From afbc049cc91e91bbd8f50586fdfb3ce874d3f91e Mon Sep 17 00:00:00 2001
From: Christopher Pascoe <alltheblinkythings@gmail.com>
Date: Wed, 9 Dec 2015 22:51:57 -0800
Subject: [PATCH 1/2] Make the circular buffer's _size and _bufend members
 immutable.

---
 cores/esp8266/cbuf.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cores/esp8266/cbuf.h b/cores/esp8266/cbuf.h
index 087e7200b..02b612c5c 100644
--- a/cores/esp8266/cbuf.h
+++ b/cores/esp8266/cbuf.h
@@ -113,9 +113,9 @@ class cbuf {
             return (ptr == _bufend) ? _buf : ptr;
         }
 
-        size_t _size;
+        const size_t _size;
         char* _buf;
-        char* _bufend;
+        const char* const _bufend;
         char* _begin;
         char* _end;
 };

From 55e0dab799653d7e16f262e3693195570e068854 Mon Sep 17 00:00:00 2001
From: Christopher Pascoe <alltheblinkythings@gmail.com>
Date: Sun, 13 Dec 2015 19:39:47 -0800
Subject: [PATCH 2/2] Protect HardwareSerial's cbuf usage with InterruptLock.

---
 cores/esp8266/HardwareSerial.cpp | 40 +++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 11 deletions(-)

diff --git a/cores/esp8266/HardwareSerial.cpp b/cores/esp8266/HardwareSerial.cpp
index 78108bee7..3527b4a86 100644
--- a/cores/esp8266/HardwareSerial.cpp
+++ b/cores/esp8266/HardwareSerial.cpp
@@ -29,6 +29,7 @@
 #include <inttypes.h>
 #include "Arduino.h"
 #include "cbuf.h"
+#include "interrupts.h"
 
 extern "C" {
 #include "osapi.h"
@@ -556,6 +557,7 @@ int HardwareSerial::available(void) {
     int result = 0;
 
     if (_uart != NULL && _uart->rxEnabled) {
+        InterruptLock il;
         result = static_cast<int>(_rx_buffer->getSize());
     }
 
@@ -570,6 +572,7 @@ int HardwareSerial::peek(void) {
     if(_uart == 0)
         return -1;
     if(_uart->rxEnabled) {
+        InterruptLock il;
         return _rx_buffer->peek();
     } else {
         return -1;
@@ -580,6 +583,7 @@ int HardwareSerial::read(void) {
     if(_uart == 0)
         return -1;
     if(_uart->rxEnabled) {
+        InterruptLock il;
         return _rx_buffer->read();
     } else {
         return -1;
@@ -590,6 +594,7 @@ int HardwareSerial::availableForWrite(void) {
     if(_uart == 0)
         return 0;
     if(_uart->txEnabled) {
+        InterruptLock il;
         return static_cast<int>(_tx_buffer->room());
     } else {
         return 0;
@@ -604,9 +609,16 @@ void HardwareSerial::flush() {
     if(!_written)
         return;
 
-    while(_tx_buffer->getSize() || uart_get_tx_fifo_room(_uart) < UART_TX_FIFO_SIZE)
+    while(true) {
+        {
+            InterruptLock il;
+            if(_tx_buffer->getSize() == 0 &&
+               uart_get_tx_fifo_room(_uart) >= UART_TX_FIFO_SIZE) {
+                break;
+            }
+        }
         yield();
-
+    }
     _written = false;
 }
 
@@ -614,18 +626,24 @@ size_t HardwareSerial::write(uint8_t c) {
     if(_uart == 0 || !_uart->txEnabled)
         return 0;
     _written = true;
-    size_t room = uart_get_tx_fifo_room(_uart);
-    if(room > 0 && _tx_buffer->empty()) {
-        uart_transmit_char(_uart, c);
-        return 1;
-    }
 
-    while(_tx_buffer->room() == 0) {
+    while(true) {
+        {
+            InterruptLock il;
+            if(_tx_buffer->empty()) {
+                if(uart_get_tx_fifo_room(_uart) > 0) {
+                    uart_transmit_char(_uart, c);
+                } else {
+                    _tx_buffer->write(c);
+                    uart_arm_tx_interrupt(_uart);
+                }
+                break;
+            } else if(_tx_buffer->write(c)) {
+                break;
+            }
+        }
         yield();
     }
-
-    _tx_buffer->write(c);
-    uart_arm_tx_interrupt(_uart);
     return 1;
 }