github.com/rsc/go@v0.0.0-20150416155037-e040fd465409/src/runtime/mem_windows.go (about)

     1  // Copyright 2010 The Go Authors.  All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import (
     8  	"unsafe"
     9  )
    10  
    11  const (
    12  	_MEM_COMMIT   = 0x1000
    13  	_MEM_RESERVE  = 0x2000
    14  	_MEM_DECOMMIT = 0x4000
    15  	_MEM_RELEASE  = 0x8000
    16  
    17  	_PAGE_READWRITE = 0x0004
    18  	_PAGE_NOACCESS  = 0x0001
    19  )
    20  
    21  //go:nosplit
    22  func sysAlloc(n uintptr, stat *uint64) unsafe.Pointer {
    23  	xadd64(stat, int64(n))
    24  	return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_COMMIT|_MEM_RESERVE, _PAGE_READWRITE))
    25  }
    26  
    27  func sysUnused(v unsafe.Pointer, n uintptr) {
    28  	r := stdcall3(_VirtualFree, uintptr(v), n, _MEM_DECOMMIT)
    29  	if r != 0 {
    30  		return
    31  	}
    32  
    33  	// Decommit failed. Usual reason is that we've merged memory from two different
    34  	// VirtualAlloc calls, and Windows will only let each VirtualFree handle pages from
    35  	// a single VirtualAlloc. It is okay to specify a subset of the pages from a single alloc,
    36  	// just not pages from multiple allocs. This is a rare case, arising only when we're
    37  	// trying to give memory back to the operating system, which happens on a time
    38  	// scale of minutes. It doesn't have to be terribly fast. Instead of extra bookkeeping
    39  	// on all our VirtualAlloc calls, try freeing successively smaller pieces until
    40  	// we manage to free something, and then repeat. This ends up being O(n log n)
    41  	// in the worst case, but that's fast enough.
    42  	for n > 0 {
    43  		small := n
    44  		for small >= 4096 && stdcall3(_VirtualFree, uintptr(v), small, _MEM_DECOMMIT) == 0 {
    45  			small /= 2
    46  			small &^= 4096 - 1
    47  		}
    48  		if small < 4096 {
    49  			throw("runtime: failed to decommit pages")
    50  		}
    51  		v = add(v, small)
    52  		n -= small
    53  	}
    54  }
    55  
    56  func sysUsed(v unsafe.Pointer, n uintptr) {
    57  	r := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
    58  	if r != uintptr(v) {
    59  		throw("runtime: failed to commit pages")
    60  	}
    61  
    62  	// Commit failed. See SysUnused.
    63  	for n > 0 {
    64  		small := n
    65  		for small >= 4096 && stdcall4(_VirtualAlloc, uintptr(v), small, _MEM_COMMIT, _PAGE_READWRITE) == 0 {
    66  			small /= 2
    67  			small &^= 4096 - 1
    68  		}
    69  		if small < 4096 {
    70  			throw("runtime: failed to decommit pages")
    71  		}
    72  		v = add(v, small)
    73  		n -= small
    74  	}
    75  }
    76  
    77  func sysFree(v unsafe.Pointer, n uintptr, stat *uint64) {
    78  	xadd64(stat, -int64(n))
    79  	r := stdcall3(_VirtualFree, uintptr(v), 0, _MEM_RELEASE)
    80  	if r == 0 {
    81  		throw("runtime: failed to release pages")
    82  	}
    83  }
    84  
    85  func sysFault(v unsafe.Pointer, n uintptr) {
    86  	// SysUnused makes the memory inaccessible and prevents its reuse
    87  	sysUnused(v, n)
    88  }
    89  
    90  func sysReserve(v unsafe.Pointer, n uintptr, reserved *bool) unsafe.Pointer {
    91  	*reserved = true
    92  	// v is just a hint.
    93  	// First try at v.
    94  	v = unsafe.Pointer(stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_RESERVE, _PAGE_READWRITE))
    95  	if v != nil {
    96  		return v
    97  	}
    98  
    99  	// Next let the kernel choose the address.
   100  	return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_RESERVE, _PAGE_READWRITE))
   101  }
   102  
   103  func sysMap(v unsafe.Pointer, n uintptr, reserved bool, stat *uint64) {
   104  	xadd64(stat, int64(n))
   105  	p := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
   106  	if p != uintptr(v) {
   107  		throw("runtime: cannot map pages in arena address space")
   108  	}
   109  }