Syntax:
SYNCHRONIZE(<integer value> | ALL | , | <logic expression> |
EQUFIELD(<field>) | ) <associated instruction>;
SYNCHRONIZE is used to retain messages that
come to a node, maybe at different times, and to release together
a set of them at the same time (synchronized) when certain
conditions are met.
The associated instruction must contain a SENDTO instruction to
send the synchronized set. The instruction is suited to simulate synchronization processes in assembling lines, and gathering items for batch processing.
The instruction must be used in a node with an EL that has the ability to send messages (nodes of G, L, D, and general type with EL).
When this instruction is executed the EL is scanned from the
beginning. Each message (comparing message) is compared with those
(compared messages) that follow it. The first comparing message
is the first one in the EL. The values of the fields
of the comparing message are in the field variables.
Those of the
compared message are put in the O_<variables>.
The comparison
consists in the evaluation of the <logic expression>, that may include
field variables of the comparing
messages,
O_<variables> of
the compared message and any other type of variables and
constants. If the expression is TRUE, both, the comparing and
compared messages, are candidates to be synchronized. When all
messages are compared, the second message in the EL is taken
as the new comparing message which is compared with those
that follow it. The process is repeated so that all the
possible comparisons are made. If at any point of the process a number of
candidates reach the value expressed by <integer value>, then
synchronization is successful. Then, the synchronized messages are taken
out of the list one by one and for each synchronized
message the <associated instruction> is executed.
The whole process is then repeated to see if another successful
synchronization group of the required size is possible with the
remaining messages.
If the parameter ALL is used, there is not limit for the synchronized set.
If the <logical expression> is reduced to the
constant TRUE, the messages are inconditionally synchronized
up to the specified number (or all the messages if ALL is used).
If there is not successful synchronization at all, nothing is done and
the <associated instruction> is not executed.
If the function EQUFIELD(<field>) is used instead of the
<logical condition>, messages with the
same values on that field are synchronized.
In all cases, it is assumed that all the messages in the EL have the fields that are used by the synchronizing conditions.
The <associated instruction> executed for each
successful synchronization, may have instructions to change the
fields of the messages (assigning values to field
variables) and must have a SENDTO instruction to dispose of the message
that represents them. Note that this <associated instruction>
may change the values of variables in the <logical condition>
and in the <integer value>, so changing the synchronization
conditions for the next group or for a new execution of the
SYNCHRONIZE instruction.
If there was some successful synchronization, the variable SYNC is
put to TRUE, otherwise it is put to FALSE.
See the instruction ASSEMBLE (6.1). See example 11 (GLIDER examples book).