fix(native): implement BinarySemaphorePosix with proper pthread synchronization by iannucci · Pull Request #9895 · meshtastic/firmware

iannucci · 2026-03-12T16:38:34Z

Summary

The BinarySemaphorePosix class, used on all Linux/portduino/native builds, has stub implementations that completely break the cooperative thread scheduler:

give() is a no-op (empty function body)
take(uint32_t msec) just calls delay(msec) and always returns false
giveFromISR() is a no-op

The // FIXME comment in take() confirms this was known to be incomplete.

This means the mainDelay semaphore (and any other BinarySemaphorePosix usage) cannot function: threads cannot wake the main loop early via give(), the NotifiedWorkerThread pattern is broken (notify() → mainDelay.interrupt() → give() does nothing), and the scheduler degrades to a fixed-interval poller that always sleeps the full timeout.

What this PR does

Replaces the stubs with a proper binary semaphore implementation using POSIX threads:

Header (BinarySemaphorePosix.h):

Adds #include <pthread.h> (guarded by #ifndef HAS_FREE_RTOS)
Replaces commented-out SemaphoreHandle_t with pthread_mutex_t mutex, pthread_cond_t cond, bool signaled

Implementation (BinarySemaphorePosix.cpp):

Constructor: pthread_mutex_init + pthread_cond_init, signaled = false
Destructor: pthread_cond_destroy + pthread_mutex_destroy
take(msec): pthread_cond_timedwait with CLOCK_REALTIME timeout. Uses a while (!signaled) loop to handle spurious wakeups. Atomically consumes the signal (binary semaphore semantics). Returns true if signaled, false on timeout.
give(): Sets signaled = true, calls pthread_cond_signal under mutex
giveFromISR(): Delegates to give(), sets *pxHigherPriorityTaskWoken = true

Symptoms observed without this fix

Tested on Raspberry Pi 3 Model B (ARM64, Debian 12 Bookworm) with Adafruit LoRa Radio Bonnet (RFM9x/SX1276):

Radio TX works only on fixed timer intervals (no early wake from give())
Radio RX interrupts are not propagated to the main loop
Telemetry packets are sent to the phone API but never transmitted over the mesh
MQTT gateway receives LoRa packets but relay timing is degraded
OLED display (SSD1306 via I2C) was non-functional (likely related to I2C thread scheduling)

After the fix: bidirectional LoRa, MQTT gateway relay, telemetry over mesh, and OLED display all work correctly.

Scope

This change only affects #ifndef HAS_FREE_RTOS builds (Linux/portduino/native). FreeRTOS builds use BinarySemaphoreFreeRTOS and are unaffected.

Test plan

Built with bash ./bin/build-native.sh native (Docker cross-compilation, python:3.11-slim-bookworm, --platform linux/arm64)
Deployed to Raspberry Pi 3 Model B running Debian 12 (Bookworm) ARM64
Verified RF95/SX1276 radio init success
Verified bidirectional LoRa communication (TX and RX confirmed with multiple nodes)
Verified MQTT gateway operation (uplink and downlink)
Verified telemetry transmission over mesh
Verified SSD1306 OLED display working
Verified stable operation across power cycles
Needs testing on other native platforms (x86_64 Linux, macOS simulator)

🤖 Generated with Claude Code

…ronization The BinarySemaphorePosix class (used on all Linux/portduino/native builds) had stub implementations: give() was a no-op and take() just called delay(msec) and returned false. This broke the cooperative thread scheduler on native platforms — threads could not wake the main loop, radio RX interrupts were missed, and telemetry never transmitted over the mesh. Replace the stubs with a proper binary semaphore using pthread_mutex_t + pthread_cond_t + bool signaled: - take(msec): pthread_cond_timedwait with CLOCK_REALTIME timeout, consumes signal atomically (binary semaphore semantics) - give(): sets signaled=true, signals condition variable - giveFromISR(): delegates to give(), sets pxHigherPriorityTaskWoken Tested on Raspberry Pi 3 Model B (ARM64, Debian Bookworm) with Adafruit LoRa Radio Bonnet (SX1276). Before fix: no radio TX/RX, no telemetry on mesh. After fix: bidirectional LoRa, MQTT gateway, telemetry all working. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

github-actions · 2026-03-12T16:38:44Z

@iannucci, Welcome to Meshtastic!

Thanks for opening your first pull request. We really appreciate it.

We discuss work as a team in discord, please join us in the #firmware channel.
There's a big backlog of patches at the moment. If you have time,
please help us with some code review and testing of other PRs!

Welcome to the team 😄

CLAassistant · 2026-03-12T16:38:44Z

All committers have signed the CLA.

GUVWAF · 2026-03-29T15:46:37Z

Very nice work. I believe this might also solve the issue mentioned in #9939, or at least make it way less common, and it is a better solution IMO.

jp-bennett · 2026-03-29T23:21:25Z

It needs to be specific for portduino rather than just any target without HAS_FREE_RTOS, but yes, this looks good.

jp-bennett · 2026-04-12T22:48:08Z

Testing this out with my DMShell branch, and it appears to fix the RX detection issue I was seeing. Which in retrospect is exactly what the PR said it did.

Copilot

Pull request overview

Implements a real POSIX-backed binary semaphore for native/portduino builds to fix cooperative scheduler wakeups (replacing prior stubbed give() / take() behavior).

Changes:

Add pthread_mutex_t/pthread_cond_t state to BinarySemaphorePosix (portduino builds).
Implement take(msec) using pthread_cond_timedwait with binary “consume” semantics.
Implement functional give() and giveFromISR() to wake blocked waits.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
`src/concurrency/BinarySemaphorePosix.h`	Adds pthread-based members/includes for portduino builds.
`src/concurrency/BinarySemaphorePosix.cpp`	Replaces stubs with a pthread mutex/condvar implementation of a binary semaphore.

