Hardware:

Board: DOIT ESP32 DEVKIT v1
Core Installation version: 1_0_6
IDF Version: 3.3.5-1-g85c43024c
IDE name: VS Code with platform.io
Flash Frequency: 40MHz
PSRAM enabled: no
Upload Speed: 115200
Computer OS: macOS

Description:

I am experiencing race conditions with HardwareSerial.available() and HardwareSerial.read(). The following single-threaded code is returning -1 from HardwareSerial.read(), which shouldn't be possible after checking that HardwareSerial.available() > 0.

This seems to be caused by the underlying HAL uartAvailable() function.

Sketch:

//Change the code below by your sketch
#include <Arduino.h>

void setup() {
    Serial.begin(115200);
}

void loop() {
    if (Serial.available() > 0) {
        int b = Serial.read();
        if (b == -1) {
            Serial.println("error reading");
        }
    }
    doOtherStuff()
}

Expected result: Nothing output on serial console
Actual result: Eventually "error reading" output on serial console

Possible cause

This issue seems to be caused by a race condition with the following line:

I think that uartAvailable() should turn off interrupts and call UART_MUTEX_LOCK() in order to avoid the race condition.