![]() If for some reason the first reader doesn’t get the writer mutex, it’s stuck waiting while also holding onto the reader mutex. If successful, the readers hold onto that mutex until there aren’t any readers left. If a reader realizes it’s first, it needs to snag the writer mutex to avoid any shared memory access issues. Notice how the readers variable is used to draw a connection between the readers and writers. On top of all that, we also have to introduce a shared variable which we’ll use to track the number of active readers: procedure reader(): no more readers)Īlso, we have to introduce an additional mutex, so we can start tracking readers in one queue and writers in another queue. With semaphores, the reading process has to be broken into three stages: In other words, if two readers happen to come along when there is nothing writing to our shared resource, we should let both readers read. Since read operations have no affect on a shared resource, we usually allow them to occur concurrently. In general, this will get the job done, but it’s not ideal. Since monitor resources are protected, we can casually call the procedures without worrying about any race conditions: procedure reader(): Then, we setup two procedures: reader and writer. With monitors, the shared resource can be defined inside the monitor. Each procedure is protected by the same mutex: procedure reader(): ![]() With semaphores, we can define two procedures: reader and writer. However, efficiency is not guaranteed as there is no mechanism for process priority. With this solution, correctness is easy to achieve. One way to solve that issue is to organize the reads and writes such that only one process can access shared memory at a time. Orchestrating several readers and writers can be challenging. Each subsection contains a different type of solution which are subsequently organized into subsections by mechanism. In this section, we’ll look at various solutions to the Readers-Writers problem using different process synchronization mechanisms. OSU CSE 6431 Process Synchronization Part 4 (Monitors).OSU CSE 6431 Process Synchronization Part 3 (Semaphores).OSU CSE 6431 Process Synchronization Part 2 (Semaphores).All examples are borrowed from The Ohio State University’s CSE 6431 lecture notes: To be clear, all code in this article will be pseudocode except potential examples leveraging Java’s concurrency features. In this article, we’ll look at a few Readers-Writers scenarios and try to solve them using some of the mechanisms we chatted about last time like semaphores and monitors. readers priority, writers priority, etc.)? In other words, how do we go about scheduling the threads such that we get our desired outcome (i.e. More specifically, the Readers-Writers problem focuses on the challenges related to balancing threads or processes which either wish to read from a shared memory location or write to it. In particular, what sort of rules should we set around shared memory access, so that actions are safe but also efficient? In concurrency, one of the common challenges is balancing who has access to a shared variable. While ((row = csvReader.4 Want to Learn More? Readers-Writers Problem Overview Use the String.split() method to identify the comma delimiter and split the row into fieldsīufferedReader csvReader = new BufferedReader( new FileReader(pathToCsv)).Create a BufferedReader and read the file line by line until an "End of File" ( EOF) character is reached.Let's consider the steps to open a basic CSV file and parse the data it contains: However, not all programs require all of those features, so it is still important to be able to handle CSV files with core Java, without the use of any additional libraries.Ī simple combination of FileReader, BufferedReader, and String.split() can facilitate reading data from CSVs. Third-party parsers define common formats and are able to work with various delimiters, handle special characters, and sometimes even read non-binary data. Owning to the popularity and widespread use of CSV as a format for data transfer, there are many parser libraries that can be used along with Java. This is the first article in a short series dedicated to Libraries for Reading and Writing CSVs in Java.
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