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What is a semaphore? How do they work? (Example in C)

Semaphore Class (System.Threading) | Microsoft Docs

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Summary of article content: Articles about Semaphore Class (System.Threading) | Microsoft Docs The main thread uses the Release(Int32) method overload to increase the semaphore count to its maximum, allowing three threads to enter the semaphore. Each … …
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Table of Contents:

Definition

Examples

Remarks

Constructors

Fields

Properties

Methods

Explicit Interface Implementations

Extension Methods

Applies to

Thread Safety

Semaphore Class (System.Threading)

Table of contents

Semaphore Class

Reference

Definition

Important Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Limits the number of threads that can access a resource or pool of resources concurrently.

In this article

public ref class Semaphore sealed : System::Threading::WaitHandle

public sealed class Semaphore : System.Threading.WaitHandle
[System.Runtime.InteropServices.ComVisible(false)] public sealed class Semaphore : System.Threading.WaitHandle

type Semaphore = class inherit WaitHandle
[] type Semaphore = class inherit WaitHandle

Public NotInheritable Class Semaphore Inherits WaitHandle

Inheritance Object WaitHandle Semaphore

Inheritance Object MarshalByRefObject WaitHandle Semaphore

Attributes ComVisibleAttribute

Examples

The following code example creates a semaphore with a maximum count of three and an initial count of zero. The example starts five threads, which block waiting for the semaphore. The main thread uses the Release(Int32) method overload to increase the semaphore count to its maximum, allowing three threads to enter the semaphore. Each thread uses the Thread.Sleep method to wait for one second, to simulate work, and then calls the Release() method overload to release the semaphore. Each time the semaphore is released, the previous semaphore count is displayed. Console messages track semaphore use. The simulated work interval is increased slightly for each thread, to make the output easier to read.

#using using namespace System; using namespace System::Threading; public ref class Example { private: // A semaphore that simulates a limited resource pool. // static Semaphore^ _pool; // A padding interval to make the output more orderly. static int _padding; public: static void Main() { // Create a semaphore that can satisfy up to three // concurrent requests. Use an initial count of zero, // so that the entire semaphore count is initially // owned by the main program thread. // _pool = gcnew Semaphore( 0,3 ); // Create and start five numbered threads. // for ( int i = 1; i <= 5; i++ ) { Thread^ t = gcnew Thread( gcnew ParameterizedThreadStart( Worker ) ); // Start the thread, passing the number. // t->Start( i ); } // Wait for half a second, to allow all the // threads to start and to block on the semaphore. // Thread::Sleep( 500 ); // The main thread starts out holding the entire // semaphore count. Calling Release(3) brings the // semaphore count back to its maximum value, and // allows the waiting threads to enter the semaphore, // up to three at a time. // Console::WriteLine( L”Main thread calls Release(3).” ); _pool->Release( 3 ); Console::WriteLine( L”Main thread exits.” ); } private: static void Worker( Object^ num ) { // Each worker thread begins by requesting the // semaphore. Console::WriteLine( L”Thread {0} begins and waits for the semaphore.”, num ); _pool->WaitOne(); // A padding interval to make the output more orderly. int padding = Interlocked::Add( _padding, 100 ); Console::WriteLine( L”Thread {0} enters the semaphore.”, num ); // The thread’s “work” consists of sleeping for // about a second. Each thread “works” a little // longer, just to make the output more orderly. // Thread::Sleep( 1000 + padding ); Console::WriteLine( L”Thread {0} releases the semaphore.”, num ); Console::WriteLine( L”Thread {0} previous semaphore count: {1}”, num, _pool->Release() ); } };

