60 *
61 *
62 * @author Mark Reinhold
63 * @author JSR-51 Expert Group
64 * @since 1.4
65 */
66
67 public abstract class MappedByteBuffer
68 extends ByteBuffer
69 {
70
71 // This is a little bit backwards: By rights MappedByteBuffer should be a
72 // subclass of DirectByteBuffer, but to keep the spec clear and simple, and
73 // for optimization purposes, it's easier to do it the other way around.
74 // This works because DirectByteBuffer is a package-private class.
75
76 // For mapped buffers, a FileDescriptor that may be used for mapping
77 // operations if valid; null if the buffer is not mapped.
78 private final FileDescriptor fd;
79
80 // This should only be invoked by the DirectByteBuffer constructors
81 //
82 MappedByteBuffer(int mark, int pos, int lim, int cap, // package-private
83 FileDescriptor fd)
84 {
85 super(mark, pos, lim, cap);
86 this.fd = fd;
87 }
88
89 MappedByteBuffer(int mark, int pos, int lim, int cap) { // package-private
90 super(mark, pos, lim, cap);
91 this.fd = null;
92 }
93
94 // Returns the distance (in bytes) of the buffer from the page aligned address
95 // of the mapping. Computed each time to avoid storing in every direct buffer.
96 private long mappingOffset() {
97 int ps = Bits.pageSize();
98 long offset = address % ps;
99 return (offset >= 0) ? offset : (ps + offset);
100 }
101
102 private long mappingAddress(long mappingOffset) {
103 return address - mappingOffset;
104 }
105
106 private long mappingLength(long mappingOffset) {
107 return (long)capacity() + mappingOffset;
108 }
109
110 /**
111 * Tells whether or not this buffer's content is resident in physical
112 * memory.
113 *
114 * <p> A return value of {@code true} implies that it is highly likely
115 * that all of the data in this buffer is resident in physical memory and
116 * may therefore be accessed without incurring any virtual-memory page
117 * faults or I/O operations. A return value of {@code false} does not
118 * necessarily imply that the buffer's content is not resident in physical
119 * memory.
120 *
121 * <p> The returned value is a hint, rather than a guarantee, because the
122 * underlying operating system may have paged out some of the buffer's data
123 * by the time that an invocation of this method returns. </p>
124 *
125 * @return {@code true} if it is likely that this buffer's content
126 * is resident in physical memory
127 */
128 public final boolean isLoaded() {
129 if (fd == null) {
130 return true;
131 }
132 if ((address == 0) || (capacity() == 0))
133 return true;
134 long offset = mappingOffset();
135 long length = mappingLength(offset);
136 return isLoaded0(mappingAddress(offset), length, Bits.pageCount(length));
137 }
138
139 // not used, but a potential target for a store, see load() for details.
140 private static byte unused;
141
142 /**
143 * Loads this buffer's content into physical memory.
144 *
145 * <p> This method makes a best effort to ensure that, when it returns,
146 * this buffer's content is resident in physical memory. Invoking this
147 * method may cause some number of page faults and I/O operations to
148 * occur. </p>
149 *
150 * @return This buffer
151 */
152 public final MappedByteBuffer load() {
153 if (fd == null) {
154 return this;
155 }
156 if ((address == 0) || (capacity() == 0))
157 return this;
158 long offset = mappingOffset();
159 long length = mappingLength(offset);
160 load0(mappingAddress(offset), length);
161
162 // Read a byte from each page to bring it into memory. A checksum
163 // is computed as we go along to prevent the compiler from otherwise
164 // considering the loop as dead code.
165 Unsafe unsafe = Unsafe.getUnsafe();
166 int ps = Bits.pageSize();
167 int count = Bits.pageCount(length);
168 long a = mappingAddress(offset);
169 byte x = 0;
170 try {
171 for (int i=0; i<count; i++) {
172 // TODO consider changing to getByteOpaque thus avoiding
173 // dead code elimination and the need to calculate a checksum
174 x ^= unsafe.getByte(a);
175 a += ps;
185
186 /**
187 * Forces any changes made to this buffer's content to be written to the
188 * storage device containing the mapped file.
189 *
190 * <p> If the file mapped into this buffer resides on a local storage
191 * device then when this method returns it is guaranteed that all changes
192 * made to the buffer since it was created, or since this method was last
193 * invoked, will have been written to that device.
194 *
195 * <p> If the file does not reside on a local device then no such guarantee
196 * is made.
