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Tutorials



SEMAPHORE




Conceptually, a semaphore is a bucket. When a semaphore is allocated, a bucket that contains a fixed number of keys is created. Processes using semaphores must first procure a key from the bucket before they can continue to execute. If a specific process requires a key, only a fixed number of occurrences of that process can be in progress simultaneously. All others must wait until a sufficient number of keys is returned to the bucket. Semaphores are typically used for mutual exclusion, access control to shared resources, and basic synchronization.

Semaphore is a built-in class that provides the following methods:
-- Create a semaphore with a specified number of keys: new()
-- Obtain one or more keys from the bucket: get()
-- Return one or more keys into the bucket: put()
-- Try to obtain one or more keys without blocking: try_get()



EXAMPLE:semaphore
program main ;
semaphore sema = new(1);
initial begin
repeat(3) begin
fork
////////// PROCESS 1 ////////////////
begin
$display("1: Waiting for key");
sema.get(1);
$display("1: Got the Key");
#(10);// Do some work
sema.put(1);
$display("1: Returning back key ");
#(10);
end
////////// PROCESS 2 ////////////////
begin
$display("2: Waiting for Key");
sema.get(1);
$display("2: Got the Key");
#(10);//Do some work
sema.put(1);
$display("2: Returning back key ");
#(10);
end
join
end
#1000;
end
endprogram

RESULTS:

1: Waiting for key
1: Got the Key
2: Waiting for Key
1: Returning back key
2: Got the Key
2: Returning back key
1: Waiting for key
1: Got the Key
2: Waiting for Key
1: Returning back key
2: Got the Key
2: Returning back key
1: Waiting for key
1: Got the Key
2: Waiting for Key
1: Returning back key
2: Got the Key
2: Returning back key


Index
Introduction
Data Types
Literals
Strings
Userdefined Datatypes
Enumarations
Structures And Uniouns
Typedef
Arrays
Array Methods
Dynamic Arrays
Associative Arrays
Queues
Comparison Of Arrays
Linked List
Casting
Data Declaration
Reg And Logic
Operators 1
Operators 2
Operator Precedency
Events
Control Statements
Program Block
Procedural Blocks
Fork Join
Fork Control
Subroutines
Semaphore
Mailbox
Fine Grain Process Control

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