using System; using System.Threading; public class Example { // A semaphore that simulates a limited resource pool. // private static Semaphore _pool; // A padding interval to make the output more orderly. private static int _padding; public static void Main() { // Create a semaphore that can satisfy up to three // concurrent requests. Use an initial count of zero, // so that the entire semaphore count is initially // owned by the main program thread. // _pool = new Semaphore(0, 3); // Create and start five numbered threads. // for(int i = 1; i <= 5; i++) { Thread t = new Thread(new ParameterizedThreadStart(Worker)); // Start the thread, passing the number. // t.Start(i); } // Wait for half a second, to allow all the // threads to start and to block on the semaphore. // Thread.Sleep(500); // The main thread starts out holding the entire // semaphore count. Calling Release(3) brings the // semaphore count back to its maximum value, and // allows the waiting threads to enter the semaphore, // up to three at a time. // Console.WriteLine("Main thread calls Release(3)."); _pool.Release(3); Console.WriteLine("Main thread exits."); } private static void Worker(object num) { // Each worker thread begins by requesting the // semaphore. Console.WriteLine("Thread {0} begins " + "and waits for the semaphore.", num); _pool.WaitOne(); // A padding interval to make the output more orderly. int padding = Interlocked.Add(ref _padding, 100); Console.WriteLine("Thread {0} enters the semaphore.", num); // The thread's "work" consists of sleeping for // about a second. Each thread "works" a little // longer, just to make the output more orderly. // Thread.Sleep(1000 + padding); Console.WriteLine("Thread {0} releases the semaphore.", num); Console.WriteLine("Thread {0} previous semaphore count: {1}", num, _pool.Release()); } } Imports System.Threading Public Class Example ' A semaphore that simulates a limited resource pool. ' Private Shared _pool As Semaphore ' A padding interval to make the output more orderly. Private Shared _padding As Integer _ Public Shared Sub Main() ‘ Create a semaphore that can satisfy up to three ‘ concurrent requests. Use an initial count of zero, ‘ so that the entire semaphore count is initially ‘ owned by the main program thread. ‘ _pool = New Semaphore(0, 3) ‘ Create and start five numbered threads. ‘ For i As Integer = 1 To 5 Dim t As New Thread(New ParameterizedThreadStart(AddressOf Worker)) ‘Dim t As New Thread(AddressOf Worker) ‘ Start the thread, passing the number. ‘ t.Start(i) Next i ‘ Wait for half a second, to allow all the ‘ threads to start and to block on the semaphore. ‘ Thread.Sleep(500) ‘ The main thread starts out holding the entire ‘ semaphore count. Calling Release(3) brings the ‘ semaphore count back to its maximum value, and ‘ allows the waiting threads to enter the semaphore, ‘ up to three at a time. ‘ Console.WriteLine(“Main thread calls Release(3).”) _pool.Release(3) Console.WriteLine(“Main thread exits.”) End Sub Private Shared Sub Worker(ByVal num As Object) ‘ Each worker thread begins by requesting the ‘ semaphore. Console.WriteLine(“Thread {0} begins ” _ & “and waits for the semaphore.”, num) _pool.WaitOne() ‘ A padding interval to make the output more orderly. Dim padding As Integer = Interlocked.Add(_padding, 100) Console.WriteLine(“Thread {0} enters the semaphore.”, num) ‘ The thread’s “work” consists of sleeping for ‘ about a second. Each thread “works” a little ‘ longer, just to make the output more orderly. ‘ Thread.Sleep(1000 + padding) Console.WriteLine(“Thread {0} releases the semaphore.”, num) Console.WriteLine(“Thread {0} previous semaphore count: {1}”, _ num, _ _pool.Release()) End Sub End Class

Remarks

Use the Semaphore class to control access to a pool of resources. Threads enter the semaphore by calling the WaitOne method, which is inherited from the WaitHandle class, and release the semaphore by calling the Release method.

The count on a semaphore is decremented each time a thread enters the semaphore, and incremented when a thread releases the semaphore. When the count is zero, subsequent requests block until other threads release the semaphore. When all threads have released the semaphore, the count is at the maximum value specified when the semaphore was created.

