forked from sjwhitworth/golearn
/
map.go
424 lines (368 loc) · 10.2 KB
/
map.go
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package edf
import (
"fmt"
mmap "github.com/Sentimentron/go-mmap"
"os"
"runtime"
"runtime/debug"
)
type edfMode int
const (
edfFileMode edfMode = iota
edfAnonMode
edfFreedMode
)
// EdfFile represents a mapped file on disk or
// and anonymous mapping for instance storage
type EdfFile struct {
f *os.File
m []mmap.Mmap
segmentSize uint64
pageSize uint64
mode edfMode
}
// GetPageSize returns the pageSize of an EdfFile
func (e *EdfFile) GetPageSize() uint64 {
return e.pageSize
}
// edfPosition represents a start and finish point
// within the mapping
type edfPosition struct {
Segment uint64
Byte uint64
}
// edfRange represents a start and an end segment
// mapped in an EdfFile and also the byte offsets
// within that segment
type edfRange struct {
Start edfPosition
End edfPosition
segmentSize uint64
}
// Size returns the size (in bytes) of a given edfRange
func (r *edfRange) Size() uint64 {
ret := uint64(r.End.Segment-r.Start.Segment) * r.segmentSize
ret += uint64(r.End.Byte - r.Start.Byte)
return ret
}
// edfCallFree is a half-baked finalizer called on garbage
// collection to ensure that the mapping gets freed
func edfCallFree(e *EdfFile) {
e.unmap(EDF_UNMAP_NOSYNC)
}
// EdfAnonMap maps the EdfFile structure into RAM
// IMPORTANT: everything's lost if unmapped
func EdfAnonMap() (*EdfFile, error) {
var err error
// Allocate return structure
ret := new(EdfFile)
// Create mapping references
ret.m = make([]mmap.Mmap, 0)
// Get the page size
pageSize := int64(os.Getpagesize())
// Segment size is the size of each mapped region
ret.pageSize = uint64(pageSize)
ret.segmentSize = uint64(EDF_LENGTH) * uint64(os.Getpagesize())
// Set the mode
ret.mode = edfAnonMode
// Allocate 4 pages initially
ret.truncate(4)
// Generate the header
ret.createHeader()
err = ret.writeInitialData()
// Make sure this gets unmapped on garbage collection
runtime.SetFinalizer(ret, edfCallFree)
return ret, err
}
// edfMap takes an os.File and returns an EdfMappedFile
// structure, which represents the mmap'd underlying file
//
// The `mode` parameter takes the following values
// EDF_CREATE: edfMap will truncate the file to the right length and write the correct header information
// EDF_READ_WRITE: edfMap will verify header information
// EDF_READ_ONLY: edfMap will verify header information
// IMPORTANT: EDF_LENGTH (edf.go) controls the size of the address
// space mapping. This means that the file can be truncated to the
// correct size without remapping. On 32-bit systems, this
// is set to 2GiB.
func edfMap(f *os.File, mode int) (*EdfFile, error) {
var err error
// Set up various things
ret := new(EdfFile)
ret.f = f
ret.m = make([]mmap.Mmap, 0)
// Figure out the flags
protFlags := mmap.PROT_READ
if mode == EDF_READ_WRITE || mode == EDF_CREATE {
protFlags |= mmap.PROT_WRITE
}
mapFlags := mmap.MAP_FILE | mmap.MAP_SHARED
// Get the page size
pageSize := int64(os.Getpagesize())
// Segment size is the size of each mapped region
ret.pageSize = uint64(pageSize)
ret.segmentSize = uint64(EDF_LENGTH) * uint64(os.Getpagesize())
// Map the file
for i := int64(0); i < EDF_SIZE; i += int64(EDF_LENGTH) * pageSize {
thisMapping, err := mmap.Map(f, i*pageSize, int(int64(EDF_LENGTH)*pageSize), protFlags, mapFlags)
if err != nil {
// TODO: cleanup
return nil, err
}
ret.m = append(ret.m, thisMapping)
}
// Verify or generate the header
if mode == EDF_READ_WRITE || mode == EDF_READ_ONLY {
err = ret.verifyHeader()
if err != nil {
return nil, err
}
} else if mode == EDF_CREATE {
err = ret.truncate(4)
if err != nil {
return nil, err
}
ret.createHeader()
err = ret.writeInitialData()
} else {
err = fmt.Errorf("Unrecognised flags")
}
// Make sure this gets unmapped on garbage collection
runtime.SetFinalizer(ret, edfCallFree)
// Set the mode
ret.mode = edfFileMode
return ret, err
}
// getByteRange returns the segment offset and range of
// two positions in the file.