197 *
198 * <p> If this buffer was not mapped in read/write mode ({@link
199 * java.nio.channels.FileChannel.MapMode#READ_WRITE}) then invoking this
200 * method has no effect. </p>
201 *
202 * @return This buffer
203 */
204 public final MappedByteBuffer force() {
205 if (fd == null) {
206 return this;
207 }
208 if ((address != 0) && (capacity() != 0)) {
209 long offset = mappingOffset();
210 force0(fd, mappingAddress(offset), mappingLength(offset));
211 }
212 return this;
213 }
214
215 private native boolean isLoaded0(long address, long length, int pageCount);
216 private native void load0(long address, long length);
217 private native void force0(FileDescriptor fd, long address, long length);
218
219 // -- Covariant return type overrides
220
221 /**
222 * {@inheritDoc}
223 */
224 @Override
225 public final MappedByteBuffer position(int newPosition) {
226 super.position(newPosition);
227 return this;
228 }
229
230 /**
|
60 *
61 *
62 * @author Mark Reinhold
63 * @author JSR-51 Expert Group
64 * @since 1.4
65 */
66
67 public abstract class MappedByteBuffer
68 extends ByteBuffer
69 {
70
71 // This is a little bit backwards: By rights MappedByteBuffer should be a
72 // subclass of DirectByteBuffer, but to keep the spec clear and simple, and
73 // for optimization purposes, it's easier to do it the other way around.
74 // This works because DirectByteBuffer is a package-private class.
75
76 // For mapped buffers, a FileDescriptor that may be used for mapping
77 // operations if valid; null if the buffer is not mapped.
78 private final FileDescriptor fd;
79
80 // A flag true if this buffer is mapped against persistent memory
81 // via a call to FileChannel.map_persistent and false if it is
82 // some other sort of file mapped via a call to FileChannel.map.
83 // this flag only determines the behaviour of force operations.
84 private final boolean isPersistent;
85
86 // This should only be invoked by the DirectByteBuffer constructors
87 //
88 MappedByteBuffer(int mark, int pos, int lim, int cap, // package-private
89 FileDescriptor fd, boolean isPersistent) {
90 super(mark, pos, lim, cap);
91 this.fd = fd;
92 this.isPersistent = isPersistent;
93 }
94
95 MappedByteBuffer(int mark, int pos, int lim, int cap, // package-private
96 boolean isPersistent) {
97 super(mark, pos, lim, cap);
98 this.fd = null;
99 this.isPersistent = isPersistent;
100 }
101
102 MappedByteBuffer(int mark, int pos, int lim, int cap) { // package-private
103 super(mark, pos, lim, cap);
104 this.fd = null;
105 this.isPersistent = false;
106 }
107
108 // Returns the distance (in bytes) of the buffer from the page aligned address
109 // of the mapping. Computed each time to avoid storing in every direct buffer.
110 private long mappingOffset() {
111 int ps = Bits.pageSize();
112 long offset = address % ps;
113 return (offset >= 0) ? offset : (ps + offset);
114 }
115
116 private long mappingAddress(long mappingOffset) {
117 return address - mappingOffset;
118 }
119
120 private long mappingLength(long mappingOffset) {
121 return (long)capacity() + mappingOffset;
122 }
123
124 /**
125 * Tells whether this buffer was mapped against persistent memory
126 * by calling {@link java.nio.channels.FileChannel#map_persistent
127 * FileChannel.map_persistent} or mapped against some other form
128 * of device file using {@link java.nio.channels.FileChannel#map
129 * FileChannel.map}.
130 *
131 * @return true if the file was mapped using {@link
132 * java.nio.channels.FileChannel#map_persistent
133 * FileChannel.map_persistent} otherwise false.
134 */
135 public boolean isPersistent() {
136 return isPersistent;
137 }
138
139 /**
140 * Tells whether or not this buffer's content is resident in physical
141 * memory.
142 *
143 * <p> A return value of {@code true} implies that it is highly likely
144 * that all of the data in this buffer is resident in physical memory and
145 * may therefore be accessed without incurring any virtual-memory page
146 * faults or I/O operations. A return value of {@code false} does not
147 * necessarily imply that the buffer's content is not resident in physical
148 * memory.
149 *
150 * <p> The returned value is a hint, rather than a guarantee, because the
151 * underlying operating system may have paged out some of the buffer's data
152 * by the time that an invocation of this method returns. </p>
153 *
154 * @return {@code true} if it is likely that this buffer's content
155 * is resident in physical memory
156 */
157 public final boolean isLoaded() {
158 if (fd == null) {
159 return true;
160 }
161 // a persistent mapped buffer is always loaded
162 if (isPersistent()) {
163 return true;
164 }
165 if ((address == 0) || (capacity() == 0))
166 return true;
167 long offset = mappingOffset();
168 long length = mappingLength(offset);
169 return isLoaded0(mappingAddress(offset), length, Bits.pageCount(length));
170 }
171
172 // not used, but a potential target for a store, see load() for details.