There is no guaranteed order, such as FIFO or LIFO, in which blocked threads enter the semaphore.

A thread can enter the semaphore multiple times, by calling the WaitOne method repeatedly. To release some or all of these entries, the thread can call the parameterless Release() method overload multiple times, or it can call the Release(Int32) method overload that specifies the number of entries to be released.

The Semaphore class does not enforce thread identity on calls to WaitOne or Release. It is the programmer’s responsibility to ensure that threads do not release the semaphore too many times. For example, suppose a semaphore has a maximum count of two, and that thread A and thread B both enter the semaphore. If a programming error in thread B causes it to call Release twice, both calls succeed. The count on the semaphore is full, and when thread A eventually calls Release, a SemaphoreFullException is thrown.

Semaphores are of two types: local semaphores and named system semaphores. If you create a Semaphore object using a constructor that accepts a name, it is associated with an operating-system semaphore of that name. Named system semaphores are visible throughout the operating system, and can be used to synchronize the activities of processes. You can create multiple Semaphore objects that represent the same named system semaphore, and you can use the OpenExisting method to open an existing named system semaphore.

A local semaphore exists only within your process. It can be used by any thread in your process that has a reference to the local Semaphore object. Each Semaphore object is a separate local semaphore.

Constructors

Semaphore(Int32, Int32) Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries. Semaphore(Int32, Int32, String) Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries, and optionally specifying the name of a system semaphore object. Semaphore(Int32, Int32, String, Boolean) Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries, optionally specifying the name of a system semaphore object, and specifying a variable that receives a value indicating whether a new system semaphore was created. Semaphore(Int32, Int32, String, Boolean, SemaphoreSecurity) Initializes a new instance of the Semaphore class, specifying the initial number of entries and the maximum number of concurrent entries, optionally specifying the name of a system semaphore object, specifying a variable that receives a value indicating whether a new system semaphore was created, and specifying security access control for the system semaphore.

Fields

WaitTimeout Indicates that a WaitAny(WaitHandle[], Int32, Boolean) operation timed out before any of the wait handles were signaled. This field is constant. (Inherited from WaitHandle)

Properties

Handle Obsolete. Obsolete. Gets or sets the native operating system handle. (Inherited from WaitHandle) SafeWaitHandle Gets or sets the native operating system handle. (Inherited from WaitHandle)

Methods

Explicit Interface Implementations

IDisposable.Dispose() This API supports the product infrastructure and is not intended to be used directly from your code. Releases all resources used by the WaitHandle. (Inherited from WaitHandle)

Extension Methods

GetAccessControl(Semaphore) Returns the security descriptors for the specified semaphore . SetAccessControl(Semaphore, SemaphoreSecurity) Sets the security descriptors for the specified semaphore. GetSafeWaitHandle(WaitHandle) Gets the safe handle for a native operating system wait handle. SetSafeWaitHandle(WaitHandle, SafeWaitHandle) Sets a safe handle for a native operating system wait handle.

Applies to

Thread Safety

This type is thread safe.

See also

What is a semaphore?

There are two essential concepts to building concurrent programs – synchronization and mutual exclusion. We will see how these two types of locks (semaphores are more generally a kind of locking mechanism) help us achieve synchronization and mutual exclusion.

A semaphore is a programming construct that helps us achieve concurrency, by implementing both synchronization and mutual exclusion. Semaphores are of two types, Binary and Counting.

A semaphore has two parts : a counter, and a list of tasks waiting to access a particular resource. A semaphore performs two operations : wait (P) [this is like acquiring a lock], and release (V)[ similar to releasing a lock] – these are the only two operations that one can perform on a semaphore. In a binary semaphore, the counter logically goes between 0 and 1. You can think of it as being similar to a lock with two values : open/closed. A counting semaphore has multiple values for count.

