From 3cc3e4e032edd912dd3a55b8df65927e48217f2c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dani=C3=ABl=20van=20de=20Giessen?= <daniel@dvdgiessen.nl>
Date: Wed, 23 Nov 2022 14:20:58 +0100
Subject: [PATCH] esp32/machine_uart: Release GIL for blocking reads.
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If we're reading from an UART with a non-zero timeout, we can release the
GIL so that other threads/tasks may run while we are sleeping waiting for
data to arrive.

Signed-off-by: Daniël van de Giessen <daniel@dvdgiessen.nl>
---
 ports/esp32/machine_uart.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/ports/esp32/machine_uart.c b/ports/esp32/machine_uart.c
index 541d7ccc5..0b4f5890b 100644
--- a/ports/esp32/machine_uart.c
+++ b/ports/esp32/machine_uart.c
@@ -472,8 +472,17 @@ STATIC mp_uint_t machine_uart_read(mp_obj_t self_in, void *buf_in, mp_uint_t siz
         time_to_wait = pdMS_TO_TICKS(self->timeout);
     }
 
+    bool release_gil = time_to_wait > 0;
+    if (release_gil) {
+        MP_THREAD_GIL_EXIT();
+    }
+
     int bytes_read = uart_read_bytes(self->uart_num, buf_in, size, time_to_wait);
 
+    if (release_gil) {
+        MP_THREAD_GIL_ENTER();
+    }
+
     if (bytes_read <= 0) {
         *errcode = MP_EAGAIN;
         return MP_STREAM_ERROR;