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6.1.10 Mapping for port types

Simple ports map onto an object-like C struct with a data(), read() or write() and strerror() function members. The data() function takes no parameter and returns a pointer on the current port data. Input ports may refresh their data by invoking the read() method, while output ports may publish new data by invoking the write() method. Both read() and write() return 0 on success, or an unsigned 32bits integer representing an error code. The strerror() method can be used to transform the error code into a user readable error message.

Ports defined with the multiple flag map onto a similar struct, with the difference that data(), read() and write() methods take an additional string (const char *) parameter representing the port element name. Multiple output ports have two additional open() and close() members (also accepting a single string parameter) that dynamically create or destroy ports.

For instance, the following IDL:

      port in double in_port;
      port multiple in double multi_in_port;
      port out double out_port;
      port multiple out double multi_out_port;

would map into

      typedef struct {
         double * (*data)();
         uint32_t (*read)(void);
         const char * (*strerror)(uint32_t);
      } in_port;

      typedef struct {
         double * (*data)(const char *id);
         uint32_t (*read)(const char *id);
         const char * (*strerror)(uint32_t);
      } multi_in_port;

      typedef struct {
         double * (*data)();
         uint32_t (*write)(void);
         const char * (*strerror)(uint32_t);
      } out_port;

      typedef struct {
         double * (*data)(const char *id);
         uint32_t (*write)(const char *id);
         uint32_t (*open)(const char *id);
         uint32_t (*close)(const char *id);
         const char * (*strerror)(uint32_t);
      } multi_out_port;