What is important to understand is that the semaphore counter keeps track of the number of tasks that do not have to block, i.e., they can make progress. Tasks block, and add themselves to the semaphore’s list only when the counter is zero. Therefore, a task gets added to the list in the P() routine if it cannot progress, and “freed” using the V() routine.

Now, it is fairly obvious to see how binary semaphores can be used to solve synchronization and mutual exclusion – they are essentially locks.

ex. Synchronization:

thread A{ semaphore &s; //locks/semaphores are passed by reference! think about why this is so. A(semaphore &s): s(s){} //constructor foo(){ … s.P(); ;// some block of code B2 … } //thread B{ semaphore &s; B(semaphore &s): s(s){} //constructor foo(){ … … // some block of code B1 s.V(); .. } main(){ semaphore s(0); // we start the semaphore at 0 (closed) A a(s); B b(s); }

In the above example, B2 can only execute after B1 has finished execution. Let’s say thread A comes executes first – gets to sem.P(), and waits, since the counter is 0 (closed). Thread B comes along, finishes B1, and then frees thread A – which then completes B2. So we achieve synchronization.

Now let’s look at mutual exclusion with a binary semaphore:

thread mutual_ex{ semaphore &s; mutual_ex(semaphore &s): s(s){} //constructor foo(){ … s.P(); //critical section s.V(); … … s.P(); //critical section s.V(); … } main(){ semaphore s(1); mutual_ex m1(s); mutual_ex m2(s); }

The mutual exclusion is quite simple as well – m1 and m2 cannot enter the critical section at the same time. So each thread is using the same semaphore to provide mutual exclusion for its two critical sections. Now, is it possible to have greater concurrency? Depends on the critical sections. (Think about how else one could use semaphores to achieve mutual exclusion.. hint hint : do i necessarily only need to use one semaphore?)

Counting semaphore: A semaphore with more than one value. Let’s look at what this is implying – a lock with more than one value?? So open, closed, and …hmm. Of what use is a multi-stage-lock in mutual exclusion or synchronization?

Let’s take the easier of the two:

Synchronization using a counting semaphore: Let’s say you have 3 tasks – #1 and 2 you want executed after 3. How would you design your synchronization?

thread t1{ … s.P(); //block of code B1 thread t2{ … s.P(); //block of code B2 thread t3{ … //block of code B3 s.V(); s.V(); }

So if your semaphore starts off closed, you ensure that t1 and t2 block, get added to the semaphore’s list. Then along comes all important t3, finishes its business and frees t1 and t2. What order are they freed in? Depends on the implementation of the semaphore’s list. Could be FIFO, could be based some particular priority,etc. (Note : think about how you would arrange your P’s and V;s if you wanted t1 and t2 to be executed in some particular order, and if you weren’t aware of the implementation of the semaphore)

(Find out : What happens if the number of V’s is greater than the number of P’s?)

Mutual Exclusion Using counting semaphores: I’d like you to construct your own pseudocode for this (makes you understand things better!) – but the fundamental concept is this : a counting semaphore of counter = N allows N tasks to enter the critical section freely. What this means is you have N tasks (or threads, if you like) enter the critical section, but the N+1th task gets blocked (goes on our favorite blocked-task list), and only is let through when somebody V’s the semaphore at least once. So the semaphore counter, instead of swinging between 0 and 1, now goes between 0 and N, allowing N tasks to freely enter and exit, blocking nobody!

Now gosh, why would you need such a stupid thing? Isn’t the whole point of mutual exclusion to not let more than one guy access a resource?? (Hint Hint…You don’t always only have one drive in your computer, do you…?)

To think about : Is mutual exclusion achieved by having a counting semaphore alone? What if you have 10 instances of a resource, and 10 threads come in (through the counting semaphore) and try to use the first instance?

Semaphores (Multithreaded Programming Guide)

Multithreaded Programming Guide

Semaphores

Semaphores are a programming construct designed by E. W. Dijkstra in the late 1960s. Dijkstra’s model was the operation of railroads: consider a stretch of railroad in which there is a single track over which only one train at a time is allowed.

