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===Barriers===
{{Main article|Barrier (computer science)}}
Barriers are simple to implement and provide good responsiveness. They are based on the concept of implementing wait cycles to provide synchronization. Consider three threads running simultaneously, starting from barrier 1. After time t, thread1 reaches barrier 2 but it still has to wait for thread 2 and 3 to reach barrier2 as it does not have the correct data. Once all the threads reach barrier 2 they all start again. After time t, thread 1 reaches barrier3 but it will have to wait for threads 2 and 3 and the correct data again.

Thus, in barrier synchronization of multiple threads there will always be a few threads that will end up waiting for other threads as in the above example thread 1 keeps waiting for thread 2 and 3. This results in severe degradation of the process performance.<ref name=":0">{{cite book | doi=10.1109/HPCC.2014.148 | chapter=A Speculative Mechanism for Barrier Synchronization | title=2014 IEEE Intl Conf on High Performance Computing and Communications, 2014 IEEE 6th Intl Symp on Cyberspace Safety and Security, 2014 IEEE 11th Intl Conf on Embedded Software and Syst (HPCC,CSS,ICESS) | date=2014 | last1=Meng | first1=Jinglei | last2=Chen | first2=Tianzhou | last3=Pan | first3=Ping | last4=Yao | first4=Jun | last5=Wu | first5=Minghui | pages=858–865 | isbn=978-1-4799-6123-8 }}</ref>

The barrier synchronization wait function for i<sup>th</sup> thread can be represented as:

(Wbarrier)i=f ((Tbarrier)i, (Rthread)i)

Where Wbarrier is the wait time for a thread, Tbarrier is the number of threads has arrived, and Rthread is the arrival rate of threads.<ref>{{Cite book|doi=10.1109/ICIEV.2012.6317471|isbn=978-1-4673-1154-0|chapter=Process synchronization in multiprocessor and multi-core processor|title=2012 International Conference on Informatics, Electronics & Vision (ICIEV)|pages=554–559|year=2012|last1=Rahman|first1=Mohammed Mahmudur|s2cid=8134329}}</ref>

Experiments show that 34% of the total execution time is spent in waiting for other slower threads.<ref name=":0" />