Kurs om
C++ Threads

Threads

What is a Thread?

• Concurrent vs. parallel
• Scheduling
• Thread types
• Synchronization
• Virtual adress space organization
• Overview of how a function-call is performed and why it’s relevant to threads
• Where do all the thread lives?

Creating Threads

• How to create a C++20 thread
• Sample hello thread
• Explicit join
• Obtaining the current thread
• Sleeping
• How to provide the thread body
• Lambda, function, functor, method pointer
• std::thread vs. std::jthread
• AutoJoiner helper class for std::thread
• Passing arguments to a thread
• The problem of mixed output and how to fix it
• Moving threads
• Swapping threads
• Thread base class
• Obtain the number of processing units
• Thread local storage

Cooperative Interruption

• How to stop a thread
• Implicit requesting stop
• Explicit requesting stop
• Register a stop call-back
• Using a stop source/token

Concurrency Problems

The Critical Section Problem

• Understanding the problem and its solution
• The ATM problem
• Account class
• ATM class
• Bank program
• Failed execution
• Critical (code) section
• What is wrong?
• Three conditions for the critical-section problem
• How to prevent the critical-section problem
• Using a mutex lock
• C++ mutex type
• Thread-safe account class
• Using a lock guard
• How to prevent self-deadlock
• Using a recursive lock
• The problem of partial mutable operations
• How to make getBalance const, but retain mutex::lock
• Using lock with time-out

The Race-Condition Problem

• Understanding the problem and its solution
• The SWIFT problem
• Moneybox class
• SWIFT class
• Sender thread
• Receiver thread
• Failed execution
• What is wrong?
• Condition synchronization
• C++ condition variables
• Thread-safe moneybox

Monitors & Capsules

• The concept monitor
• Monitor semantics
• Flexible monitor design
• Simple monitor implementation
• The concept capsule
• Simple capsule implementation

The Deadlock Problem

• The concept resource
• The Kitchen problem
• Resource class
• Cook thread
• Failed execution
• The Dining Philosophers problem
• Ed Coffmans conditions for deadlock
• How to handle deadlocks
• Fixing the Kitchen problem
• The Account Transfer problem
• C++ scoped locks
• Implementation of the Account Transfer problem

More Synchronization

Read-Write Locks

• What is a read-write lock?
• Using a std::shared_mutex
• Sample demo program

Latches & Barriers

• What is latch?
• Latch operations
• Usage of a latch
• What is barrier?
• Barrier operations
• Usage of a barrier

Semaphores

• What is a semaphore?
• Counting semaphore
• C++ semaphores
• C++ binary semaphore
• Using a semaphore as a mutex
• Implementing a queue with semaphores
• Problems with semaphores
• Semaphore can be more versatile than locks
• POSIX has two types of semaphores

Promises & Futures

• What are promises and futures?
• C++ promises and futures
• Sample usage
• Dealing with exceptions
• Asynchronous tasks
• Usage os std::async
• Execution policies
• Using s shared future
• Example; scanning the file system using async tasks

Message Queues

Implementation of a Thread-Safe Queue

• Logical design of a queue
• Handling queue capacity
• Implementation advice for an unbounded queue
• Class MessageQueueUnbounded
• Sample execution
• Implementation advice for an bounded queue
• Class MessageQueueBounded
• Sample execution using a bounded queue
• Dropping messages when queue full

Unidirectional Message Passing

• What is message-passing
• Handling pointer based messages
• Implementing interface Receivable
• Implementing a threads pipeline

Bidirectional Message Passing

• What is bidirectional message-passing?
• What is rendezvous?
• Communication patterns
• Implementation of rendezvous
• Rendezvous message class
• RPC server
• Sample client
• Execution
• Some optimizations
• Inspecting thread stack frames

Thread Pools

• What is a thread pool?
• The simplest thread pool implementation
• Tasks that return a result
• Task type
• The submit function
• The worker loop
• Pool creation and shutdown
• Sample test program

Misc. Library Parts

Parallel STL Algorithms

• What is a parallel STL algorithm
• Parallelized algorithms
• Execution policies
• Sequenced policy
• Parallel policy
• Parallel unsequenced policy
• Unsequenced policy
• Choosing a policy
• Changes to iterator requirements
• Changes in exception behaviour
• Replaced algorithms
• Do we get any speed-ups? For which work loads?
• The benchmark program

Atomic Variables

• What is an atomic type/variable?
• Using std::atomic<T>
• Operations
• The ATM problem using an atomic int

Under the Hood

POSIX Threads

• Rudimentary C API
• Creating a thread with pthread_create
• Passing arguments
• Thread configuration
• Setting the stack size
• PThread mutex
• The ATM problem as a C program, with pthreads
• PThread Condition
• PThread Read-Write locks
• PThread Barriers

Implementation of C++ Threads

• Wrapping pthreads
• Simple thread class
• Usage of the class
• Passing arguments
• Class ThreadArgs
• Usage of the modified class
• Class Mutex
• Usage of the mutex class
• Class Condition
• Usage of the condition class

Memory Management

User-Defined Memory Allocation

• Limitations of using system heap for messages
• Allocation functions of the system heap
• How the system heap is implemented
• Why the heap is a large critical section
• Heap arenas in GNU glibc; multiple locks
• What is a private heap?
• Choosing storage for messages
• Possible implementation of a consumer's private heap
• Allocation strategies
• Allocation-only storage
• Monotonic allocation
• Circular allocation
• Block-pool storage

Understanding std::pmr

• What is a polymorphic memory resource?
• Class & function overview
• Provided memory resources
• Special-form allocators
• Usage of a monotonic_buffer_resource
• STL container support for std::pmr
• Usage of unsynchronized_pool_resource

Thread Private Heaps

• Basic principle for a private heap
• Sample implementation of a std::pmr based private heap
• How to organize heap storage for messages
• Sample implementation of a std::pmr based message heap

Shared Memory

POSIX Processes

• What is a process?
• Understanding the system call fork
• Using exit and wait
• Understanding the system call exec
• Loading new program code

POSIX Shared Memory

• What is shared memory, really?
• How is it working
• Shared memory C API
• Using mmap to create memory segments
• Class SharedMemory
• Usage of the class
• Understanding the placement variant of operator new
• How to configure POSIX mutex and condition to work in shared memory
• Sample program; Producer-Consumer via shared memory

Processes with Threads & Shared Memory

• How to combine everything we discussed in this course
• Overview of the demo application
• The app part
• The Loader thread
• The Transformer thread
• The Consumer thread
• The Shared-Memory class
• The user-defined shared-memory enabled Mutex and Condition classes
• The Message-Queue class
• The Message class
• The FileSlurper class

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