Guarding this track is a semaphore. A train must wait before entering the single track until the semaphore is in a state that permits travel. When the train enters the track, the semaphore changes state to prevent other trains from entering the track. A train that is leaving this section of track must again change the state of the semaphore to allow another train to enter.

In the computer version, a semaphore appears to be a simple integer. A thread waits for permission to proceed and then signals that it has proceeded by performing a P operation on the semaphore.

The semantics of the operation are such that the thread must wait until the semaphore’s value is positive, then change the semaphore’s value by subtracting one from it. When it is finished, the thread performs a V operation, which changes the semaphore’s value by adding one to it. It is crucial that these operations take place atomically—they cannot be subdivided into pieces between which other actions on the semaphore can take place. In the P operation, the semaphore’s value must be positive just before it is decremented (resulting in a value that is guaranteed to be nonnegative and one less than what it was before it was decremented).

In both P and V operations, the arithmetic must take place without interference. If two V operations are performed simultaneously on the same semaphore, the net effect should be that the semaphore’s new value is two greater than it was.

The mnemonic significance of P and V is unclear to most of the world, as Dijkstra is Dutch. However, in the interest of true scholarship: P stands for prolagen, a made-up word derived from proberen te verlagen, which means try to decrease. V stands for verhogen, which means increase. This is discussed in one of Dijkstra’s technical notes, EWD 74.

sem_wait (3RT) and sem_post (3RT) correspond to Dijkstra’s P and V operations. sem_trywait (3RT) is a conditional form of the P operation: if the calling thread cannot decrement the value of the semaphore without waiting, the call returns immediately with a nonzero value.

There are two basic sorts of semaphores: binary semaphores, which never take on values other than zero or one, and counting semaphores, which can take on arbitrary nonnegative values. A binary semaphore is logically just like a mutex.

However, although it is not enforced, mutexes should be unlocked only by the thread holding the lock. There is no notion of “the thread holding the semaphore,” so any thread can perform a V (or sem_post(3RT)) operation.

Counting semaphores are about as powerful as conditional variables (used in conjunction with mutexes). In many cases, the code might be simpler when it is implemented with counting semaphores rather than with condition variables (as shown in the next few examples).

However, when a mutex is used with condition variables, there is an implied bracketing—it is clear which part of the program is being protected. This is not necessarily the case for a semaphore, which might be called the go to of concurrent programming—it is powerful but too easy to use in an unstructured, indeterminate way.

Counting Semaphores

Conceptually, a semaphore is a nonnegative integer count. Semaphores are typically used to coordinate access to resources, with the semaphore count initialized to the number of free resources. Threads then atomically increment the count when resources are added and atomically decrement the count when resources are removed.

When the semaphore count becomes zero, indicating that no more resources are present, threads trying to decrement the semaphore block wait until the count becomes greater than zero.

Operation Destination Discussion Initialize a semaphore sem_init(3RT) Increment a semaphore sem_post(3RT) Block on a semaphore count sem_wait(3RT) Decrement a semaphore count sem_trywait(3RT) Destroy the semaphore state sem_destroy(3RT)

Table 4–7 Routines for Semaphores

Because semaphores need not be acquired and released by the same thread, they can be used for asynchronous event notification (such as in signal handlers). And, because semaphores contain state, they can be used asynchronously without acquiring a mutex lock as is required by condition variables. However, semaphores are not as efficient as mutex locks.

By default, there is no defined order of unblocking if multiple threads are waiting for a semaphore.

Semaphores must be initialized before use, but they do not have attributes.

