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Programming on Multi-Core Processors Using Pthreads (POSIX Threads) |
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Pthreads are defined as a set of C-language programming types and procedure calls,
implemented with a pthread.h header/include file and a thread library.
In many situations, data is read more often than it is modified or written. In these cases,
you can allow threads to read concurrently while holding the lock and allow only one
thread to hold the lock when data is modified. A multiple-reader single-writer lock (or
read-write lock) does this. A read-write lock is acquired either for reading or writing, and
then is released.
A read-write lock allows for a greater level of concurrency in accessing shared data than
that permitted by a mutual exclusion lock. It exploits the fact that while only a single
thread at a time (a writer thread) can modify the shared data, in many cases any number
of threads can concurrently read the data (hence reader threads).
Programs that illustrate the use of Read-Write Lock using different read-write lock APIs
are described.Sample demo code that gives basic idea of how to use Read-Write Lock and
one sample application using both mutex and Read-Write Lock is described so that one can get
better idea of what is exact difference between these synchronization constructs and how to use
them.
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Example 5.1
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Write a sample Pthread program to illustrate the use of Read-Write Lock .
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Example 5.2
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Write a Pthread program to find minimum value in an Integer array using Mutex.
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Example 5.3
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Write a Pthread program to find minimum value in an Integer array using Read Write Lock.
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(Source - References :
Books
Multi-threading
-[MCMTh-01], [MCMTh-02], [MCMTh-I03], [MCMTh-05], [MCMth-09], [MCMth-11],
[MCMTh-15], [MCMTh-21], [MCBW-44] )
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Description of Pthread Programs |
Example 5.1 :
Write a sample Pthread program to illustrate
the use of Read-Write Lock .
( Download source code :
pthread-readwritelock-demo.c
)
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- Objective
Write a Pthread program to illustrate the use of Read-Write Lock.
- Description
This is a very simple program to illustrate the use of Read-Write Lock APIs.
The implementation is as follows: The main thread creates two child threads - rdlockThread and wrlockThread.
The rdlockThread gets the read lock,after it gets it intentionally some wait
time is introduced.
During this time the wrlockThread gets the turn and acquires the
write lock and unlocks it.
Though there is no actual parallelism involved, this is just to demonstrate the working Read-Write lock APIs.
- Input
None
- Output
Sequence of acquiring and releasing Read-Write Lock.
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Example 5.2 :
Write a Pthread program to find the minimum value in an unsorted Integer array using mutex implementation (compare this code with Ex.1.3).
( Download source code :
pthread-findingmin-in-integerlist-mutex.c
)
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- Objective
Write a Pthread program to find the minimum value in an unsorted Integer array
using mutex implementation.
- Description
This is pthread code for finding minimum value in an large integer array. Here array is divided
into different chunks and each thread will find minimum value in its own chunk.
The mutex locks are used to gain exclusive access to the finalminimum value variable. Once this access is gained, the value
is updated as required, and the lock subsequently released. Since at any time, only one thread can hold the lock,
only one thread can update the value
- Input
Array Length, Number of threads
- Output
The minimum value and Execution time.
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Example 5.3 :
Write a Pthread program to find the minimum value in an unsorted Integer using read-write lock implementation.
( Download source code :
pthread-findingmin-in-integerlist-readwrite-locks.c
)
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- Objective
Write a Pthread program to find the minimum value in an unsorted Integer array
using read-write lock implementation.
- Description
This is pthread code for finding minimum value in an large integer array based on read-write locks.
Read-write locks are more suitable for application where frequency of read operation is more than
write operations. So we can see performance improvement if we use read-write lock in such case.
In this example read lock is allowing many threads to check(read) global minimum value and only if
its local minimum value is less than global minimum value it will request write lock and then updates
final value.
- Input
Array Length, Number of threads
- Output
The minimum value and Execution time.
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