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我有一个地址指向的两个进程之间的共享内存块（1024 字节）。我想将一些数据复制到这个共享内存中，并在另一个进程上读取它。来自 C 背景，似乎最容易将记录映射到该地址，然后写入记录，但它似乎没有正确复制。

目前，我正在尝试使用未经检查的转换将指针转换为指向记录的指针类型，然后复制到记录中，但是当我将原始有效负载与第二个过程中收到的有效负载进行比较时，我发现数据存在差异.

这是这样做的正确方法吗？：

type Payload_Array_Type is array (1..255) of Integer_32;

type Common_Buffer_Type is
  record
    Size : Integer_32;
    Payload : Payload_Array_Type;
  end record;

type Common_Buffer_Ptr_Type is access Common_Buffer_Type;

function Convert_Common_Memory_Ptr is new Unchecked_Conversion (
    Source => System.Address,
    Target => Common_Buffer_Ptr_Type);

Common_Memory_Ptr : System.Address;

procedure Copy_To_Common_Buffer
(
    Size : Integer_32;
    Payload : Payload_Array_Type
) is
    Common_Buffer_Ptr : Common_Buffer_Ptr_Type;
begin
    Common_Buffer_Ptr := Convert_Common_Memory_Ptr(Common_Memory_Ptr);
    Common_Buffer_Ptr.Size := Size;
    Common_Buffer_Ptr.Payload(1..255) := Payload(1..255);    
end Copy_To_Common_Buffer;
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1 回答 1

2

我会尝试这样做：

procedure Payload is 

   type Payload_Array_Type is array (1..255) of Integer_32;

   type Common_Buffer_Type is record
      Size : Integer_32;
      Payload : Payload_Array_Type;
   end record;
   for Common_Buffer_Type use record -- representation clause should be common to both processes
      Size    at 0 range 0 .. 31;
      Payload at 0 range 32 .. 1023;
   end record;
   for Common_Buffer_Type'Size use 1024; -- check this is also used in the other process.

   type Common_Buffer_Ptr_Type is access Common_Buffer_Type;

   Common_Memory_Ptr : System.Address; -- assuming this is where the shared object resides with a real address, possibly make it constant

   procedure Copy_To_Common_Buffer (Size    : in Integer_32;
                    Payload : in Payload_Array_Type) is
      Common_Buffer : Common_Buffer_Type;
      for Common_Buffer'Address use Common_Memory_Ptr; -- address overlay
   begin
      Common_Buffer := (Size => Size,
            Payload => Payload);
   end Copy_To_Common_Buffer;

begin

   Copy_To_Common_Buffer (9,(others => 876));

end Payload;

类型定义应该对两个进程是通用的，注意我使用了一个表示子句来指定组件的去向。

我使用了地址覆盖来指定我正在写作的位置，并一口气写下了整个记录。

正如@Brian Drummond 所建议的那样，还要查找 pragma volatile 的用法。

于 2015-07-18T20:36:04.197 回答