…ronization (#9895) * fix(native): implement BinarySemaphorePosix with proper pthread synchronization The BinarySemaphorePosix class (used on all Linux/portduino/native builds) had stub implementations: give() was a no-op and take() just called delay(msec) and returned false. This broke the cooperative thread scheduler on native platforms — threads could not wake the main loop, radio RX interrupts were missed, and telemetry never transmitted over the mesh. Replace the stubs with a proper binary semaphore using pthread_mutex_t + pthread_cond_t + bool signaled: - take(msec): pthread_cond_timedwait with CLOCK_REALTIME timeout, consumes signal atomically (binary semaphore semantics) - give(): sets signaled=true, signals condition variable - giveFromISR(): delegates to give(), sets pxHigherPriorityTaskWoken Tested on Raspberry Pi 3 Model B (ARM64, Debian Bookworm) with Adafruit LoRa Radio Bonnet (SX1276). Before fix: no radio TX/RX, no telemetry on mesh. After fix: bidirectional LoRa, MQTT gateway, telemetry all working. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> * ARCH_PORTDUINO * Refactor BinarySemaphorePosix header for ARCH_PORTDUINO * Change preprocessor directive from ifndef to ifdef * Gate new Semaphore code to Portduino and fix STM compilation * Binary Semaphore Posix better error handling --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com> Co-authored-by: Ben Meadors <benmmeadors@gmail.com> Co-authored-by: Jonathan Bennett <jbennett@incomsystems.biz>

…ronization (meshtastic#9895) * fix(native): implement BinarySemaphorePosix with proper pthread synchronization The BinarySemaphorePosix class (used on all Linux/portduino/native builds) had stub implementations: give() was a no-op and take() just called delay(msec) and returned false. This broke the cooperative thread scheduler on native platforms — threads could not wake the main loop, radio RX interrupts were missed, and telemetry never transmitted over the mesh. Replace the stubs with a proper binary semaphore using pthread_mutex_t + pthread_cond_t + bool signaled: - take(msec): pthread_cond_timedwait with CLOCK_REALTIME timeout, consumes signal atomically (binary semaphore semantics) - give(): sets signaled=true, signals condition variable - giveFromISR(): delegates to give(), sets pxHigherPriorityTaskWoken Tested on Raspberry Pi 3 Model B (ARM64, Debian Bookworm) with Adafruit LoRa Radio Bonnet (SX1276). Before fix: no radio TX/RX, no telemetry on mesh. After fix: bidirectional LoRa, MQTT gateway, telemetry all working. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> * ARCH_PORTDUINO * Refactor BinarySemaphorePosix header for ARCH_PORTDUINO * Change preprocessor directive from ifndef to ifdef * Gate new Semaphore code to Portduino and fix STM compilation * Binary Semaphore Posix better error handling --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com> Co-authored-by: Ben Meadors <benmmeadors@gmail.com> Co-authored-by: Jonathan Bennett <jbennett@incomsystems.biz>

github-actions Bot added first-contribution needs-review Needs human review bugfix Pull request that fixes bugs labels Mar 12, 2026

thebentern changed the base branch from master to develop March 12, 2026 18:25

GUVWAF requested a review from jp-bennett March 29, 2026 15:46

Merge branch 'develop' into fix/binary-semaphore-posix

ee88fb1

jp-bennett mentioned this pull request Mar 29, 2026

[Bug]: RPI Zero 2W Linux Native meshtasticd freezes after constant Can not send yet, busyRx #9580

Closed

3 tasks

thebentern and others added 7 commits March 30, 2026 06:52

ARCH_PORTDUINO

86fdc8e

Refactor BinarySemaphorePosix header for ARCH_PORTDUINO

3352f3c

Change preprocessor directive from ifndef to ifdef

c677590

Merge branch 'develop' into fix/binary-semaphore-posix

ced02fa

Merge branch 'develop' into fix/binary-semaphore-posix

d642b20

Merge branch 'develop' into fix/binary-semaphore-posix

72db829

Merge branch 'develop' into fix/binary-semaphore-posix

498503d

Gate new Semaphore code to Portduino and fix STM compilation

bc0dbb0

jp-bennett approved these changes Apr 12, 2026

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thebentern requested a review from Copilot April 12, 2026 23:37

Copilot started reviewing on behalf of thebentern April 12, 2026 23:37 View session

Copilot AI reviewed Apr 12, 2026

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Comment thread src/concurrency/BinarySemaphorePosix.h

Comment thread src/concurrency/BinarySemaphorePosix.cpp

Comment thread src/concurrency/BinarySemaphorePosix.cpp

Comment thread src/concurrency/BinarySemaphorePosix.cpp

Comment thread src/concurrency/BinarySemaphorePosix.cpp

Binary Semaphore Posix better error handling

d1c4cbf

jp-bennett merged commit 4ac74ed into meshtastic:develop Apr 13, 2026
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GUVWAF mentioned this pull request Apr 21, 2026

Fix intermittent busyRx on Portduino SX1262 (stale preamble IRQ) #9939

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fix(native): implement BinarySemaphorePosix with proper pthread synchronization#9895

fix(native): implement BinarySemaphorePosix with proper pthread synchronization#9895
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iannucci commented Mar 12, 2026

Summary

What this PR does

Symptoms observed without this fix

Scope

Test plan

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github-actions Bot commented Mar 12, 2026

@iannucci, Welcome to Meshtastic!

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