我会用一些例子来解释:

Lock:使用Lock的一个例子是将项目(必须有唯一键)添加到共享字典中。 锁将确保当另一个线程(处于临界区)已经通过检查并正在添加项时，一个线程不会进入检查字典中是否存在项的代码机制。如果另一个线程试图输入一个锁定的代码，它将等待(被阻塞)，直到对象被释放。

private static readonly Object obj = new Object();

lock (obj) //after object is locked no thread can come in and insert item into dictionary on a different thread right before other thread passed the check...
{
    if (!sharedDict.ContainsKey(key))
    {
        sharedDict.Add(item);
    }
}

信号量: 假设您有一个连接池，那么单个线程可以通过等待信号量获得连接来在池中保留一个元素。然后它使用连接，工作完成后通过释放信号量来释放连接。

我喜欢的代码示例是@Patric给出的一个bouncer -在这里:

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;

namespace TheNightclub
{
    public class Program
    {
        public static Semaphore Bouncer { get; set; }

        public static void Main(string[] args)
        {
            // Create the semaphore with 3 slots, where 3 are available.
            Bouncer = new Semaphore(3, 3);

            // Open the nightclub.
            OpenNightclub();
        }

        public static void OpenNightclub()
        {
            for (int i = 1; i <= 50; i++)
            {
                // Let each guest enter on an own thread.
                Thread thread = new Thread(new ParameterizedThreadStart(Guest));
                thread.Start(i);
            }
        }

        public static void Guest(object args)
        {
            // Wait to enter the nightclub (a semaphore to be released).
            Console.WriteLine("Guest {0} is waiting to entering nightclub.", args);
            Bouncer.WaitOne();          

            // Do some dancing.
            Console.WriteLine("Guest {0} is doing some dancing.", args);
            Thread.Sleep(500);

            // Let one guest out (release one semaphore).
            Console.WriteLine("Guest {0} is leaving the nightclub.", args);
            Bouncer.Release(1);
        }
    }
}

互斥量基本上就是信号量(1,1)，并且经常在全局范围内使用(应用范围内使用，否则可以说锁更合适)。当从全局可访问的列表中删除节点时，可以使用全局互斥(在删除节点时，最不希望另一个线程做一些事情)。当你获得互斥锁时，如果不同的线程试图获得同一个互斥锁，它将被置于睡眠状态，直到获得互斥锁的同一线程释放它。

@deepe是创建全局互斥的一个很好的例子

class SingleGlobalInstance : IDisposable
{
    public bool hasHandle = false;
    Mutex mutex;

    private void InitMutex()
    {
        string appGuid = ((GuidAttribute)Assembly.GetExecutingAssembly().GetCustomAttributes(typeof(GuidAttribute), false).GetValue(0)).Value.ToString();
        string mutexId = string.Format("Global\\{{{0}}}", appGuid);
        mutex = new Mutex(false, mutexId);

        var allowEveryoneRule = new MutexAccessRule(new SecurityIdentifier(WellKnownSidType.WorldSid, null), MutexRights.FullControl, AccessControlType.Allow);
        var securitySettings = new MutexSecurity();
        securitySettings.AddAccessRule(allowEveryoneRule);
        mutex.SetAccessControl(securitySettings);
    }

    public SingleGlobalInstance(int timeOut)
    {
        InitMutex();
        try
        {
            if(timeOut < 0)
                hasHandle = mutex.WaitOne(Timeout.Infinite, false);
            else
                hasHandle = mutex.WaitOne(timeOut, false);

            if (hasHandle == false)
                throw new TimeoutException("Timeout waiting for exclusive access on SingleInstance");
        }
        catch (AbandonedMutexException)
        {
            hasHandle = true;
        }
    }


    public void Dispose()
    {
        if (mutex != null)
        {
            if (hasHandle)
                mutex.ReleaseMutex();
            mutex.Dispose();
        }
    }
}

然后用like:

using (new SingleGlobalInstance(1000)) //1000ms timeout on global lock
{
    //Only 1 of these runs at a time
    GlobalNodeList.Remove(node)
}

希望这能为您节省一些时间。

我的理解是互斥量只能在单个进程中使用，但可以跨多个线程使用，而信号量可以跨多个进程和它们对应的线程集使用。

此外，互斥是二进制的(它要么被锁定要么被解锁)，而信号量有计数的概念，或者一个包含多个锁定和解锁请求的队列。

有人能证实我的解释吗?我说的是Linux环境，特别是使用内核2.6.32的Red Hat Enterprise Linux (RHEL)版本6。

大多数问题都可以用(i)锁，(ii)信号量来解决……，或(iii)两者的组合!正如您可能已经发现的，它们非常相似:都防止竞争条件，都有acquire()/release()操作，都导致零或多个线程被阻塞/怀疑…… 实际上，关键的区别仅仅在于它们如何锁定和解锁。

A lock (or mutex) has two states (0 or 1). It can be either unlocked or locked. They're often used to ensure only one thread enters a critical section at a time. A semaphore has many states (0, 1, 2, ...). It can be locked (state 0) or unlocked (states 1, 2, 3, ...). One or more semaphores are often used together to ensure that only one thread enters a critical section precisely when the number of units of some resource has/hasn't reached a particular value (either via counting down to that value or counting up to that value).

