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| 3bd1f2 | 1 | // Copyright 2016 Tom Thorogood. All rights reserved. |
| Z | 2 | // Use of this source code is governed by a |
| 3 | // Modified BSD License license that can be found in | |
| 4 | // the LICENSE file. | |
| 5 | ||
| 6 | package shm | |
| 7 | ||
| 8 | import ( | |
| 9 | "io" | |
| 10 | "sync/atomic" | |
| 11 | "unsafe" | |
| 12 | ||
| a0123f | 13 | "golang.org/x/sys/unix" |
| 3bd1f2 | 14 | ) |
| Z | 15 | |
| 16 | const ( | |
| 17 | eofFlagIndex = 0 | |
| 18 | eofFlagMask = 0x01 | |
| 19 | ) | |
| 20 | ||
| 21 | type Buffer struct { | |
| 22 | block *sharedBlock | |
| 23 | write bool | |
| 24 | ||
| 25 | Data []byte | |
| 26 | Flags *[blockFlagsSize]byte | |
| 27 | } | |
| 28 | ||
| 29 | type ReadWriteCloser struct { | |
| 30 | name string | |
| 31 | ||
| 32 | data []byte | |
| 33 | readShared *sharedMem | |
| 34 | writeShared *sharedMem | |
| 35 | size uint64 | |
| 36 | fullBlockSize uint64 | |
| 37 | ||
| 38 | // Must be accessed using atomic operations | |
| 39 | Flags *[sharedFlagsSize]uint32 | |
| 40 | ||
| 41 | closed uint32 | |
| 42 | } | |
| 43 | ||
| 44 | func (rw *ReadWriteCloser) Close() error { | |
| 45 | if !atomic.CompareAndSwapUint32(&rw.closed, 0, 1) { | |
| 46 | return nil | |
| 47 | } | |
| 48 | ||
| 49 | // finish all sends before close! | |
| 50 | ||
| 51 | return unix.Munmap(rw.data) | |
| 52 | } | |
| 53 | ||
| 54 | // Name returns the name of the shared memory. | |
| 55 | func (rw *ReadWriteCloser) Name() string { | |
| 56 | return rw.name | |
| 57 | } | |
| 58 | ||
| 59 | // Read | |
| 60 | ||
| 61 | func (rw *ReadWriteCloser) Read(p []byte) (n int, err error) { | |
| 62 | buf, err := rw.GetReadBuffer() | |
| 63 | if err != nil { | |
| 64 | return 0, err | |
| 65 | } | |
| 66 | ||
| 67 | n = copy(p, buf.Data) | |
| 68 | isEOF := buf.Flags[eofFlagIndex]&eofFlagMask != 0 | |
| 69 | ||
| 70 | if err = rw.SendReadBuffer(buf); err != nil { | |
| 71 | return n, err | |
| 72 | } | |
| 73 | ||
| 74 | if isEOF { | |
| 75 | return n, io.EOF | |
| 76 | } | |
| 77 | ||
| 78 | return n, nil | |
| 79 | } | |
| 80 | ||
| 81 | func (rw *ReadWriteCloser) WriteTo(w io.Writer) (n int64, err error) { | |
| 82 | for { | |
| 83 | buf, err := rw.GetReadBuffer() | |
| 84 | if err != nil { | |
| 85 | return n, err | |
| 86 | } | |
| 87 | ||
| 88 | nn, err := w.Write(buf.Data) | |
| 89 | n += int64(nn) | |
| 90 | ||
| 91 | isEOF := buf.Flags[eofFlagIndex]&eofFlagMask != 0 | |
| 92 | ||
| 93 | if putErr := rw.SendReadBuffer(buf); putErr != nil { | |
| 94 | return n, putErr | |
| 95 | } | |
| 96 | ||
| 97 | if err != nil || isEOF { | |
| 98 | return n, err | |
| 99 | } | |
| 100 | } | |
| 101 | } | |
| 102 | ||
| 103 | func (rw *ReadWriteCloser) GetReadBuffer() (Buffer, error) { | |
| 104 | if atomic.LoadUint32(&rw.closed) != 0 { | |
| 105 | return Buffer{}, io.ErrClosedPipe | |
| 106 | } | |
| 107 | ||
| 108 | var block *sharedBlock | |
| 109 | ||
| 110 | blocks := uintptr(unsafe.Pointer(rw.readShared)) + sharedHeaderSize | |
| 111 | ||
| 112 | for { | |
| 113 | blockIndex := atomic.LoadUint32((*uint32)(&rw.readShared.ReadStart)) | |
| 114 | if blockIndex > uint32(rw.readShared.BlockCount) { | |
| 115 | return Buffer{}, ErrInvalidSharedMemory | |
| 116 | } | |
| 117 | ||
