nr,slot_worker: add mutex to protect class from concurrent access

detected during debug while slot_worker was still initialized on the
main process, the PHY workers were already running and accessing
class members

srsenb/hdr/phy/nr/slot_worker.h

@@ -86,6 +86,7 @@ private:
   srsran_gnb_ul_t                                gnb_ul      = {};
   std::vector<cf_t*>                             tx_buffer; ///< Baseband transmit buffers
   std::vector<cf_t*>                             rx_buffer; ///< Baseband receive buffers
+  std::mutex mutex; ///< Protect concurrent access from workers (and main process that inits the class)
 };
 
 } // namespace nr

srsenb/src/phy/nr/slot_worker.cc

@@ -27,6 +27,8 @@ slot_worker::slot_worker(srsran::phy_common_interface& common_,
 
 bool slot_worker::init(const args_t& args)
 {
+  std::lock_guard<std::mutex> lock(mutex);
+
   // Calculate subframe length
   sf_len = SRSRAN_SF_LEN_PRB_NR(args.nof_max_prb);
 
@@ -104,6 +106,7 @@ slot_worker::~slot_worker()
 
 cf_t* slot_worker::get_buffer_rx(uint32_t antenna_idx)
 {
+  std::lock_guard<std::mutex> lock(mutex);
   if (antenna_idx >= (uint32_t)rx_buffer.size()) {
     return nullptr;
   }
@@ -113,6 +116,7 @@ cf_t* slot_worker::get_buffer_rx(uint32_t antenna_idx)
 
 cf_t* slot_worker::get_buffer_tx(uint32_t antenna_idx)
 {
+  std::lock_guard<std::mutex> lock(mutex);
   if (antenna_idx >= (uint32_t)tx_buffer.size()) {
     return nullptr;
   }