introduce write lock for USB channel

lib/serial/GwSerial.cpp

@@ -63,6 +63,7 @@ GwSerial::~GwSerial()
 {
     delete buffer;
     if (readBuffer) delete readBuffer;
+    if (lock != nullptr) vSemaphoreDelete(lock);
 }
 
 String GwSerial::getMode(){
@@ -87,10 +88,14 @@ size_t GwSerial::enqueue(const uint8_t *data, size_t len, bool partial)
 }
 GwBuffer::WriteStatus GwSerial::write(){
     if (! isInitialized()) return GwBuffer::ERROR;
-    size_t numWrite=availableForWrite();          
-    size_t rt=buffer->fetchData(numWrite,[](uint8_t *buffer,size_t len, void *p){
-        return ((GwSerial *)p)->stream->write(buffer,len);
-    },this);
+    size_t rt=0;
+    {
+        GWSYNCHRONIZED(lock);
+        size_t numWrite=availableForWrite();          
+        rt=buffer->fetchData(numWrite,[](uint8_t *buffer,size_t len, void *p){
+            return ((GwSerial *)p)->stream->write(buffer,len);
+        },this);
+    }
     if (rt != 0){
         LOG_DEBUG(GwLog::DEBUG+1,"Serial %d write %d",id,rt);
     }

lib/serial/GwSerial.h

@@ -4,6 +4,7 @@
 #include "GwLog.h"
 #include "GwBuffer.h"
 #include "GwChannelInterface.h"
+#include "GwSynchronized.h"
 #if CONFIG_IDF_TARGET_ESP32C3 || CONFIG_IDF_TARGET_ESP32S3
   #include "hal/usb_serial_jtag_ll.h"
 #endif
@@ -26,8 +27,12 @@ class GwSerial : public GwChannelInterface{
         virtual long getFlushTimeout(){return 2000;}
         virtual int availableForWrite()=0;
         int type=0;
+        SemaphoreHandle_t lock=nullptr;
     public:
         GwSerial(GwLog *logger,Stream *stream,int id,int type,bool allowRead=true);
+        void enableWriteLock(){
+            lock=xSemaphoreCreateMutex();
+        }
         virtual ~GwSerial();
         bool isInitialized();
         virtual size_t sendToClients(const char *buf,int sourceId,bool partial=false);