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    <p><code>mutex 1</code> protects the <code>readcount</code> variable; <code>mutext 2</code> protects <code>writecount</code> variable; mutex <code>r</code> protects the reading operations and mutext <code>w</code> protects the writing operations.</p> <p>1) Let's suppose a writer comes in:</p> <p>Signals <code>mutex 2</code> and increments <code>writercount</code> to account for the extra writer (itself) Since it is the only process that can change <code>writercount</code> (as it is holding <code>mutex 2</code>), it can safely test whether it is the only writer (<code>writercount==1</code>), if true, it signals mutex <code>r</code> to protect readers from coming in -- other writers (<code>writercount &gt; 1</code>) can enjoy the mutex <code>r</code>being signaled already.</p> <p>The writer then signals mutex <code>w</code> to protect its changes from other (concurrent) writers.</p> <p>Last writer (<code>writecount==1</code>) releases mutex <code>r</code> to let readers perform their tasks.</p> <p>2) Let's suppose a reader comes in:</p> <p>Signals <code>mutex 3</code> to protect the readers' setup logic from other readers; then signals mutex <code>r</code> to protect from other writers (remember, <code>r</code> is signaled while writers are operating); then signals <code>mutex 1</code> to protect readcount (from other readers that might be exiting) and if it is the first reader (<code>readercount == 1</code>), signals mutex <code>w</code> to protect from writers (now excludes writers from performing their operations).</p> <p>Reading can be done parallel, so no protection is needed from other readers while reading (remember, mutex <code>w</code> is being held at this point, so no intereference from writers)</p> <p>Then the last reader resets the write mutex (<code>w</code>) to allow writers.</p> <hr> <p>The trick that prevents writer starvation is that writers pose as readers (when signaling mutex <code>p</code>), so have a good chance of getting scheduled even when there are many readers. Also, <code>mutex 3</code> prevents too many readers from waiting on mutex <code>r</code>, so writers have a good chance to signal <code>r</code> when they come.</p>
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    1. POSecond Algorithm Solution to Readers-Writer
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    1. COThanks for the explanation Attila. The write portion makes perfect sense, but the read portion is still unclear to me. Maybe to understand this better you could explain what would happen if there were no mutex 3 and mutex 1 semaphores (only r semaphore remains to protect the readcount)?
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    2. COReadcount is protected by `mutex 1`. `mutex 3` is used to limit the number of concurrent readers waiting on `r` to 1 (to prevent writer starvation). `r` is used to coordinate access between readers and writers
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    3. COmutex 3 is the trickiest part. But well explained!
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