If the time in the TIMEOUT parameter elapses before an event is detected, the SELECT call returns and RETCODE is set to 0.

Keyword

Description

MAXSOC

Input parameter. A fullword binary field that specifies the largest socket descriptor value being checked. The SELECT call tests only bits that are in the range 0 through the MAXSOC value minus 1. For example, if you set the MAXSOC value to 50, the range is 0 – 49.

ERRNO

Output parameter. A fullword binary field. If RETCODE is negative, ERRNO contains a valid error number. Otherwise, ignore ERRNO.

See Socket call error return codes for information about ERRNO return codes.

RETCODE

Output parameter. A fullword binary field that returns one of the following values:

Value

Description

>0

Indicates the number of ready sockets in the three return masks.

Note: If the number of ready sockets is greater than 65535, only 65535 is reported.

=0

Indicates that the SELECT time limit has expired.

-1

Check ERRNO for an error code.

TIMEOUT

Input parameter.

If TIMEOUT is not specified, the SELECT call blocks until a socket becomes ready.

If TIMEOUT is specified, TIMEOUT is the maximum interval for the SELECT call to wait until completion of the call. If you want SELECT to poll the sockets and return immediately, TIMEOUT should be specified to point to a 0-valued TIMEVAL structure.

TIMEOUT is specified in the two-word TIMEOUTas follows:

• TIMEOUT-SECONDS, word one of TIMEOUT, is the seconds component of the timeout value.
• TIMEOUT-MICROSEC, word two of TIMEOUT, is the microseconds component of the timeout value (0–999999).

For example, if you want SELECT to timeout after 3.5 seconds, set TIMEOUT-SECONDS to 3 and TIMEOUT-MICROSEC to 500000.

For APITYPE=3 with an ECB specified, the SELECT call will return immediately because it is asynchronous; the ECB will be POSTed when the timer pops.

RSNDMSK

Input parameter. The bit-mask array to control checking for read interrupts. If this parameter is not specified or the specified bit-mask is zeros, the SELECT does not check for read interrupts. The length of this bit-mask array is dependent on the value in MAXSOC and must be a multiple of 4 bytes. See Selecting requests in a concurrent server program for more information.

RRETMSK

Output parameter. The bit-mask array returned by the SELECT if RSNDMSK is specified. The length of this bit-mask array is dependent on the value in MAXSOC and must be a multiple of 4 bytes. See Selecting requests in a concurrent server program for more information.

WSNDMSK

Input parameter. The bit-mask array to control checking for write interrupts. If this parameter is not specified or the specified bit-mask is zeros, the SELECT does not check for write interrupts. The length of this bit-mask array is dependent on the value in MAXSOC and must be a multiple of 4 bytes. See Selecting requests in a concurrent server program for more information.

WRETMSK

Output parameter. The bit-mask array returned by the SELECT if WSNDMSK is specified. The length of this bit-mask array is dependent on the value in MAXSOC and must be a multiple of 4 bytes. See Selecting requests in a concurrent server program for more information.

ESNDMSK

Input parameter. The bit-mask array to control checking for exception interrupts. If this parameter is not specified or the specified bit-mask is zeros, the SELECT does not check for exception interrupts. The length of this bit-mask array is dependent on the value in MAXSOC and must be a multiple of 4 bytes. See Selecting requests in a concurrent server program for more information.

ERETMSK

Output parameter. The bit-mask array returned by the SELECT if ESNDMSK is specified. The length of this bit-mask array is dependent on the value in MAXSOC and must be a multiple of 4 bytes. See Selecting requests in a concurrent server program for more information.

ECB or REQAREA

Input parameter. This parameter is required if you are using APITYPE=3. It points to a 104-byte field containing:

For ECB

A 4-byte ECB posted by TCP/IP when the macro completes.

For REQAREA

A 4-byte user token (set by you) that is presented to your exit when the response to this function request is complete.

For ECB/REQAREA

The last 100 bytes is a storage field used by the interface to save the state information.

Note: This storage must not be modified until the macro function has completed and the ECB has been posted, or the asynchronous exit has been driven.

ERROR

Input parameter. The location in your program to receive control when the application programming interface (API) processing module cannot be loaded.

TASK

Input parameter. The location of the task storage area in your program.