github.com/ltltlt/go-source-code@v0.0.0-20190830023027-95be009773aa/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  	_ERROR_NOT_ENOUGH_MEMORY = 8
    21  	_ERROR_COMMITMENT_LIMIT  = 1455
    22  )
    23  
    24  // Don't split the stack as this function may be invoked without a valid G,
    25  // which prevents us from allocating more stack.
    26  //go:nosplit
    27  func sysAlloc(n uintptr, sysStat *uint64) unsafe.Pointer {
    28  	mSysStatInc(sysStat, n)
    29  	return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_COMMIT|_MEM_RESERVE, _PAGE_READWRITE))
    30  }
    31  
    32  func sysUnused(v unsafe.Pointer, n uintptr) {
    33  	r := stdcall3(_VirtualFree, uintptr(v), n, _MEM_DECOMMIT)
    34  	if r != 0 {
    35  		return
    36  	}
    37  
    38  	// Decommit failed. Usual reason is that we've merged memory from two different
    39  	// VirtualAlloc calls, and Windows will only let each VirtualFree handle pages from
    40  	// a single VirtualAlloc. It is okay to specify a subset of the pages from a single alloc,
    41  	// just not pages from multiple allocs. This is a rare case, arising only when we're
    42  	// trying to give memory back to the operating system, which happens on a time
    43  	// scale of minutes. It doesn't have to be terribly fast. Instead of extra bookkeeping
    44  	// on all our VirtualAlloc calls, try freeing successively smaller pieces until
    45  	// we manage to free something, and then repeat. This ends up being O(n log n)
    46  	// in the worst case, but that's fast enough.
    47  	for n > 0 {
    48  		small := n
    49  		for small >= 4096 && stdcall3(_VirtualFree, uintptr(v), small, _MEM_DECOMMIT) == 0 {
    50  			small /= 2
    51  			small &^= 4096 - 1
    52  		}
    53  		if small < 4096 {
    54  			print("runtime: VirtualFree of ", small, " bytes failed with errno=", getlasterror(), "\n")
    55  			throw("runtime: failed to decommit pages")
    56  		}
    57  		v = add(v, small)
    58  		n -= small
    59  	}
    60  }
    61  
    62  func sysUsed(v unsafe.Pointer, n uintptr) {
    63  	r := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
    64  	if r == uintptr(v) {
    65  		return
    66  	}
    67  
    68  	// Commit failed. See SysUnused.
    69  	for n > 0 {
    70  		small := n
    71  		for small >= 4096 && stdcall4(_VirtualAlloc, uintptr(v), small, _MEM_COMMIT, _PAGE_READWRITE) == 0 {
    72  			small /= 2
    73  			small &^= 4096 - 1
    74  		}
    75  		if small < 4096 {
    76  			print("runtime: VirtualAlloc of ", small, " bytes failed with errno=", getlasterror(), "\n")
    77  			throw("runtime: failed to commit pages")
    78  		}
    79  		v = add(v, small)
    80  		n -= small
    81  	}
    82  }
    83  
    84  // Don't split the stack as this function may be invoked without a valid G,
    85  // which prevents us from allocating more stack.
    86  //go:nosplit
    87  func sysFree(v unsafe.Pointer, n uintptr, sysStat *uint64) {
    88  	mSysStatDec(sysStat, n)
    89  	r := stdcall3(_VirtualFree, uintptr(v), 0, _MEM_RELEASE)
    90  	if r == 0 {
    91  		print("runtime: VirtualFree of ", n, " bytes failed with errno=", getlasterror(), "\n")
    92  		throw("runtime: failed to release pages")
    93  	}
    94  }
    95  
    96  func sysFault(v unsafe.Pointer, n uintptr) {
    97  	// SysUnused makes the memory inaccessible and prevents its reuse
    98  	sysUnused(v, n)
    99  }
   100  
   101  func sysReserve(v unsafe.Pointer, n uintptr, reserved *bool) unsafe.Pointer {
   102  	*reserved = true
   103  	// v is just a hint.
   104  	// First try at v.
   105  	v = unsafe.Pointer(stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_RESERVE, _PAGE_READWRITE))
   106  	if v != nil {
   107  		return v
   108  	}
   109  
   110  	// Next let the kernel choose the address.
   111  	return unsafe.Pointer(stdcall4(_VirtualAlloc, 0, n, _MEM_RESERVE, _PAGE_READWRITE))
   112  }
   113  
   114  func sysMap(v unsafe.Pointer, n uintptr, reserved bool, sysStat *uint64) {
   115  	mSysStatInc(sysStat, n)
   116  	p := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
   117  	if p != uintptr(v) {
   118  		errno := getlasterror()
   119  		print("runtime: VirtualAlloc of ", n, " bytes failed with errno=", errno, "\n")
   120  		switch errno {
   121  		case _ERROR_NOT_ENOUGH_MEMORY, _ERROR_COMMITMENT_LIMIT:
   122  			throw("out of memory")
   123  		default:
   124  			throw("runtime: cannot map pages in arena address space")
   125  		}
   126  	}
   127  }