Missing in Modern C++: Event Synchronization Primitive — with Working Examples – ██FR█████ █INTELL███████████

This content originally appeared on DEV Community and was authored by Artak Avetyan

If you’ve ever struggled with mutexes, predicates, and spurious wakeups in C++ multithreaded code, you know how much time can be lost managing synchronization instead of solving real problems. Here’s a simpler, more predictable approach.

std::condition_variable is powerful, but it’s verbose, fragile, and full of boilerplate.

Check the official example in cppreference:

mutexes, predicates, loops, unlock/relock dance — and still you’re exposed to spurious wakeups (proof). Boost and Qt inherit the same quirks.

For developers seeking a straightforward signaling primitive, Windows long offered Event objects, with auto-reset and manual-reset semantics to directly signal threads.

The Areg Framework brings the same concept to cross-platform C++: SynchEvent, a lightweight, developer-friendly multithreading primitive that behaves like Windows Events and works well even in embedded systems.

Why SynchEvent?

Think of it as a direct C++ event primitive:

No spurious wakeups
No predicate gymnastics
No unlock/relock pitfalls

Just signal and wait — with both auto-reset and manual-reset semantics, like Windows Events.

Key Features

SynchEvent is modeled after Windows Events, but works on Linux and Windows alike:

Auto-reset → wakes exactly one thread, then resets automatically
Manual-reset → wakes all waiters until reset
Persistent state → no lost signals (signal-before-wait still wakes)
Straightforward API → lock(), unlock(), setEvent(), resetEvent()

No extra flags, mutexes, or predicate loops required.

Auto-reset vs Manual-reset (visual)

Auto-reset (wake ONE, then reset):
   [Thread A waits] ---+
   [Thread B waits] ---+--> Signal --> wakes one thread --> reset

Manual-reset (wake ALL until reset):
   [Thread A waits] ---+
   [Thread B waits] ---+--> Signal --> wakes all threads --> stays signaled

Code Comparison

With `std::condition_variable`

Example from cppreference

std::mutex m;
std::condition_variable cv;
std::string data;
bool ready = false;
bool processed = false;

void worker() {
    std::unique_lock lk(m);
    cv.wait(lk, []{ return ready; });
    data += " processed";
    processed = true;
    lk.unlock();
    cv.notify_one();
}

int main() {
    data = "Example";
    std::thread worker(worker);

    { std::lock_guard lk(m); ready = true; }
    cv.notify_one();

    { std::unique_lock lk(m); cv.wait(lk, []{ return processed; }); }

    worker.join();
    std::cout << data << '\n';
}

With `SynchEvent` (Areg SDK)

Full example here

#include "areg/base/SynchObjects.hpp"

SynchEvent gEvent(false, true); // signaled, auto-reset
std::string data;

void workerThread() {
    gEvent.lock();         // wait (no spurious wakeups, no predicate loops)
    data += " processed";
    gEvent.setEvent();     // signal done
}

int main() {
    data = "Example";
    std::thread worker(workerThread);

    gEvent.setEvent();     // signal worker
    gEvent.lock();         // wait for completion

    worker.join();
    std::cout << data << '\n';
}

Notice the difference: no flags, no spurious wakeups, no lock dance.

Another example demonstrates waiting on multiple mixed synchronization objects like SynchEvent and Mutex. Clone the repo and try it yourself to see the simplicity firsthand.

Feature	Areg SynchEvent	std::condition_variable	Win Event	POCO::Event
Auto-reset	Wakes one thread	Manual logic	Wakes one	Wakes one
Manual-reset	Wakes all threads	Not supported	Wakes all	Wakes all
Initial state	Persistent	Not persistent	Persistent	Not persistent
Reliable wakeups	Guaranteed	Spurious possible	Not guaranteed	Not guaranteed
Boilerplate	Minimal API	Verbose	Low	Low
Multi-event wait	Native support	Complex	Supported	Not supported
Mix with mutex	Fully supported	Custom logic	Supported	Not supported
Cross-platform	Windows & Linux	STL/Boost	Windows only	Windows & Linux
Ease of use	Simple & flexible	Verbose, error-prone	Simple	Simple

Legend: = supported, = problematic, = not available

Where SynchEvent Shines

A classic use case for a synchronization event is a Message Queue:

Queue has a manual-reset event
As long as messages exist → event stays signaled
When last message is consumed → event resets

With condition_variable, this requires extra locks, predicates, and loop checks.
With SynchEvent, it’s a single signal/wait mechanism.

Condition variables are fine for state predicates, but for pure synchronization, SynchEvent is the sharper tool.

Final Takeaway

If you’re tired of condition-variable spaghetti, try SynchEvent from Areg Framework: cross-platform, lightweight, and modeled after Windows Events.

Star the Areg SDK repo on GitHub, try the examples, and experience how effortless C++ multithreading can be!