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--- gist-semaphores [February 06, 2026 at 01:09] – yanevskiv
+++ gist-semaphores [May 14, 2026 at 11:38] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+# (WIP) Semaphores (Examples)
+This page includes some examples of semaphores in multi-threading environments. The syntax is borrowed from [[EasyMT]].
+## Basic
+### Synchronization
+Two threads `a()` and `b()` alternate their execution regardless of the scheduler.
+Output: `abababababab...`
+```c
+Sem sa = 1, sb = 0;
+void a() {
+    while (true) {
+        wait(sa);
+        printf("a")
+        signal(sb);
+    }
+}
+void b() {
+    while (true) {
+        wait(sb);
+        printf("b");
+        signal(sa);
+    }
+}
+```
+### Critical Section & Mutex
+Threads **a()** and **b()** are not allowed to execute `// ... CRITICAL SECTION ...` at the same time.
+The issue is resolved by using a mutex semaphore.
+```c
+Sem mutex = 1;
+void a() {
+    while (true) {
+        wait(mutex);
+        //... CRITICAL SECTION ...
+		signal(mutex);
+        usleep(50);
+    }
+}
+void b() {
+    while (true) {
+        wait(mutex);
+        // ... CRITICAL SECTION ...
+		signal(mutex);
+        usleep(50);
+    }
+}
+```
+### Producer & Consumer / Bounded Buffer
+There is a global buffer of a bounded capacity $B$.
+"Producers" produce and append data to the head. They are not allowed to put more items than $B$ in the buffer.
+"Consumers" take and consume data from the buffer. They are not take data from the buffer if the buffer is empty.
+The issue is resolved by using two synchronization semaphores `full` and `empty` and one `mutex` semaphore to guard the common buffer.
+It is, however, possible to use two mutexes `mutex_consumer` and `mutex_producer` if the buffer is implemented in a way
+```c
+#define B 10 /* buffer capacity */
+Buffer buffer;
+Sem mutex = 1;
+Sem full = B;
+Sem empty = 0;
+void producer(int id) {
+    while (true) {
+        Data data = produce_data();
+        wait(full);
+        wait(mutex);
+        put_data(buffer, data)
+        signal(mutex);
+        signal(empty);
+    }
+}
+void consumer(int id) {
+    while (true) {
+        wait(empty);
+        wait(mutex);
+        Data data = get_data(buffer);
+        signal(mutex);
+        signal(full);
+        consume_data(data);
+    }
+}
+```