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All computers do not store the bytes that comprise a multi-byte value in the same order. Consider a 16-bit internet that is made up of 2 bytes. Two ways to store this value −Little Endian − In this scheme, low-order byte is stored on the starting address (A) and high-order byte is stored on the next address (A + 1).Big Endian − In this scheme, high-order byte is stored on the starting address (A) and low-order byte is stored on the next address (A + 1).To allow machines with different byte order conventions communicate with each other, the Internet protocols ... Read More
Linux can manage the processes in the system, each process is represented by a task_struct C data structure. It is found in the include file in the kernel source-code directory. The task vector is an array of pointers to every task_struct data structure in the system. As well as the normal type of process, Linux supports real time processes. All the required information i.e; the state of the process, scheduling and memory-management information, list of open files, and pointers to the process’s parent and a list of its children and siblings are contained in this structure.A process who creates ... Read More
A program loaded into memory and executing is called a process. In simple, a process is a program in execution.When a program is created then it is just some pieces of Bytes which is stored in Hard Disk as a passive entity. Then the program starts loading in memory and become an active entity, when a program is double-clicked in windows or entering the name of the executable file on the command line. (i.e. a.out or prog.exe)Let’s look at each memory segment and how does a process look like within memory −Figure: Process in MemoryTEXTA process is more than the ... Read More
Deadlock can be occurred in a multithreaded Pthread program using mutex locks. Let’s see how it can be occurred. An unlocked mutex is initialized by the pthread_mutex_init() function.Using pthread_mutex_lock() and pthread_mutex_unlock() Mutex locks are acquired and released. If a thread try to acquire a locked mutex, the call to pthread_mutex_lock() blocks the thread until the owner of the mutex lock invokes pthread_mutex_unlock().Let’s take an example, two Mutex locks are created in the following Code −/* Create and initialize the mutex locks */ pthread mutex t mutex1; pthread mutex t mutex2; pthread mutex init(&mutex1, NULL); pthread mutex init(&mutex2, NULL);Next, two threads ... Read More
Transactional memory originated in database theory, provides an alternative strategy for process synchronization.A memory transaction is atomic is a sequence of memory read–write operations. The memory transaction is committed, if all operations in a transaction are completed. Otherwise, the operations must be aborted and rolled back. The ease of transactional memory can be obtained through features added to a programming language. Consider an example. Suppose we have a function update() that modifies shared data. Traditionally, this function would be written using mutex locks (or semaphores) such as the following −void update (){ acquire(); /* modify shared data */ ... Read More
Solaris implements variety of locks to support multitasking, multithreading and multiprocessing. It uses adaptive mutexes, conditional variables, semaphores, read-write locks, turnstiles to control access to critical sections.An adaptive mutex uses for protecting every critical data item which are only accessed by short code segments.On A multiprocessor system it starts as a standard semaphore spin-lock. If the lock is held by a thread which is running on another CPU then the thread spins. If the lock is held by a thread which is currently in run state, the thread blocks, going to sleep until it is awakened by the signal of ... Read More
Windows operating system is a multithreaded kernel that provide support for real time application and multiprocessors. On uniprocessor system, Windows provides interrupt masks to protect access to global resources. It protects access to global resource using spinlock. The kernel uses spinlocks only to protect short code segment like Solaris. The kernel ensures that while holding a spinlock, a thread will never be preempted.Windows provide dispatcher object for thread synchronization according to several different mechanisms including mutexes, semaphores, events and timers. The system protects shared data by requiring a thread to gain ownership of a mutex for accessing the data and ... Read More
To implement monitor using semaphores, for each monitor, a semaphore mutex (which is initialized to 1) is provided. Wait(mutex) must be executed by a process before entering the monitor and must execute signal(mutex) after leaving the monitor. Since a signaling process must wait until the resumed process either leaves or waits, an additional semaphore, next, is introduced, initialized to 0. next can be used by The signaling processes to suspend themselves. An integer variable next_count is also provided to count the number of processes suspended on next. Thus, each external function F is replaced by-wait(mutex); … body of F ... ... Read More
Grand Central Dispatch (GCD) - a technology for Apple’s Mac OS X and iOS operating systems-is a combination of extensions to the C language, an API, and a run-time library that allows application developers to identify sections of code to run in parallel. Like OpenMP, GCD manages most of the details of threading. GCD identifies extensions to the C and C++ languages known as blocks. A block is simply a self-contained unit of work. It is specified by a caret ˆ inserted in front of a pair of braces { }. A simple example of a block is shown below ... Read More
OpenMP is a set of compiler directives as well as an API for programs written in C, C++, or FORTRAN that provides support for parallel programming in shared-memory environments. OpenMP identifies parallel regions as blocks of code that may run in parallel. Application developers insert compiler directives into their code at parallel regions, and these directives instruct the OpenMP run-time library to execute the region in parallel. The following C program illustrates a compiler directive above the parallel region containing the printf() statement −#include #include int main(int argc, char *argv[]){ /* sequential code */ #pragma omp ... Read More