First Fit algorithm in Memory Management using Linked List
First Fit Algorithm for Memory Management: The first memory partition which is sufficient to accommodate the process is allocated.
We have already discussed first fit algorithm using arrays in this article. However, here we are going to look into another approach using a linked list where the deletion of allocated nodes is also possible.
Examples:
Input: blockSize[] = {100, 500, 200} processSize[] = {417, 112, 426, 95} Output: Block of size 426 can't be allocated Tag Block ID Size 0 1 417 1 2 112 2 0 95 After deleting block with tag id 0. Tag Block ID Size 1 2 112 2 0 95 3 1 426
Approach: The idea is to use the memory block with a unique tag id. Each process of different sizes are given block id, which signifies to which memory block they belong to, and unique tag id to delete particular process to free up space. Create a free list of given memory block sizes and allocated list of processes.
Create allocated list:
Create an allocated list of given process sizes by finding the first memory block with sufficient size to allocate memory from. If the memory block is not found, then simply print it. Otherwise, create a node and add it to the allocated linked list.
Delete process:
Each process is given a unique tag id. Delete the process node from the allocated linked list to free up some space for other processes. After deleting, use the block id of the deleted node to increase the memory block size in the free list.
Below is the implementation of the approach:
C++
// C++ implementation of the First // sit memory management algorithm // using linked list #include <bits/stdc++.h> using namespace std; // Two global counters int g = 0, k = 0; // Structure for free list struct free { int tag; int size; struct free * next; }* free_head = NULL, *prev_free = NULL; // Structure for allocated list struct alloc { int block_id; int tag; int size; struct alloc* next; }* alloc_head = NULL, *prev_alloc = NULL; // Function to create free // list with given sizes void create_free( int c) { struct free * p = ( struct free *) malloc ( sizeof ( struct free )); p->size = c; p->tag = g; p->next = NULL; if (free_head == NULL) free_head = p; else prev_free->next = p; prev_free = p; g++; } // Function to print free list which // prints free blocks of given sizes void print_free() { struct free * p = free_head; cout << "Tag\tSize\n" ; while (p != NULL) { cout << p->tag << "\t" << p->size << "\n" ; p = p->next; } } // Function to print allocated list which // prints allocated blocks and their block ids void print_alloc() { struct alloc* p = alloc_head; cout << "Tag\tBlock ID\tSize\n" ; while (p != NULL) { cout << p->tag << "\t " << p->block_id << "\t\t" << p->size << "\n" ; p = p->next; } } // Function to allocate memory to // blocks as per First fit algorithm void create_alloc( int c) { // create node for process of given size struct alloc* q = ( struct alloc*) malloc ( sizeof ( struct alloc)); q->size = c; q->tag = k; q->next = NULL; struct free * p = free_head; // Iterate to find first memory // block with appropriate size while (p != NULL) { if (q->size <= p->size) break ; p = p->next; } // Node found to allocate if (p != NULL) { // Adding node to allocated list q->block_id = p->tag; p->size -= q->size; if (alloc_head == NULL) alloc_head = q; else { prev_alloc = alloc_head; while (prev_alloc->next != NULL) prev_alloc = prev_alloc->next; prev_alloc->next = q; } k++; } else // Node found to allocate space from cout << "Block of size " << c << " can't be allocated\n" ; } // Function to delete node from // allocated list to free some space void delete_alloc( int t) { // Standard delete function // of a linked list node struct alloc *p = alloc_head, *q = NULL; // First, find the node according // to given tag id while (p != NULL) { if (p->tag == t) break ; q = p; p = p->next; } if (p == NULL) cout << "Tag ID doesn't exist\n" ; else if (p == alloc_head) alloc_head = alloc_head->next; else q->next = p->next; struct free * temp = free_head; while (temp != NULL) { if (temp->tag == p->block_id) { temp->size += p->size; break ; } temp = temp->next; } } // Driver Code int main() { int blockSize[] = { 100, 500, 200 }; int processSize[] = { 417, 112, 426, 95 }; int m = sizeof (blockSize) / sizeof (blockSize[0]); int n = sizeof (processSize) / sizeof (processSize[0]); for ( int i = 0; i < m; i++) create_free(blockSize[i]); for ( int i = 0; i < n; i++) create_alloc(processSize[i]); print_alloc(); // Block of tag id 0 deleted // to free space for block of size 426 delete_alloc(0); create_alloc(426); cout << "After deleting block" << " with tag id 0.\n" ; print_alloc(); } |