173 private static byte unused;
174
175 /**
176 * Loads this buffer's content into physical memory.
177 *
178 * <p> This method makes a best effort to ensure that, when it returns,
179 * this buffer's content is resident in physical memory. Invoking this
180 * method may cause some number of page faults and I/O operations to
181 * occur. </p>
182 *
183 * @return This buffer
184 */
185 public final MappedByteBuffer load() {
186 if (fd == null) {
187 return this;
188 }
189 // no need to load a persistent mapped buffer
190 if (isPersistent()) {
191 return this;
192 }
193 if ((address == 0) || (capacity() == 0))
194 return this;
195 long offset = mappingOffset();
196 long length = mappingLength(offset);
197 load0(mappingAddress(offset), length);
198
199 // Read a byte from each page to bring it into memory. A checksum
200 // is computed as we go along to prevent the compiler from otherwise
201 // considering the loop as dead code.
202 Unsafe unsafe = Unsafe.getUnsafe();
203 int ps = Bits.pageSize();
204 int count = Bits.pageCount(length);
205 long a = mappingAddress(offset);
206 byte x = 0;
207 try {
208 for (int i=0; i<count; i++) {
209 // TODO consider changing to getByteOpaque thus avoiding
210 // dead code elimination and the need to calculate a checksum
211 x ^= unsafe.getByte(a);
212 a += ps;
222
223 /**
224 * Forces any changes made to this buffer's content to be written to the
225 * storage device containing the mapped file.
226 *
227 * <p> If the file mapped into this buffer resides on a local storage
228 * device then when this method returns it is guaranteed that all changes
229 * made to the buffer since it was created, or since this method was last
230 * invoked, will have been written to that device.
231 *
232 * <p> If the file does not reside on a local device then no such guarantee
233 * is made.
234 *
235 * <p> If this buffer was not mapped in read/write mode ({@link
236 * java.nio.channels.FileChannel.MapMode#READ_WRITE}) then invoking this
237 * method has no effect. </p>
238 *
239 * @return This buffer
240 */
241 public final MappedByteBuffer force() {
242 return force(0, capacity());
243 }
244
245 /**
246 * Forces any changes made to some subregion of this buffer's
247 * content to be written to the storage device containing the
248 * mapped file.
249 *
250 * <p> If the file mapped into this buffer resides on a local storage
251 * device then when this method returns it is guaranteed that all changes
252 * made to the buffer since it was created, or since this method was last
253 * invoked, will have been written to that device.
254 *
255 * <p> If the file does not reside on a local device then no such guarantee
256 * is made.
257 *
258 * <p> If this buffer was not mapped in read/write mode ({@link
259 * java.nio.channels.FileChannel.MapMode#READ_WRITE}) then invoking this
260 * method has no effect. </p>
261 *
262 * @param from
263 * The offset to the first byte in the buffer subregion
264 * that is to be written back to storage
265 *
266 * @param to
267 * The offset to the first byte beyond the buffer subregion
268 * that is to be written back to storage
269 *
270 * @return This buffer
271 */
272 public final MappedByteBuffer force(long from, long to) {
273 if (fd == null) {
274 return this;
275 }
276 if ((address != 0) && (capacity() != 0)) {
277 // check inputs
278 if (from < 0 || from >= capacity()) {
279 throw new IllegalArgumentException();
280 }
281 if (to < from || to > capacity()) {
282 throw new IllegalArgumentException();
283 }
284
285 long offset = mappingOffset();
286 long a = mappingAddress(offset) + from;
287 long length = offset + to;
288 if (isPersistent) {
289 // simply force writeback of associated cache lines
290 Unsafe unsafe = Unsafe.getUnsafe();
291 unsafe.writebackMemory(a, length);
292 } else {
293 // writeback using device associated with fd
294 force0(fd, a, length);
295 }
296 }
297 return this;
298 }
299
300 private native boolean isLoaded0(long address, long length, int pageCount);
301 private native void load0(long address, long length);
302 private native void force0(FileDescriptor fd, long address, long length);
303
304 // -- Covariant return type overrides
305
306 /**
307 * {@inheritDoc}
308 */
309 @Override
310 public final MappedByteBuffer position(int newPosition) {
311 super.position(newPosition);
312 return this;
313 }
314
315 /**
|