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+# Threads
+
+Threads {{hi:threads}} provide a means of representing multiple parallel execution contexts.
+_NNG_ makes use of this concept internally, but also provides for user applications
+to utilize the same thread facilities. This allows one form of {{i:concurrency}} for
+applications.
+
+> [!NOTE]
+> Threads in _NNG_ are built upon platform support, which may be based upon operating
+> system supplied threads, process, or coroutines. The appearance of concurrency does
+> not guarantee true concurrency, and scheduling between threads may not necessarily be
+> pre-emptive. While this will not adversely impact applications that use this facility
+> for I/O bound concurrency, it may not provide good results for purely {{i:CPU-bound}} operations.
+
+> [!IMPORTANT]
+> Thread objects created by this function may not be real system-level
+> threads capable of performing blocking I/O operations using normal blocking system calls.
+> If use of blocking system calls is required (not including APIs provided
+> by the _NNG_ library itself of course), then real OS-specific threads
+> should be created instead (such as with `pthread_create` or similar functions.)
+> Blocking _NNG_ library calls can however be made safely from _NNG_ threads.
+
+> [!TIP]
+> The system may impose limits on the number of threads that can be created.
+> Typically applications should not create more than a dozen of these.
+> If greater concurrency or scalability is needed, consider instead using
+> an asynchronous model using [`nng_aio`][aio] structures.
+
+## Thread Structure
+
+```c
+typedef struct nng_thread nng_thread;
+```
+
+The {{i:`nng_thread`}} structure represnts a thread, which is a single execution context.
+A given thread will have its own stack, and CPU registers. However global state, as well
+as values allocated on the heap, will be shared and accessible to all threads in the system
+(See the [Synchronization][synchronization] chapter for functions to help with data sharing between different threads.)
+
+Multiple threads can be thought of as running concurrently, even though
+they might not actually do so.
+
+I/O operations that block (i.e. wait for completion) will block the
+thread, while allowing other threads to proceed.
+
+## Creating a Thread
+
+```c
+int nng_thread_create(nng_thread **thrp, void (*func)(void *), void *arg);
+```
+
+The {{i:`nng_thread_create`}} function creates a thread, which will execute _func_, with
+the given argument _arg_, and returns a pointer to it in _thrp_.
+
+The thread may begin execution immediately.
+
+The thread will persist until _func_ returns.
+
+This function returns zero on success, but may return `NNG_ENOMEM` if insufficient
+resources to create a thread are available.
+
+## Destroying a Thread
+
+```c
+void nng_thread_destroy(nng_thread *thr);
+```
+
+The {{i:`nng_thread_destroy`}} function waits for the thread _thr_ to finish execution.
+This function should be called to reclaim any resources associated with the thread when done.
+It also has the effect of blocking execution in the caller until _thr_ has completed executing.
+
+## Thread Names
+
+```c
+void nng_thread_set_name(nng_thread *thr, const char *name);
+```
+
+In order to facilitate debugging, {{i:`nng_thread_set_name`}} may be called
+to provide a name for the thread. This may change how the thread is represented
+in debuggers. Not all platforms support setting the thread name.
+
+## See Also
+
+[Synchronization][synchronization],
+[Asynchronous Operations][aio]
+
+[synchronization]: ../api/synch.md
+[aio]: TODO.md