(v), 0, _MEM_RELEASE)
if r == 0 {
gothrow("runtime: failed to release pages")
}
}
func sysFault(v unsafe.Pointer, n uintptr) {
// SysUnused makes the memory inaccessible and prevents its reuse
sysUnused(v, n)
}
func sysReserve(v unsafe.Pointer, n uintptr, reserved *bool) unsafe.Pointer {
*reserved = true
// v is just a hint.
// First try at v.
v = unsafe.Pointer(stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_RESERVE, _PAGE_READWRITE))
if v != nil {
return v
}
// Next let the kernel choose the address.
return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_RESERVE, _PAGE_READWRITE))
}
func sysMap(v unsafe.Pointer, n uintptr, reserved bool, stat *uint64) {
xadd64(stat, int64(n))
p := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
if p != uintptr(v) {
gothrow("runtime: cannot map pages in arena address space")
}
}
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