Initialize a Semaphore

sem_init(3RT)

Prototype: int sem_init(sem_t * sem , int pshared , unsigned int value );

#include sem_t sem ; int pshared ; int ret ; int value ; /* initialize a private semaphore */ pshared = 0; value = 1; ret = sem_init(& sem , pshared , value );

Use sema_init(3THR) to initialize the semaphore variable pointed to by sem to value amount. If the value of pshared is zero, then the semaphore cannot be shared between processes. If the value of pshared is nonzero, then the semaphore can be shared between processes. (For Solaris threads, see sema_init(3THR).)

Multiple threads must not initialize the same semaphore.

A semaphore must not be reinitialized while other threads might be using it.

Return Values

sem_init() returns zero after completing successfully. Any other return value indicates that an error occurred. When any of the following conditions occurs, the function fails and returns the corresponding value.

EINVAL The value argument exceeds SEM_VALUE_MAX .

ENOSPC A resource required to initialize the semaphore has been exhausted. The limit on semaphores SEM_NSEMS_MAX has been reached.

EPERM The process lacks the appropriate privileges to initialize the semaphore.

Initializing Semaphores With Intraprocess Scope

When pshared is 0, the semaphore can be used by all the threads in this process only.

#include sem_t sem ; int ret ; int count = 4; /* to be used within this process only */ ret = sem_init(& sem , 0, count);

Initializing Semaphores With Interprocess Scope

When pshared is nonzero, the semaphore can be shared by other processes.

#include sem_t sem ; int ret ; int count = 4; /* to be shared among processes */ ret = sem_init(& sem , 1, count);

Named Semaphores

The functions sem_open(3RT) , sem_getvalue(3RT) , sem_close(3RT) , and sem_unlink(3RT) are available to open , retrieve , close , and remove named semaphores. Using sem_open() , you can create a semaphore that has a name defined in the file system name space.

Named semaphores are like process shared semaphores, except that they are referenced with a pathname rather than a pshared value.

For more information about named semaphores, see sem_open(3RT) , sem_getvalue(3RT) , sem_close(3RT) , and sem_unlink(3RT) .

Increment a Semaphore

sem_post(3RT)

Prototype: int sem_post(sem_t * sem );

#include sem_t sem ; int ret ; ret = sem_post(& sem ); /* semaphore is posted */

Use sema_post(3THR) to atomically increment the semaphore pointed to by sem . When any threads are blocked on the semaphore, one of them is unblocked. (For Solaris threads, see sema_post(3THR).)

Return Values

sem_post() returns zero after completing successfully. Any other return value indicates that an error occurred. When the following condition occurs, the function fails and returns the corresponding value.

EINVAL sem points to an illegal address.

Block on a Semaphore Count

sem_wait(3RT)

Prototype: int sem_wait(sem_t * sem );

#include sem_t sem ; int ret ; ret = sem_wait(& sem ); /* wait for semaphore */

Use sema_wait(3THR) to block the calling thread until the count in the semaphore pointed to by sem becomes greater than zero, then atomically decrement it.

Return Values

sem_wait() returns zero after completing successfully. Any other return value indicates that an error occurred. When any of the following conditions occurs, the function fails and returns the corresponding value.

EINVAL sem points to an illegal address.

EINTR A signal interrupted this function.

Decrement a Semaphore Count

sem_trywait(3RT)

Prototype: int sem_trywait(sem_t * sem );

#include sem_t sem ; int ret ; ret = sem_trywait(& sem ); /* try to wait for semaphore*/

Use sem_trywait(3RT) to try to atomically decrement the count in the semaphore pointed to by sem when the count is greater than zero. This function is a nonblocking version of sem_wait() ; that is it returns immediately if unsuccessful.

Return Values

sem_trywait() returns zero after completing successfully. Any other return value indicates that an error occurred. When any of the following conditions occurs, the function fails and returns the corresponding value.

EINVAL sem points to an illegal address.

EINTR A signal interrupted this function.

EAGAIN The semaphore was already locked, so it cannot be immediately locked by the sem_trywait() operation.