func (e *EdfFile) getByteRange(byteStart uint64, byteEnd uint64) edfRange {
var ret edfRange
ret.Start.Segment = byteStart / e.segmentSize
ret.End.Segment = byteEnd / e.segmentSize
ret.Start.Byte = byteStart % e.segmentSize
ret.End.Byte = byteEnd % e.segmentSize
ret.segmentSize = e.segmentSize
return ret
}
// getPageRange returns the segment offset and range of
// two pages in the file.
func (e *EdfFile) getPageRange(pageStart uint64, pageEnd uint64) edfRange {
return e.getByteRange(pageStart*e.pageSize, pageEnd*e.pageSize+e.pageSize-1)
}
// verifyHeader checks that this version of Golearn can
// read the file presented.
func (e *EdfFile) verifyHeader() error {
// Check the magic bytes
diff := (e.m[0][0] ^ byte('G')) | (e.m[0][1] ^ byte('O'))
diff |= (e.m[0][2] ^ byte('L')) | (e.m[0][3] ^ byte('N'))
if diff != 0 {
return fmt.Errorf("Invalid magic bytes")
}
// Check the file version
version := uint32FromBytes(e.m[0][4:8])
if version != EDF_VERSION {
return fmt.Errorf("Unsupported version: %d", version)
}
// Check the page size
pageSize := uint32FromBytes(e.m[0][8:12])
if pageSize != uint32(os.Getpagesize()) {
return fmt.Errorf("Unsupported page size: (file: %d, system: %d", pageSize, os.Getpagesize())
}
return nil
}
// createHeader writes a valid header file into the file.
// Unexported since it can cause data loss.
func (e *EdfFile) createHeader() {
e.m[0][0] = byte('G')
e.m[0][1] = byte('O')
e.m[0][2] = byte('L')
e.m[0][3] = byte('N')
uint32ToBytes(EDF_VERSION, e.m[0][4:8])
uint32ToBytes(uint32(os.Getpagesize()), e.m[0][8:12])
e.sync()
}
// writeInitialData writes system thread information
func (e *EdfFile) writeInitialData() error {
var t thread
t.name = "SYSTEM"
t.id = 1
err := e.WriteThread(&t)
if err != nil {
return err
}
t.name = "FIXED"
t.id = 2
err = e.WriteThread(&t)
return err
}
// getThreadCount returns the number of threads in this file.
func (e *EdfFile) getThreadCount() uint32 {
// The number of threads is stored in bytes 12-16 in the header
return uint32FromBytes(e.m[0][12:])
}
// incrementThreadCount increments the record of the number
// of threads in this file
func (e *EdfFile) incrementThreadCount() uint32 {
cur := e.getThreadCount()
cur++
uint32ToBytes(cur, e.m[0][12:])
return cur
}
// GetThreads returns the thread identifier -> name map.
