Foreign Function & Memory API:安全地访问 native

  1 getpid:27372(Java 里 ProcessHandle.current().pid()=27372)
  2 strlen("Hello, FFM!")=11;往返读回 Hello, FFM!;段大小 12(含结尾的 0)
  3 qsort 用 Java 比较器排序:[1, 3, 5, 7, 9]
  4 C 的 sizeof(Rec)=32,offsetof tag/id/big/d/name=0/4/8/16/24,对齐 8
    Java 的 REC.byteSize()=32,offset id/big/d/name=4/8/16/24,byteAlignment 8
  5 C 填充的结构体在 Java 里读出:tag=7,id=42,big=42000000294,d=10.5,name=rec
  6 C 的 sum_array 对 Java 分配的 int[10]:55
  7 错误:
     越界读(offset 14 读 int,段 16 字节):IndexOutOfBoundsException: Out of bound access on segment MemorySegment{ heapBase: Optional.empty address:523132688992 limit: 16 }; new offset = 14; new length = 4
     未对齐读(offset 4 读 long):IllegalArgumentException: Misaligned access at address: 523132688996
     负偏移:IndexOutOfBoundsException: Out of bound access on segment MemorySegment{ heapBase: Optional.empty address:523132688992 limit: 16 }; new offset = -4; new length = 4
     只读段写入:UnsupportedOperationException: Attempt to write a read-only segment
     Arena 关闭之后访问:IllegalStateException: Already closed
     重复关闭 Arena:IllegalStateException: Already closed
     confined Arena 的段被其它线程访问:WrongThreadException: Attempted access outside owning thread
     shared Arena 的段在其它线程写入后读到:5
     ofAuto Arena(由 GC 回收):读到 3
     ofAuto 不能手动 close:UnsupportedOperationException: Attempted to close a non-closeable session
  8 getpid 下行调用:2000 万次共 112 ms,平均 5.6 ns/次(x=true)

  编译失败: <jtmp>/j163a/Main.java:4: error: ValueLayout is a preview API and is disabled by default.
    import static java.lang.foreign.ValueLayout.*;
                                   ^
      (use --enable-preview to enable preview APIs)

  1 getpid:27378(Java 里 ProcessHandle.current().pid()=27378)
  2 strlen("Hello, FFM!")=11;往返读回 Hello, FFM!;段大小 12(含结尾的 0)
  3 qsort 用 Java 比较器排序:[1, 3, 5, 7, 9]
  4 C 的 sizeof(Rec)=32,offsetof tag/id/big/d/name=0/4/8/16/24,对齐 8
    Java 的 REC.byteSize()=32,offset id/big/d/name=4/8/16/24,byteAlignment 8
  5 C 填充的结构体在 Java 里读出:tag=7,id=42,big=42000000294,d=10.5,name=rec
  6 C 的 sum_array 对 Java 分配的 int[10]:55
  7 错误:
     越界读(offset 14 读 int,段 16 字节):IndexOutOfBoundsException: Out of bound access on segment MemorySegment{ kind: native, address: 0x77ea101260, byteSize: 16 }; attempting to access an element of length 4 at offs
     未对齐读(offset 4 读 long):IllegalArgumentException: Target offset 4 is incompatible with alignment constraint 8 (of j8) for segment MemorySegment{ kind: native, address: 0x77ea101260, byteSize: 16 }
     负偏移:IndexOutOfBoundsException: Out of bound access on segment MemorySegment{ kind: native, address: 0x77ea101260, byteSize: 16 }; attempting to access an element of length 4 at offs
     只读段写入:IllegalArgumentException: Attempt to write a read-only segment
     Arena 关闭之后访问:IllegalStateException: Already closed
     重复关闭 Arena:IllegalStateException: Already closed
     confined Arena 的段被其它线程访问:WrongThreadException: Attempted access outside owning thread
     shared Arena 的段在其它线程写入后读到:5
     ofAuto Arena(由 GC 回收):读到 3
     ofAuto 不能手动 close:UnsupportedOperationException: Attempted to close a non-closeable session
  8 getpid 下行调用:2000 万次共 147 ms,平均 7.4 ns/次(x=true)
  WARNING: A restricted method in java.lang.foreign.Linker has been called
  WARNING: java.lang.foreign.Linker::downcallHandle has been called by Main in an unnamed module (file:<jtmp>/j163a/out/)
  WARNING: Use --enable-native-access=ALL-UNNAMED to avoid a warning for callers in this module
  WARNING: Restricted methods will be blocked in a future release unless native access is enabled

  1 getpid:27382(Java 里 ProcessHandle.current().pid()=27382)
  2 strlen("Hello, FFM!")=11;往返读回 Hello, FFM!;段大小 12(含结尾的 0)
  3 qsort 用 Java 比较器排序:[1, 3, 5, 7, 9]
  4 C 的 sizeof(Rec)=32,offsetof tag/id/big/d/name=0/4/8/16/24,对齐 8
    Java 的 REC.byteSize()=32,offset id/big/d/name=4/8/16/24,byteAlignment 8
  5 C 填充的结构体在 Java 里读出:tag=7,id=42,big=42000000294,d=10.5,name=rec
  6 C 的 sum_array 对 Java 分配的 int[10]:55
  7 错误:
     越界读(offset 14 读 int,段 16 字节):IndexOutOfBoundsException: Out of bound access on segment MemorySegment{ kind: native, address: 0x7a1ee19440, byteSize: 16 }; attempting to access an element of length 4 at offs
     未对齐读(offset 4 读 long):IllegalArgumentException: Target offset 4 is incompatible with alignment constraint 8 (of j8) for segment MemorySegment{ kind: native, address: 0x7a1ee19440, byteSize: 16 }
     负偏移:IndexOutOfBoundsException: Out of bound access on segment MemorySegment{ kind: native, address: 0x7a1ee19440, byteSize: 16 }; attempting to access an element of length 4 at offs
     只读段写入:IllegalArgumentException: Attempt to write a read-only segment
     Arena 关闭之后访问:IllegalStateException: Already closed
     重复关闭 Arena:IllegalStateException: Already closed
     confined Arena 的段被其它线程访问:WrongThreadException: Attempted access outside owning thread
     shared Arena 的段在其它线程写入后读到:5
     ofAuto Arena(由 GC 回收):读到 3
     ofAuto 不能手动 close:UnsupportedOperationException: Attempted to close a non-closeable session
  8 getpid 下行调用:2000 万次共 145 ms,平均 7.3 ns/次(x=true)