selectecb

selectecb

Determines the Number of Ready Sockets

Portability: SAS/C extension

SYNOPSIS
DESCRIPTION
CAUTION

SYNOPSIS

#include <sys/types.h>
#include <sys/socket.h>
#include <lcsignal.h>

int selectecb(int nfds, fd_set *readfds, fd_set *writefds,
              fd_set *exceptfds, const struct timeval *timeout,
              struct _ecblist *ecblist, size_t ecblcnt)

DESCRIPTION

selectecb is identical to select with the exception that, in addition to returning when the timeout expires or when activity occurs on one of the specified sockets, selectecb also returns if one of the specified ECBs (Event Control Blocks) is posted.

The ecblist argument is the address of an array of structures, each of which represents one or more contiguous ECBs. Each structure contains two members, a count of the number of ECBs, and the address of an array of ECBs. The count may be 0 , in which case the ECB array address is ignored.

The declaration for the _ecblist structure is as follows:

struct _ecblist {
   size_t count;
   unsigned *ecbarr;
}

The ECB list is passed via the struct _ecblist for several reasons. It allows a static ECB list to be used in many cases, since individual ECBs can easily be removed by setting their count member to 0 . For applications that have a large number of ECBs, _ecblist facilitates organizing them into arrays; this may slightly improve the performance of selectecb , since fewer memory accesses are required to determine the addresses of all the ECBs.

Note that an ECB may be POSTed at any time. Thus, you cannot assume that no ECBs have been POSTed when selectecb returns with one or more socket descriptor bits set. An ECB may have been POSTed between the time that selectecb was returning and the time that your program checked the return code from selectecb .

If ecblist is NULL , or ecblcnt is 0 , or the count field of all the _ecblist structures is set to 0 , ECB waiting is not used and the effect is exactly the same as if select had been called.

CAUTION

The actual timing is not likely to be accurate to the microsecond. Calls to selectecb may leave asynchronous signals blocked for long periods of time.

For non-integrated sockets, the SAS/C Library blocks all asynchronous signals during routines that call the TCP/IP communications software.

For integrated sockets, selectecb may be interrupted by any unblocked signal, either managed by USS or SAS/C, in which case selectecb will return -1 , and errno will be set to EINTR . However, execution of selectecb is not interrupted by an USS signal unless the signal terminates the process.

It is a good programming practice to always check the return code for values greater than zero before testing the descriptor sets.

Chapter Contents
Previous
Next
Top of Page