Java
// Java implementation of the First // sit memory management algorithm // using linked list public class GFG { // Two global counters static int g = 0 , k = 0 ; // Structure for free list static class free { int tag; int size; free next; } static free free_head = null ; static free prev_free = null ; // Structure for allocated list static class alloc { int block_id; int tag; int size; alloc next; } static alloc alloc_head = null ; static alloc prev_alloc = null ; // Function to create free // list with given sizes static void create_free( int c) { free p = new free(); p.size = c; p.tag = g; p.next = null ; if (free_head == null ) free_head = p; else prev_free.next = p; prev_free = p; g++; } // Function to print free list which // prints free blocks of given sizes static void print_free() { free p = free_head; System.out.println( "Tag\tSize" ); while (p != null ) { System.out.println(p.tag + "\t" + p.size); p = p.next; } } // Function to print allocated list which // prints allocated blocks and their block ids static void print_alloc() { alloc p = alloc_head; System.out.println( "Tag\tBlock ID\tSize" ); while (p != null ) { System.out.println(p.tag + "\t " + p.block_id + "\t\t" + p.size); p = p.next; } } // Function to allocate memory to // blocks as per First fit algorithm static void create_alloc( int c) { // create node for process of given size alloc q = new alloc(); q.size = c; q.tag = k; q.next = null ; free p = free_head; // Iterate to find first memory // block with appropriate size while (p != null ) { if (q.size <= p.size) break ; p = p.next; } // Node found to allocate if (p != null ) { // Adding node to allocated list q.block_id = p.tag; p.size -= q.size; if (alloc_head == null ) alloc_head = q; else { prev_alloc = alloc_head; while (prev_alloc.next != null ) prev_alloc = prev_alloc.next; prev_alloc.next = q; } k++; } else // Node found to allocate space from System.out.println( "Block of size " + c + " can't be allocated" ); } // Function to delete node from // allocated list to free some space static void delete_alloc( int t) { // Standard delete function // of a linked list node alloc p = alloc_head, q = null ; // First, find the node according // to given tag id while (p != null ) { if (p.tag == t) break ; q = p; p = p.next; } if (p == null ) System.out.println( "Tag ID doesn't exist" ); else if (p == alloc_head) alloc_head = alloc_head.next; else q.next = p.next; free temp = free_head; while (temp != null ) { if (temp.tag == p.block_id) { temp.size += p.size; break ; } temp = temp.next; } } // Driver Code public static void main(String[] args) { int blockSize[] = { 100 , 500 , 200 }; int processSize[] = { 417 , 112 , 426 , 95 }; int m = blockSize.length; int n = processSize.length; for ( int i = 0 ; i < m; i++) create_free(blockSize[i]); for ( int i = 0 ; i < n; i++) create_alloc(processSize[i]); print_alloc(); // Block of tag id 0 deleted // to free space for block of size 426 delete_alloc( 0 ); create_alloc( 426 ); System.out.println( "After deleting block" + " with tag id 0." ); print_alloc(); } } // This code is contributed by Lovely Jain |
Python3
# Python3 implementation of the First # sit memory management algorithm # using linked list # Two global counters g = 0 ; k = 0 # Structure for free list class free: def __init__( self ): self .tag = - 1 self .size = 0 self . next = None free_head = None ; prev_free = None # Structure for allocated list class alloc: def __init__( self ): self .block_id = - 1 self .tag = - 1 self .size = 0 self . next = None alloc_head = None ;prev_alloc = None # Function to create free # list with given sizes def create_free(c): global g,prev_free,free_head p = free() p.size = c p.tag = g p. next = None if free_head is None : free_head = p else : prev_free. next = p prev_free = p g + = 1 # Function to print free list which # prints free blocks of given sizes def print_free(): p = free_head print ( "Tag\tSize" ) while (p ! = None ) : print ( "{}\t{}" . format (p.tag,p.size)) p = p. next # Function to print allocated list which # prints allocated blocks and their block ids def print_alloc(): p = alloc_head print ( "Tag\tBlock ID\tSize" ) while (p is not None ) : print ( "{}\t{}\t{}\t" . format (p.tag,p.block_id,p.size)) p = p. next # Function to allocate memory to # blocks as per First fit algorithm def create_alloc(c): global k,alloc_head # create node for process of given size q = alloc() q.size = c q.tag = k q. next = None p = free_head # Iterate to find first memory # block with appropriate size while (p ! = None ) : if (q.size < = p.size): break p = p. next # Node found to allocate if (p ! = None ) : # Adding node to allocated list q.block_id = p.tag p.size - = q.size if (alloc_head = = None ): alloc_head = q else : prev_alloc = alloc_head while (prev_alloc. next ! = None ): prev_alloc = prev_alloc. next prev_alloc. next = q k + = 1 else : # Node found to allocate space from print ( "Block of size {} can't be allocated" . format (c)) # Function to delete node from # allocated list to free some space def delete_alloc(t): global alloc_head # Standard delete function # of a linked list node p = alloc_head; q = None # First, find the node according # to given tag id while (p ! = None ) : if (p.tag = = t): break q = p p = p. next if (p = = None ): print ( "Tag ID doesn't exist" ) elif (p = = alloc_head): alloc_head = alloc_head. next else : q. next = p. next temp = free_head while (temp ! = None ) : if (temp.tag = = p.block_id) : temp.size + = p.size break temp = temp. next # Driver Code if __name__ = = '__main__' : blockSize = [ 100 , 500 , 200 ] processSize = [ 417 , 112 , 426 , 95 ] m = len (blockSize) n = len (processSize) for i in range (m): create_free(blockSize[i]) for i in range (n): create_alloc(processSize[i]) print_alloc() # Block of tag id 0 deleted # to free space for block of size 426 delete_alloc( 0 ) create_alloc( 426 ) print ( "After deleting block with tag id 0." ) print_alloc() |
C#
// C# implementation of the First // sit memory management algorithm // using linked list using System; public class MainClass { // Two global counters public static int g = 0, k = 0; public class Free { // Structure for free list public int tag; public int size; public Free next; } public static Free free_head = null , prev_free = null ; // Structure for allocated list public class Alloc { public int block_id; public int tag; public int size; public Alloc next; } public static Alloc alloc_head = null , prev_alloc = null ; // Function to create free // list with given sizes public static void CreateFree( int c) { Free p = new Free(); p.size = c; p.tag = g; p.next = null ; if (free_head == null ) free_head = p; else prev_free.next = p; prev_free = p; g++; } // Function to print free list which // prints free blocks of given sizes public static void PrintFree() { Free p = free_head; Console.WriteLine( "Tag\tSize" ); while (p != null ) { Console.WriteLine(p.tag + "\t" + p.size); p = p.next; } } // Function to print allocated list which // prints allocated blocks and their block ids public static void PrintAlloc() { // create node for process of given size Alloc p = alloc_head; Console.WriteLine( "Tag\tBlock ID\tSize" ); while (p != null ) { // Iterate to find first memory // block with appropriate size Console.WriteLine(p.tag + "\t " + p.block_id + "\t\t" + p.size); p = p.next; } } public static void CreateAlloc( int c) { Alloc q = new Alloc(); q.size = c; q.tag = k; q.next = null ; Free p = free_head; while (p != null ) { if (q.size <= p.size) break ; p = p.next; } if (p != null ) { // Adding node to allocated list q.block_id = p.tag; p.size -= q.size; if (alloc_head == null ) alloc_head = q; else { prev_alloc = alloc_head; while (prev_alloc.next != null ) prev_alloc = prev_alloc.next; prev_alloc.next = q; } k++; } else // Node found to allocate space from Console.WriteLine( "Block of size " + c + " can't be allocated" ); } // Function to delete node from // allocated list to free some space public static void DeleteAlloc( int t) { // Standard delete function // of a linked list node Alloc p = alloc_head, q = null ; while (p != null ) { // First, find the node according // to given tag id if (p.tag == t) break ; q = p; p = p.next; } if (p == null ) Console.WriteLine( "Tag ID doesn't exist" ); else if (p == alloc_head) alloc_head = alloc_head.next; else q.next = p.next; Free temp = free_head; while (temp != null ) { if (temp.tag == p.block_id) { temp.size += p.size; break ; } temp = temp.next; } } // Driver Code public static void Main() { int [] blockSize = { 100, 500, 200 }; int [] processSize = { 417, 112, 426, 95 }; int m = blockSize.Length; int n = processSize.Length; for ( int i = 0; i < m; i++) CreateFree(blockSize[i]); for ( int i = 0; i < n; i++) CreateAlloc(processSize[i]); PrintAlloc(); // Block of tag id 0 deleted // to free space for block of size 426 DeleteAlloc(0); CreateAlloc(426); Console.WriteLine( "After deleting block with tag id 0." ); PrintAlloc(); } } |