func (e *EdfFile) GetThreads() (map[uint32]string, error) {
ret := make(map[uint32]string)
count := e.getThreadCount()
// The starting block
block := uint64(1)
for {
// Decode the block offset
r := e.getPageRange(block, block)
if r.Start.Segment != r.End.Segment {
return nil, fmt.Errorf("thread range split across segments")
}
bytes := e.m[r.Start.Segment]
bytes = bytes[r.Start.Byte : r.End.Byte+1]
// The first 8 bytes say where to go next
block = uint64FromBytes(bytes)
bytes = bytes[8:]
for {
length := uint32FromBytes(bytes)
if length == 0 {
break
}
t := &thread{}
size := t.Deserialize(bytes)
bytes = bytes[size:]
ret[t.id] = t.name[0:len(t.name)]
}
// If next block offset is zero, no more threads to read
if block == 0 {
break
}
}
// Hey? What's wrong with you!
if len(ret) != int(count) {
return ret, fmt.Errorf("thread mismatch: %d/%d, indicates possible corruption", len(ret), count)
}
return ret, nil
}
// sync writes information to physical storage.
func (e *EdfFile) sync() error {
// Do nothing if we're mapped anonymously
if e.mode == edfAnonMode {
return nil
}
for _, m := range e.m {
err := m.Sync(mmap.MS_SYNC)
if err != nil {
return err
}
}
return nil
}
// truncate changes the size of the underlying file
// The size of the address space doesn't change.
func (e *EdfFile) truncateFile(size int64) error {
pageSize := int64(os.Getpagesize())
newSize := pageSize * size
// Synchronise
// e.sync()
// Double-check that we're not reducing file size
fileInfo, err := e.f.Stat()
if err != nil {
return err
}
if fileInfo.Size() > newSize {
return fmt.Errorf("Can't reduce file size!")
}
// Truncate the file
err = e.f.Truncate(newSize)
if err != nil {
return err
}
// Verify that the file is larger now than it was
fileInfo, err = e.f.Stat()
if err != nil {
return err
}
if fileInfo.Size() != newSize {
return fmt.Errorf("Truncation failed: %d, %d", fileInfo.Size(), newSize)
}
return err
}
func (e *EdfFile) truncateMem(size int64) error {
pageSize := int64(os.Getpagesize())
newSize := pageSize * size
currentSize := 0
for _, m := range e.m {
currentSize += len(m)
}
if int64(currentSize) > newSize {
return fmt.Errorf("Can't reduce size")
}
// Allocate some more memory
for i := uint64(currentSize); i < uint64(newSize); i += e.segmentSize {
newMap := make([]byte, e.segmentSize)
e.m = append(e.m, newMap)
}
return nil
}
func (e *EdfFile) truncate(size int64) error {
if e.mode == edfAnonMode {
return e.truncateMem(size)
} else if e.mode == edfFileMode {
return e.truncateFile(size)
}
panic("Unsupported")
}
// unmap unlinks the EdfFile from the address space.
// EDF_UNMAP_NOSYNC skips calling Sync() on the underlying
// file before this happens.
// IMPORTANT: attempts to use this mapping after unmap() is
// called will result in crashes.
func (e *EdfFile) unmap(flags int) error {
var ret error
// Check if the file has already been freed
if e.mode == edfFreedMode {
fmt.Fprintln(os.Stderr, "Potential double-free")
debug.PrintStack()
return nil
} else if e.mode == edfAnonMode {
// If it's anonymous, don't do anything
e.m = nil
e.mode = edfFreedMode
return nil
}
// Sync the file
if flags != EDF_UNMAP_NOSYNC {
e.sync()
}
e.mode = edfFreedMode
// Unmap the file
for _, m := range e.m {
err := m.Unmap()
if err != nil {
ret = err
}
}
return ret
}
// ResolveRange returns a slice of byte slices representing
// the underlying memory referenced by edfRange.
//
// WARNING: slow.
func (e *EdfFile) ResolveRange(r edfRange) [][]byte {
var ret [][]byte
segCounter := 0
for segment := r.Start.Segment; segment <= r.End.Segment; segment++ {
if segment == r.Start.Segment {
ret = append(ret, e.m[segment][r.Start.Byte:])
} else if segment == r.End.Segment {
ret = append(ret, e.m[segment][:r.End.Byte+1])
} else {
ret = append(ret, e.m[segment])
}
segCounter++
}
return ret
}