对于这两个锁/信号量，在原语处于状态0时试图调用acquire()会导致调用线程挂起。对于锁——获取状态为1的锁的尝试是成功的。对于信号量——尝试获取状态{1,2,3，…是成功的。

对于状态为0的锁，如果之前调用acquire()的同一个线程现在调用release，则释放成功。如果一个不同的线程尝试了这个操作，那么将由实现/库决定发生什么(通常是忽略尝试或抛出错误)。对于处于状态0的信号量，任何线程都可以调用release，并且它将成功(不管之前哪个线程使用acquire将信号量置于状态0)。

从前面的讨论中，我们可以看到锁有一个所有者的概念(唯一可以调用释放的线程是所有者)，而信号量没有所有者(任何线程都可以在信号量上调用释放)。

造成很多困惑的是，在实践中，它们是这个高级定义的许多变体。

需要考虑的重要变化:

acquire()/release()应该被称为什么?—[变化很大] 您的锁/信号量是否使用“队列”或“集”来记住等待的线程? 你的锁/信号量可以与其他进程的线程共享吗? 你的锁是“可重入的”吗?——[通常是的]。 你的锁是“阻塞/非阻塞”吗?-[通常非阻塞锁被用作阻塞锁(又名自旋锁)，导致繁忙等待]。 如何确保操作是“原子的”?

这取决于你的书/讲师/语言/图书馆/环境。 下面是一些语言是如何回答这些细节的。

C, C+ (pthreads)

A mutex is implemented via pthread_mutex_t. By default, they can't be shared with any other processes (PTHREAD_PROCESS_PRIVATE), however mutex's have an attribute called pshared. When set, so the mutex is shared between processes (PTHREAD_PROCESS_SHARED). A lock is the same thing as a mutex. A semaphore is implemented via sem_t. Similar to mutexes, semaphores can be shared between threasds of many processes or kept private to the threads of one single process. This depends on the pshared argument provided to sem_init.

python (threading.py)

A lock (threading.RLock) is mostly the same as C/C++ pthread_mutex_ts. Both are both reentrant. This means they may only be unlocked by the same thread that locked it. It is the case that sem_t semaphores, threading.Semaphore semaphores and theading.Lock locks are not reentrant -- for it is the case any thread can perform unlock the lock / down the semaphore. A mutex is the same as a lock (the term is not used often in python). A semaphore (threading.Semaphore) is mostly the same as sem_t. Although with sem_t, a queue of thread ids is used to remember the order in which threads became blocked when attempting to lock it while it is locked. When a thread unlocks a semaphore, the first thread in the queue (if there is one) is chosen to be the new owner. The thread identifier is taken off the queue and the semaphore becomes locked again. However, with threading.Semaphore, a set is used instead of a queue, so the order in which threads became blocked is not stored -- any thread in the set may be chosen to be the next owner.

Java (Java . util . concurrent)

A lock (java.util.concurrent.ReentrantLock) is mostly the same as C/C++ pthread_mutex_t's, and Python's threading.RLock in that it also implements a reentrant lock. Sharing locks between processes is harder in Java because of the JVM acting as an intermediary. If a thread tries to unlock a lock it doesn't own, an IllegalMonitorStateException is thrown. A mutex is the same as a lock (the term is not used often in Java). A semaphore (java.util.concurrent.Semaphore) is mostly the same as sem_t and threading.Semaphore. The constructor for Java semaphores accept a fairness boolean parameter that control whether to use a set (false) or a queue (true) for storing the waiting threads.

理论上，信号量经常被讨论，但在实践中，信号量的使用并不多。一个信号量只保存一个整数的状态，所以它通常是相当不灵活的，并且需要同时使用许多个，这导致理解代码的困难。此外，任何线程都可以释放信号量的事实有时是不希望看到的。取而代之的是更多面向对象/高级同步原语/抽象，如“条件变量”和“监视器”。

看一看John Kopplin的多线程教程。

在线程间同步一节中，他解释了事件、锁、互斥量、信号量和可等待计时器之间的区别

A mutex can be owned by only one thread at a time, enabling threads to coordinate mutually exclusive access to a shared resource Critical section objects provide synchronization similar to that provided by mutex objects, except that critical section objects can be used only by the threads of a single process Another difference between a mutex and a critical section is that if the critical section object is currently owned by another thread, EnterCriticalSection() waits indefinitely for ownership whereas WaitForSingleObject(), which is used with a mutex, allows you to specify a timeout A semaphore maintains a count between zero and some maximum value, limiting the number of threads that are simultaneously accessing a shared resource.