Destroy the Semaphore State

sem_destroy(3RT)

Prototype: int sem_destroy(sem_t * sem );

#include sem_t sem ; int ret ; ret = sem_destroy(& sem ); /* the semaphore is destroyed */

Use sem_destroy(3RT) to destroy any state associated with the semaphore pointed to by sem . The space for storing the semaphore is not freed. (For Solaris threads, see sem_destroy(3THR).)

Return Values

sem_destroy() returns zero after completing successfully. Any other return value indicates that an error occurred. When the following condition occurs, the function fails and returns the corresponding value.

EINVAL sem points to an illegal address.

The Producer/Consumer Problem, Using Semaphores

The data structure in Example 4–14 is similar to that used for the condition variables example (see Example 4–11). Two semaphores represent the number of full and empty buffers and ensure that producers wait until there are empty buffers and that consumers wait until there are full buffers.

Example 4–14 The Producer/Consumer Problem With Semaphores

typedef struct { char buf[BSIZE]; sem_t occupied; sem_t empty; int nextin; int nextout; sem_t pmut; sem_t cmut; } buffer_t; buffer_t buffer; sem_init(&buffer.occupied, 0, 0); sem_init(&buffer.empty,0, BSIZE); sem_init(&buffer.pmut, 0, 1); sem_init(&buffer.cmut, 0, 1); buffer.nextin = buffer.nextout = 0;

Another pair of (binary) semaphores plays the same role as mutexes, controlling access to the buffer when there are multiple producers and multiple empty buffer slots, and when there are multiple consumers and multiple full buffer slots. Mutexes would work better here, but would not provide as good an example of semaphore use.

Example 4–15 The Producer/Consumer Problem—the Producer

void producer(buffer_t *b, char item) { sem_wait(&b->empty); sem_wait(&b->pmut); b->buf[b->nextin] = item; b->nextin++; b->nextin %= BSIZE; sem_post(&b->pmut); sem_post(&b->occupied); }

Example 4–16 The Producer/Consumer Problem—the Consumer

char consumer(buffer_t *b) { char item; sem_wait(&b->occupied); sem_wait(&b->cmut); item = b->buf[b->nextout]; b->nextout++; b->nextout %= BSIZE; sem_post(&b->cmut); sem_post(&b->empty); return(item); }

So you have finished reading the thread semaphore topic article, if you find this article useful, please share it. Thank you very much. See more: Semaphore C#, Mutex lock and semaphore, Counting semaphore, Counting semaphore example in C, Semaphore vs SemaphoreSlim, Mutex semaphore C#, Semaphore OS, Semaphore example in C

Top 16 Thread Semaphore 270 Most Correct Answers

Semaphore Class (System.Threading) | Microsoft Docs

multithreading – What is a semaphore? – Stack Overflow

Semaphores (Multithreaded Programming Guide)

RTOS Phần 5: Semaphore

IBM i: Semaphores and threads

Semaphore (programming) – Wikipedia

Lập trình Concurrent cùng Semaphore | TopDev

Semaphore trong Java – GP Coder (Lập trình Java)

threading â Thread-based parallelism — Python 3.10.5 documentation

Semaphore Class (System.Threading)

What is a semaphore?

Semaphores (Multithreaded Programming Guide)

Leave a Comment Cancel reply

Semaphore Class (System.Threading) | Microsoft Docs

multithreading – What is a semaphore? – Stack Overflow

Semaphores (Multithreaded Programming Guide)

RTOS Phần 5: Semaphore

IBM i: Semaphores and threads

Semaphore (programming) – Wikipedia

Lập trình Concurrent cùng Semaphore | TopDev

Semaphore trong Java – GP Coder (Lập trình Java)

threading â Thread-based parallelism — Python 3.10.5 documentation

Semaphore Class (System.Threading)

What is a semaphore?

Semaphores (Multithreaded Programming Guide)

Leave a Comment Cancel reply

threading â Thread-based parallelism — Python 3.10.5 documentation