| 118 | block = (*sharedBlock)(unsafe.Pointer(blocks + uintptr(uint64(blockIndex)*rw.fullBlockSize))) | |
| 119 | ||
| 120 | if blockIndex == atomic.LoadUint32((*uint32)(&rw.readShared.WriteEnd)) { | |
| a0123f | 121 | if err := ((*Semaphore)(&rw.readShared.SemSignal)).Wait(); err != nil { |
| 3bd1f2 | 122 | return Buffer{}, err |
| Z | 123 | } |
| 124 | ||
| 125 | continue | |
| 126 | } | |
| 127 | ||
| 128 | if atomic.CompareAndSwapUint32((*uint32)(&rw.readShared.ReadStart), blockIndex, uint32(block.Next)) { | |
| 129 | break | |
| 130 | } | |
| 131 | } | |
| 132 | ||
| 133 | data := (*[1 << 30]byte)(unsafe.Pointer(uintptr(unsafe.Pointer(block)) + blockHeaderSize)) | |
| 134 | flags := (*[len(block.Flags)]byte)(unsafe.Pointer(&block.Flags[0])) | |
| 135 | return Buffer{ | |
| 136 | block: block, | |
| 137 | ||
| 138 | Data: data[:block.Size:rw.readShared.BlockSize], | |
| 139 | Flags: flags, | |
| 140 | }, nil | |
| 141 | } | |
| 142 | ||
| 143 | func (rw *ReadWriteCloser) SendReadBuffer(buf Buffer) error { | |
| 144 | if atomic.LoadUint32(&rw.closed) != 0 { | |
| 145 | return io.ErrClosedPipe | |
| 146 | } | |
| 147 | ||
| 148 | if buf.write { | |
| 149 | return ErrInvalidBuffer | |
| 150 | } | |
| 151 | ||
| 152 | block := buf.block | |
| 153 | ||
| 154 | atomic.StoreUint32((*uint32)(&block.DoneRead), 1) | |
| 155 | ||
| 156 | blocks := uintptr(unsafe.Pointer(rw.readShared)) + sharedHeaderSize | |
| 157 | ||
| 158 | for { | |
| 159 | blockIndex := atomic.LoadUint32((*uint32)(&rw.readShared.ReadEnd)) | |
| 160 | if blockIndex > uint32(rw.readShared.BlockCount) { | |
| 161 | return ErrInvalidSharedMemory | |
| 162 | } | |
| 163 | ||
| 164 | block = (*sharedBlock)(unsafe.Pointer(blocks + uintptr(uint64(blockIndex)*rw.fullBlockSize))) | |
| 165 | ||
| 166 | if !atomic.CompareAndSwapUint32((*uint32)(&block.DoneRead), 1, 0) { | |
| 167 | return nil | |
| 168 | } | |
| 169 | ||
| 170 | atomic.CompareAndSwapUint32((*uint32)(&rw.readShared.ReadEnd), blockIndex, uint32(block.Next)) | |
| 171 | ||
| 172 | if uint32(block.Prev) == atomic.LoadUint32((*uint32)(&rw.readShared.WriteStart)) { | |
| a0123f | 173 | if err := ((*Semaphore)(&rw.readShared.SemAvail)).Post(); err != nil { |
| 3bd1f2 | 174 | return err |
| Z | 175 | } |
| 176 | } | |
| 177 | } | |
| 178 | } | |
| 179 | ||
| 180 | // Write | |
| 181 | ||
| 182 | func (rw *ReadWriteCloser) Write(p []byte) (n int, err error) { | |
| 183 | buf, err := rw.GetWriteBuffer() | |
| 184 | if err != nil { | |
| 185 | return 0, err | |
| 186 | } | |
| 187 | ||
| 188 | n = copy(buf.Data[:cap(buf.Data)], p) | |
| 189 | buf.Data = buf.Data[:n] | |
| 190 | ||
| 191 | buf.Flags[eofFlagIndex] |= eofFlagMask | |
| 192 | ||
| 193 | _, err = rw.SendWriteBuffer(buf) | |
| 194 | return n, err | |
| 195 | } | |
| 196 | ||
| 197 | func (rw *ReadWriteCloser) ReadFrom(r io.Reader) (n int64, err error) { | |
| 198 | for { | |
| 199 | buf, err := rw.GetWriteBuffer() | |
| 200 | if err != nil { | |
| 201 | return n, err | |
| 202 | } | |
| 203 | ||
| 204 | nn, err := r.Read(buf.Data[:cap(buf.Data)]) | |
| 205 | buf.Data = buf.Data[:nn] | |
| 206 | n += int64(nn) | |
| 207 | ||
| 208 | if err == io.EOF { | |
| 209 | buf.Flags[eofFlagIndex] |= eofFlagMask | |
| 210 | } else { | |
| 211 | buf.Flags[eofFlagIndex] &^= eofFlagMask | |
| 212 | } | |
| 213 | ||