我会用一些例子来解释:

Lock:使用Lock的一个例子是将项目(必须有唯一键)添加到共享字典中。 锁将确保当另一个线程(处于临界区)已经通过检查并正在添加项时，一个线程不会进入检查字典中是否存在项的代码机制。如果另一个线程试图输入一个锁定的代码，它将等待(被阻塞)，直到对象被释放。

private static readonly Object obj = new Object();

lock (obj) //after object is locked no thread can come in and insert item into dictionary on a different thread right before other thread passed the check...
{
    if (!sharedDict.ContainsKey(key))
    {
        sharedDict.Add(item);
    }
}

信号量: 假设您有一个连接池，那么单个线程可以通过等待信号量获得连接来在池中保留一个元素。然后它使用连接，工作完成后通过释放信号量来释放连接。

我喜欢的代码示例是@Patric给出的一个bouncer -在这里:

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;

namespace TheNightclub
{
    public class Program
    {
        public static Semaphore Bouncer { get; set; }

        public static void Main(string[] args)
        {
            // Create the semaphore with 3 slots, where 3 are available.
            Bouncer = new Semaphore(3, 3);

            // Open the nightclub.
            OpenNightclub();
        }

        public static void OpenNightclub()
        {
            for (int i = 1; i <= 50; i++)
            {
                // Let each guest enter on an own thread.
                Thread thread = new Thread(new ParameterizedThreadStart(Guest));
                thread.Start(i);
            }
        }

        public static void Guest(object args)
        {
            // Wait to enter the nightclub (a semaphore to be released).
            Console.WriteLine("Guest {0} is waiting to entering nightclub.", args);
            Bouncer.WaitOne();          

            // Do some dancing.
            Console.WriteLine("Guest {0} is doing some dancing.", args);
            Thread.Sleep(500);

            // Let one guest out (release one semaphore).
            Console.WriteLine("Guest {0} is leaving the nightclub.", args);
            Bouncer.Release(1);
        }
    }
}

互斥量基本上就是信号量(1,1)，并且经常在全局范围内使用(应用范围内使用，否则可以说锁更合适)。当从全局可访问的列表中删除节点时，可以使用全局互斥(在删除节点时，最不希望另一个线程做一些事情)。当你获得互斥锁时，如果不同的线程试图获得同一个互斥锁，它将被置于睡眠状态，直到获得互斥锁的同一线程释放它。

@deepe是创建全局互斥的一个很好的例子

class SingleGlobalInstance : IDisposable
{
    public bool hasHandle = false;
    Mutex mutex;

    private void InitMutex()
    {
        string appGuid = ((GuidAttribute)Assembly.GetExecutingAssembly().GetCustomAttributes(typeof(GuidAttribute), false).GetValue(0)).Value.ToString();
        string mutexId = string.Format("Global\\{{{0}}}", appGuid);
        mutex = new Mutex(false, mutexId);

        var allowEveryoneRule = new MutexAccessRule(new SecurityIdentifier(WellKnownSidType.WorldSid, null), MutexRights.FullControl, AccessControlType.Allow);
        var securitySettings = new MutexSecurity();
        securitySettings.AddAccessRule(allowEveryoneRule);
        mutex.SetAccessControl(securitySettings);
    }

    public SingleGlobalInstance(int timeOut)
    {
        InitMutex();
        try
        {
            if(timeOut < 0)
                hasHandle = mutex.WaitOne(Timeout.Infinite, false);
            else
                hasHandle = mutex.WaitOne(timeOut, false);

            if (hasHandle == false)
                throw new TimeoutException("Timeout waiting for exclusive access on SingleInstance");
        }
        catch (AbandonedMutexException)
        {
            hasHandle = true;
        }
    }


    public void Dispose()
    {
        if (mutex != null)
        {
            if (hasHandle)
                mutex.ReleaseMutex();
            mutex.Dispose();
        }
    }
}

然后用like:

using (new SingleGlobalInstance(1000)) //1000ms timeout on global lock
{
    //Only 1 of these runs at a time
    GlobalNodeList.Remove(node)
}

希望这能为您节省一些时间。

维基百科有一个关于信号量和互斥量区别的很好的章节:

A mutex is essentially the same thing as a binary semaphore and sometimes uses the same basic implementation. The differences between them are: Mutexes have a concept of an owner, which is the process that locked the mutex. Only the process that locked the mutex can unlock it. In contrast, a semaphore has no concept of an owner. Any process can unlock a semaphore. Unlike semaphores, mutexes provide priority inversion safety. Since the mutex knows its current owner, it is possible to promote the priority of the owner whenever a higher-priority task starts waiting on the mutex. Mutexes also provide deletion safety, where the process holding the mutex cannot be accidentally deleted. Semaphores do not provide this.