Javascript
//Javascript Equivalent // Two global counters let g = 0; let k = 0 // Structure for free list class Free { constructor() { this .tag = -1; this .size = 0; this .next = null ; } } let freeHead = null ; let prevFree = null ; // Structure for allocated list class Alloc { constructor() { this .blockId = -1; this .tag = -1; this .size = 0; this .next = null ; } } let allocHead = null ; let prevAlloc = null ; // Function to create free // list with given sizes function createFree(c) { let p = new Free(); p.size = c; p.tag = g; p.next = null ; if (freeHead === null ) { freeHead = p; } else { prevFree.next = p; } prevFree = p; g+=1; } // Function to print free list which // prints free blocks of given sizes function printFree() { let p = freeHead; console.log( "Tag\tSize" ); while (p !== null ) { console.log(`${p.tag}\t${p.size}`); p = p.next; } } // Function to print allocated list which // prints allocated blocks and their block ids function printAlloc() { let p = allocHead; console.log( "Tag\tBlock ID\tSize" ); while (p !== null ) { console.log(`${p.tag}\t${p.blockId}\t${p.size}\t`); p = p.next; } } // Function to allocate memory to // blocks as per First fit algorithm function createAlloc(c) { let q = new Alloc(); q.size = c; q.tag = k; q.next = null ; let p = freeHead; // Iterate to find first memory // block with appropriate size while (p !== null ) { if (q.size <= p.size) { break ; } p = p.next; } // Node found to allocate if (p !== null ) { // Adding node to allocated list q.blockId = p.tag; p.size -= q.size; if (allocHead === null ) { allocHead = q; } else { prevAlloc = allocHead; while (prevAlloc.next !== null ) { prevAlloc = prevAlloc.next; } prevAlloc.next = q; } k+=1; } else { // Node found to allocate space from console.log(`Block of size ${c} can 't be allocated`); } } // Function to delete node from // allocated list to free some space function deleteAlloc(t) { // Standard delete function // of a linked list node let p = allocHead; let q = null; // First, find the node according // to given tag id while (p !== null) { if (p.tag === t) { break; } q = p; p = p.next; } if (p === null) { console.log("Tag ID doesn' t exist"); } else if (p === allocHead) { allocHead = allocHead.next; } else { q.next = p.next; } let temp = freeHead; while (temp !== null ) { if (temp.tag === p.blockId) { temp.size += p.size; break ; } temp = temp.next; } } // Driver Code function main() { let blockSize = [100, 500, 200]; let processSize = [417, 112, 426, 95]; let m = blockSize.length; let n = processSize.length; for (let i = 0; i < m; i++) { createFree(blockSize[i]); } for (let i = 0; i < n; i++) { createAlloc(processSize[i]); } printAlloc(); // Block of tag id 0 deleted // to free space for block of size 426 deleteAlloc(0); createAlloc(426); console.log( "After deleting block with tag id 0." ); printAlloc(); } main(); |
Block of size 426 can't be allocated Tag Block ID Size 0 1 417 1 2 112 2 0 95 After deleting block with tag id 0. Tag Block ID Size 1 2 112 2 0 95 3 1 426
Time complexity of the First Fit memory management algorithm is O(n), where n is the number of memory blocks. When a process is to be allocated, it will traverse the whole list of free blocks and check for the first block which is capable of accommodating the process. Hence, the time complexity is O(n).
Auxiliary Space complexity of the First Fit memory management algorithm is O(n), where n is the number of memory blocks. This is because the algorithm requires two linked lists for storing the free and allocated blocks. The free list stores the details of free blocks whereas the allocated list stores the details of allocated blocks. Hence, the space complexity is O(n).
Contact Us