| 214 | if _, putErr := rw.SendWriteBuffer(buf); putErr != nil { | |
| 215 | return n, err | |
| 216 | } | |
| 217 | ||
| 218 | if err == io.EOF { | |
| 219 | return n, nil | |
| 220 | } else if err != nil { | |
| 221 | return n, err | |
| 222 | } | |
| 223 | } | |
| 224 | } | |
| 225 | ||
| 226 | func (rw *ReadWriteCloser) GetWriteBuffer() (Buffer, error) { | |
| 227 | if atomic.LoadUint32(&rw.closed) != 0 { | |
| 228 | return Buffer{}, io.ErrClosedPipe | |
| 229 | } | |
| 230 | ||
| 231 | var block *sharedBlock | |
| 232 | ||
| 233 | blocks := uintptr(unsafe.Pointer(rw.writeShared)) + sharedHeaderSize | |
| 234 | ||
| 235 | for { | |
| 236 | blockIndex := atomic.LoadUint32((*uint32)(&rw.writeShared.WriteStart)) | |
| 237 | if blockIndex > uint32(rw.writeShared.BlockCount) { | |
| 238 | return Buffer{}, ErrInvalidSharedMemory | |
| 239 | } | |
| 240 | ||
| 241 | block = (*sharedBlock)(unsafe.Pointer(blocks + uintptr(uint64(blockIndex)*rw.fullBlockSize))) | |
| 242 | ||
| 243 | if uint32(block.Next) == atomic.LoadUint32((*uint32)(&rw.writeShared.ReadEnd)) { | |
| a0123f | 244 | if err := ((*Semaphore)(&rw.writeShared.SemAvail)).Wait(); err != nil { |
| 3bd1f2 | 245 | return Buffer{}, err |
| Z | 246 | } |
| 247 | ||
| 248 | continue | |
| 249 | } | |
| 250 | ||
| 251 | if atomic.CompareAndSwapUint32((*uint32)(&rw.writeShared.WriteStart), blockIndex, uint32(block.Next)) { | |
| 252 | break | |
| 253 | } | |
| 254 | } | |
| 255 | ||
| 256 | data := (*[1 << 30]byte)(unsafe.Pointer(uintptr(unsafe.Pointer(block)) + blockHeaderSize)) | |
| 257 | flags := (*[len(block.Flags)]byte)(unsafe.Pointer(&block.Flags[0])) | |
| 258 | return Buffer{ | |
| 259 | block: block, | |
| 260 | write: true, | |
| 261 | ||
| 262 | Data: data[:0:rw.writeShared.BlockSize], | |
| 263 | Flags: flags, | |
| 264 | }, nil | |
| 265 | } | |
| 266 | ||
| 267 | func (rw *ReadWriteCloser) SendWriteBuffer(buf Buffer) (n int, err error) { | |
| 268 | if atomic.LoadUint32(&rw.closed) != 0 { | |
| 269 | return 0, io.ErrClosedPipe | |
| 270 | } | |
| 271 | ||
| 272 | if !buf.write { | |
| 273 | return 0, ErrInvalidBuffer | |
| 274 | } | |
| 275 | ||
| 276 | block := buf.block | |
| 277 | ||
| 278 | *(*uint64)(&block.Size) = uint64(len(buf.Data)) | |
| 279 | ||
| 280 | atomic.StoreUint32((*uint32)(&block.DoneWrite), 1) | |
| 281 | ||
| 282 | blocks := uintptr(unsafe.Pointer(rw.writeShared)) + sharedHeaderSize | |
| 283 | ||
| 284 | for { | |
| 285 | blockIndex := atomic.LoadUint32((*uint32)(&rw.writeShared.WriteEnd)) | |
| 286 | if blockIndex > uint32(rw.writeShared.BlockCount) { | |
| 287 | return len(buf.Data), ErrInvalidSharedMemory | |
| 288 | } | |
| 289 | ||
| 290 | block = (*sharedBlock)(unsafe.Pointer(blocks + uintptr(uint64(blockIndex)*rw.fullBlockSize))) | |
| 291 | ||
| 292 | if !atomic.CompareAndSwapUint32((*uint32)(&block.DoneWrite), 1, 0) { | |
| 293 | return len(buf.Data), nil | |
| 294 | } | |
| 295 | ||
| 296 | atomic.CompareAndSwapUint32((*uint32)(&rw.writeShared.WriteEnd), blockIndex, uint32(block.Next)) | |
| 297 | ||
| 298 | if blockIndex == atomic.LoadUint32((*uint32)(&rw.writeShared.ReadStart)) { | |
| a0123f | 299 | if err := ((*Semaphore)(&rw.writeShared.SemSignal)).Post(); err != nil { |
| 3bd1f2 | 300 | return len(buf.Data), err |
| Z | 301 | } |
| 302 | } | |
| 303 | } | |
| 304 | } | |
