How Can Reader/Writer Locks in C Optimize Concurrent Access for Frequent Readers and Infrequent Writers?

Reader/Writer Locks in C : An Efficient Solution for Frequent Readers and Infrequent Writers

In C , reader/writer locks are a crucial synchronization primitive designed to optimize concurrent access to shared data by multiple threads. A use case that often benefits from reader/writer locks is when there is a single, infrequent writer and many frequent readers. This article explores the standard C approach to implementing reader/writer locks and an alternative using Boost for older compiler versions.

Standard C Solution (C 14)

The preferred cross-platform solution in modern C versions (since C 14 and VS2015) is to leverage the standard library's header. This provides the following lock types:

• std::shared_mutex (aka Lock): The base lock class
• std::unique_lock (aka WriteLock): A unique lock that allows exclusive write access to the shared data
• std::shared_lock (aka ReadLock): A shared lock that allows concurrent read access to the shared data

Boost Solution for Older Versions

For older compiler versions and standards, a robust alternative is to use the Boost threading library. Boost provides the following lock types:

• boost::shared_mutex (aka Lock): The base lock class
• boost::unique_lock (aka WriteLock): A unique lock that allows exclusive write access to the shared data
• boost::shared_lock (aka ReadLock): A shared lock that allows concurrent read access to the shared data

Example Usage

Here's how to use both the standard C and Boost solutions:

Standard C (C 14):

#include <shared_mutex>

typedef std::shared_mutex Lock;
typedef std::unique_lock< Lock > WriteLock;
typedef std::shared_lock< Lock > ReadLock;

Lock myLock;

void ReadFunction()
{
    ReadLock r_lock(myLock);
    // Do reader stuff
}

void WriteFunction()
{
    WriteLock w_lock(myLock);
    // Do writer stuff
}

Boost:

#include <boost/thread/locks.hpp>
#include <boost/thread/shared_mutex.hpp>

typedef boost::shared_mutex Lock;
typedef boost::unique_lock< Lock > WriteLock;
typedef boost::shared_lock< Lock > ReadLock;

Lock myLock;

void ReadFunction()
{
    ReadLock r_lock(myLock);
    // Do reader stuff
}

void WriteFunction()
{
    WriteLock w_lock(myLock);
    // Do writer stuff
}

By selecting the appropriate solution based on your platform and C version, you can efficiently manage shared resources and optimize performance for your concurrent applications where there are many more readers than writers.

The above is the detailed content of How Can Reader/Writer Locks in C Optimize Concurrent Access for Frequent Readers and Infrequent Writers?. For more information, please follow other related articles on the PHP Chinese website!