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ReadFile

Semantics

The player type ReadFile corresponds to the capability of performing input from a file. It captures the semantics of a Module performing input from a file via a FileIO connection (as opposed to a Filter performing input from a file via a Pipe connection). In a UniCon architectural description, the ReadFile player is used to create an abstraction for an input operation in the underlying implementation of a system. The word operation here is not meant to refer to a specific function call or language construct, but refers to a group of language constructs or system calls that implement some capability (e.g., in C, a sequence of function calls to open, read, and close that perform some capability in the application).

Component Types In

A player of type ReadFile can legally be defined in components of the following types:

General

Module

Role Type
Associations

A player of type ReadFile can legally be associated with the following role type in a FileIO connection:

Reader (of FileIO connector)

Properties

The following properties can be legally included in the property list of a ReadFile player:

MaxAssocs

The syntax for the MaxAssocs property in a ReadFile player is a single <integer> surrounded by parentheses:

MAXASSOCS (1)

MinAssocs

The syntax for the MinAssocs property in a ReadFile player is a single <integer> surrounded by parentheses:

MINASSOCS (1)

Signature

The syntax for the Signature property in a ReadFile player is a list of items that are either <identifier>s or "string"s, surrounded by parentheses:

SIGNATURE (int)
SIGNATURE (int, "char *", double)

Implementation Considerations

In the source code implementation of a system, a player of type ReadFile is implemented as a set of language constructs or system calls that implement some input capability in the application. For example, a player of type ReadFile might consist of a set of function calls to open, read, and close that reads the data from a file into a buffer in memory:

  #include <stdio.h>
  #include <fcntl.h>

  #define MAX_BUF_LEN      256
  #define FOR_INPUT      "r"

  /* external data definitions required to support the code fragments below */

  char input_buffer[MAX_BUF_LEN + 1];
  int i, fd;

  fd = open ("datafile", O_RDONLY);
  for (i = 0; 
     i < MAX_BUF_LEN;
     i++)
    if (read (fd, &input_buffer[i], ONE_CHARACTER) == 0)
      break;
  close (fd);