Programming Language ConceptsMemory management in different

languages

Janyl Jumadinova13 April, 2017

C

I Memory management is typically manual:– the standard library functions for memory management in C,malloc and free, have become almost synonymous with manualmemory management.

I Use external software, such as the Boehm-Demers-Weisercollector (a.k.a. Boehm GC), to do garbage collection inC/C++:– use Boehm instead of traditional malloc and free in C

http://hboehm.info/gc/

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C

I Memory management is typically manual:– the standard library functions for memory management in C,malloc and free, have become almost synonymous with manualmemory management.

I Use external software, such as the Boehm-Demers-Weisercollector (a.k.a. Boehm GC), to do garbage collection inC/C++:– use Boehm instead of traditional malloc and free in C

http://hboehm.info/gc/

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C++

I The standard library functions for memory management in C++are new and delete.

I The higher abstraction level of C++ makes the bookkeepingrequired for manual memory management even harder than C.

I In addition to Boehm, we can use smart pointers as a memorymanagement solution.

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C++

I The standard library functions for memory management in C++are new and delete.

I The higher abstraction level of C++ makes the bookkeepingrequired for manual memory management even harder than C.

I In addition to Boehm, we can use smart pointers as a memorymanagement solution.

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C++

Raw pointer:

MyClass *ptr = new MyClass();

ptr->doSomething();

delete ptr; // destroy the object.

Smart pointer:

// declare a smart pointer on stack

// and pass it the raw pointer

SomeSmartPtr<MyObject> ptr(new MyObject());

ptr->DoSomething(); // use the object in some way

// destruction of the object happens automatically

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C++

Raw pointer:

MyClass *ptr = new MyClass();

ptr->doSomething();

delete ptr; // destroy the object.

Smart pointer:

// declare a smart pointer on stack

// and pass it the raw pointer

SomeSmartPtr<MyObject> ptr(new MyObject());

ptr->DoSomething(); // use the object in some way

// destruction of the object happens automatically

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Java

I Java is garbage-collected.

I Early JVMs had simple collectors that didn’t scale well for largeprograms.

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Java

Common Heap Related Switches

I -Xms: Sets the initial heap size for when the JVM starts.

I -Xmx: Sets the maximum heap size.

I -Xmn: Sets the size of the Young Generation.

I -XX:PermSize: Sets the starting size of the PermanentGeneration.

I -XX:MaxPermSize: Sets the maximum size of the PermanentGeneration.

java -Xmx12m -Xms3m -XX:+UseG1GC -jar

c:..Java2demo.jar

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Java

I Serial GC: both minor and major garbage collections are doneserially

I Parallel GC: uses multiple threads to perform the younggeneration garbage collection

I Concurrent Mark Sweep (CMS): collects the tenuredgeneration, does most of the garbage collection workconcurrently with the application threads

I G1 Garbage Collector: available in Java 7 and is designed tobe the long term replacement for the CMS collector; parallel,concurrent, and incrementally compacting.

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C#

I C# runs on the Common Language Runtime, the virtualmachine from the .NET Framework.

I It also runs on the open source Mono compiler (go-mono.comand gotmono.com).

I Memory is automatically managed– memory is allocated when an object is created, and reclaimedat some point after the object becomes unreachable.

I The Mono runtime comes with two collectors: theBoehm-Demers-Weiser conservative collector and a generationalcopying collector.

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C#

I C# runs on the Common Language Runtime, the virtualmachine from the .NET Framework.

I It also runs on the open source Mono compiler (go-mono.comand gotmono.com).

I Memory is automatically managed– memory is allocated when an object is created, and reclaimedat some point after the object becomes unreachable.

I The Mono runtime comes with two collectors: theBoehm-Demers-Weiser conservative collector and a generationalcopying collector.

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C#

I C# runs on the Common Language Runtime, the virtualmachine from the .NET Framework.

I It also runs on the open source Mono compiler (go-mono.comand gotmono.com).

I Memory is automatically managed– memory is allocated when an object is created, and reclaimedat some point after the object becomes unreachable.

I The Mono runtime comes with two collectors: theBoehm-Demers-Weiser conservative collector and a generationalcopying collector.

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C#

I C# supports finalization (classes may have destructorfunctions, which are run just before the object is reclaimed bythe memory manager), and weak references (via theWeakReference class).

