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--- critical-sections-openmp [June 11, 2026 at 09:19] – created - external edit 127.0.0.1
+++ critical-sections-openmp [Unknown date] (current) – removed - external edit (Unknown date) 127.0.0.1
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-# Critical sections (OpenMP)
-In POSIX threads, mutual exclusion is explicit: you call `pthread_mutex_lock` before a shared update and `pthread_mutex_unlock` after. **Critical sections** in OpenMP do the same thing with a pragma. The enclosed block is protected by an implicit mutex: only one thread at a time executes it, and threads that arrive while another is inside are blocked until it exits. Unlike [[atomic-openmp|`atomic`]], which is limited to a single read-modify-write operation, `critical` can protect an arbitrary sequence of statements.
-```c
-#pragma omp parallel for
-for (int i = 0; i < N; i++) {
-    int val = expensive_compute(i);
-    #pragma omp critical
-    {
-        if (val > best) {
-            best = val;
-            best_idx = i;
-        }
-    }
-}
-```
-Critical sections can be named (`#pragma omp critical(name)`) so that threads only contend with sections sharing the same name. Two differently-named critical sections can be entered simultaneously by different threads. Unnamed sections all share a single implicit lock, so mixing named and unnamed sections in the same program can cause unexpected serialisation.