I In OOP, a finalizer is a special method that performs some formof cleanup:– it is executed during object destruction, prior to the objectbeing deallocated

I Weak reference is does not protect the referenced object fromcollection by the GC.

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C#

I C# supports finalization (classes may have destructorfunctions, which are run just before the object is reclaimed bythe memory manager), and weak references (via theWeakReference class).

I In OOP, a finalizer is a special method that performs some formof cleanup:– it is executed during object destruction, prior to the objectbeing deallocated

I Weak reference is does not protect the referenced object fromcollection by the GC.

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C#

I C# supports finalization (classes may have destructorfunctions, which are run just before the object is reclaimed bythe memory manager), and weak references (via theWeakReference class).

I In OOP, a finalizer is a special method that performs some formof cleanup:– it is executed during object destruction, prior to the objectbeing deallocated

I Weak reference is does not protect the referenced object fromcollection by the GC.

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Python

I There are several implementations running on a variety ofvirtual machines:– the original CPython implementation runs on its own virtualmachine– IronPython runs on the Common Language Runtime– Jython on the Java Virtual Machine

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Python

I CPython manages memory using a mixture of referencecounting and non-moving mark-and-sweep garbage collection.

I Reference counting ensures prompt deletion of objects whentheir reference count falls to zero, while the garbage collectorreclaims cyclic data structures.

I The language supports finalization (classes may have a del

method, which is run just before the object is destroyed), andweak references (via the weakref module).

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Reference Counting GC Method

I Every value has associated with it a count of how manyreferences it has.

I It is incremented each time a reference to the object is shared.

I It is decremented whenever a pointer to the object disappears.

I When the count reaches zero, the value’s space can safely berestored for future reuse (garbage collected).

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JavaScript

I JavaScript is a scripting language used by web browsers.

I Despite the C++-like syntax (with new and delete

operators), JavaScript is garbage-collected.

I Mark and Sweep algorithm is used for GC.

I Memory Leaks (accidental global variables, forgotten callbacks,closures)

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JavaScript

I JavaScript is a scripting language used by web browsers.

I Despite the C++-like syntax (with new and delete

operators), JavaScript is garbage-collected.

I Mark and Sweep algorithm is used for GC.

I Memory Leaks (accidental global variables, forgotten callbacks,closures)

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Lisp

I Lisp was invented by John McCarthy around 1958 for themanipulation of symbolic expressions.

I As part of the original implementation of Lisp, he inventedgarbage collection.

“This process, because it is entirely automatic, ismore convenient for the programmer than a system inwhich he has to keep track of lists and erase unwantedlists.” McCarthy

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Lisp

I Lisp was invented by John McCarthy around 1958 for themanipulation of symbolic expressions.

I As part of the original implementation of Lisp, he inventedgarbage collection.

“This process, because it is entirely automatic, ismore convenient for the programmer than a system inwhich he has to keep track of lists and erase unwantedlists.” McCarthy

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PostScript

I The PostScript language is an interpretive language withpowerful graphics features, widely used as a page descriptionlanguage for printers and typesetters.

I Level 1 PostScript language has a simple stack-like memorymanagement model, using save and restore operators torecycle memory.

I In addition, Level 2 and 3 PostScript language also usesautomatic garbage collection.

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PostScript

I The PostScript language is an interpretive language withpowerful graphics features, widely used as a page descriptionlanguage for printers and typesetters.

I Level 1 PostScript language has a simple stack-like memorymanagement model, using save and restore operators torecycle memory.

I In addition, Level 2 and 3 PostScript language also usesautomatic garbage collection.

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PostScript

I The PostScript language is an interpretive language withpowerful graphics features, widely used as a page descriptionlanguage for printers and typesetters.

I Level 1 PostScript language has a simple stack-like memorymanagement model, using save and restore operators torecycle memory.

I In addition, Level 2 and 3 PostScript language also usesautomatic garbage collection.

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Prolog

I A logic programming language invented by Alain Colmeraueraround 1970, Prolog is popular in the AI and symboliccomputation community.

I It deals directly with relationships and inference rather thanfunctions or commands.

I Storage is automatically managed using a garbage collector.

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Prolog

I A logic programming language invented by Alain Colmeraueraround 1970, Prolog is popular in the AI and symboliccomputation community.

I It deals directly with relationships and inference rather thanfunctions or commands.

I Storage is automatically managed using a garbage collector.

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