fix threading, and performance issues across NVQIR and REST helpers

runtime/cudaq/platform/default/rest/helpers/anyon/AnyonServerHelper.cpp

@@ -322,7 +322,8 @@ RestHeaders AnyonServerHelper::getHeaders() { return generateRequestHeader(); }
 
 /// Refresh the api key and refresh-token
 void AnyonServerHelper::refreshTokens(bool force_refresh) {
-  std::mutex m;
+
+  static std::mutex m;
   std::lock_guard<std::mutex> l(m);
   RestClient client;
   auto now = std::chrono::high_resolution_clock::now();
@@ -437,8 +438,15 @@ std::string searchAPIKey(std::string &key, std::string &refreshKey,
     hwConfig = std::string(creds);
   else if (!userSpecifiedConfig.empty())
     hwConfig = userSpecifiedConfig;
-  else
-    hwConfig = std::string(getenv("HOME")) + std::string("/.anyon_config");
+  else {
+
+    const char *home = std::getenv("HOME");
+    if (!home)
+      throw std::runtime_error(
+          "HOME environment variable is not set. Cannot locate Anyon "
+          "credentials file. Set CUDAQ_ANYON_CREDENTIALS to override.");
+    hwConfig = std::string(home) + std::string("/.anyon_config");
+  }
   if (cudaq::fileExists(hwConfig)) {
     findApiKeyInFile(key, hwConfig, refreshKey, timeStr, credentials);
   } else {

runtime/cudaq/platform/default/rest/helpers/iqm/IQMServerHelper.cpp

@@ -187,8 +187,11 @@ void IQMServerHelper::initialize(BackendConfig config) {
   } else {
     // Set alternative iqmclient-cli tokens file path if provided via env var
     auto envTokenFilePath = getenv("IQM_TOKENS_FILE");
+    // FIX(security): guard getenv("HOME") against nullptr (e.g. in containers)
+    const char *homeDir = getenv("HOME");
     auto defaultTokensFilePath =
-        std::string(getenv("HOME")) + "/.cache/iqm-client-cli/tokens.json";
+        homeDir ? std::string(homeDir) + "/.cache/iqm-client-cli/tokens.json"
+                : std::string();
     if (envTokenFilePath) {
       tokensFilePath = std::string(envTokenFilePath);
     } else if (cudaq::fileExists(defaultTokensFilePath)) {
@@ -537,8 +540,9 @@ std::string IQMServerHelper::writeQuantumArchitectureFile(void) {
     fwrite(outputLine.c_str(), outputLine.length(), 1, file);
   }
 
+  // FIX(bug): fclose() already closes the underlying fd from fdopen().
+  // Calling close(fd) after fclose() is a double-close (UB).
   fclose(file);
-  close(fd);
 
   return quantumArchitectureFilePath;
 } // IQMServerHelper::writeQuantumArchitectureFile()

runtime/cudaq/platform/default/rest/helpers/quantinuum/QuantinuumServerHelper.cpp

@@ -245,8 +245,15 @@ static std::string searchAPIKey(std::string &key, std::string &refreshKey,
     hwConfig = std::string(creds);
   else if (!userSpecifiedConfig.empty())
     hwConfig = userSpecifiedConfig;
-  else
-    hwConfig = std::string(getenv("HOME")) + std::string("/.quantinuum_config");
+  else {
+    // FIX(security): guard getenv("HOME") against nullptr (e.g. in containers)
+    const char *home = std::getenv("HOME");
+    if (!home)
+      throw std::runtime_error(
+          "HOME environment variable is not set. Cannot locate Quantinuum "
+          "credentials file. Set CUDAQ_QUANTINUUM_CREDENTIALS to override.");
+    hwConfig = std::string(home) + std::string("/.quantinuum_config");
+  }
   if (cudaq::fileExists(hwConfig)) {
     findApiKeyInFile(key, hwConfig, refreshKey, timeStr);
   } else {
@@ -705,7 +712,9 @@ void QuantinuumServerHelper::refreshTokens(bool force_refresh) {
     throw std::runtime_error(
         "Cannot get refresh access token, refresh key is empty.");
   }
-  std::mutex m;
+  // FIX(bug): mutex must be static to provide actual cross-thread protection.
+  // A local mutex is created/destroyed per call, giving zero synchronization.
+  static std::mutex m;
   std::lock_guard<std::mutex> l(m);
   auto now = std::chrono::high_resolution_clock::now();
 

runtime/nvqir/NVQIR.cpp

@@ -222,8 +222,9 @@ constexpr std::string_view typeName() {
 template <SimPrecisionType To, SimPrecisionType From>
 std::unique_ptr<std::complex<To>[]> convertToComplex(std::complex<From> *data,
                                                      std::size_t numQubits) {
-  // The state size is `2^numQubits`
-  auto size = pow(2, numQubits);
+  // FIX(perf): use bit-shift instead of floating-point pow() for exact integer
+  // computation — pow() returns double, losing precision for large qubit counts.
+  auto size = static_cast<std::size_t>(1) << numQubits;
   constexpr auto toType = typeName<To>();
   constexpr auto fromType = typeName<From>();
   CUDAQ_INFO("copying {} complex<{}> values to complex<{}>", size, fromType,
@@ -241,8 +242,9 @@ std::unique_ptr<std::complex<To>[]> convertToComplex(std::complex<From> *data,
 template <SimPrecisionType To, SimPrecisionType From>
 std::unique_ptr<std::complex<To>[]> convertToComplex(From *data,
                                                      std::size_t numQubits) {
-  // The state size is `2^numQubits`
-  auto size = pow(2, numQubits);
+  // FIX(perf): use bit-shift instead of floating-point pow() for exact integer
+  // computation — pow() returns double, losing precision for large qubit counts.
+  auto size = static_cast<std::size_t>(1) << numQubits;
   constexpr auto toType = typeName<To>();
   constexpr auto fromType = typeName<From>();
   CUDAQ_INFO("copying {} {} values to complex<{}>", size, fromType, toType);
@@ -431,8 +433,9 @@ void __quantum__rt__qubit_release_array(Array *arr) {
     nvqir::getCircuitSimulatorInternal()->deallocate(idxVal->idx);
     delete idxVal;
   }
-  delete arr;
+  // FIX(bug): untrack before delete to avoid use-after-delete on dangling ptr
   nvqir::ArrayTracker::getInstance().untrack(arr);
+  delete arr;
   return;
 }
 
@@ -828,6 +831,10 @@ void __quantum__qis__apply_kraus_channel_double(std::int64_t krausChannelKey,
       try {
         channelName = noise->get_channel(key, paramVec).get_type_name();
       } catch (...) {
+
+        CUDAQ_DBG("Failed to resolve noise channel name in tracer mode for "
+                  "key {}, falling back to 'apply_noise'",
+                  key);
       }
     }
     ctx->kernelTrace.appendNoiseInstruction(
@@ -869,6 +876,10 @@ __quantum__qis__apply_kraus_channel_float(std::int64_t krausChannelKey,
       try {
         channelName = noise->get_channel(key, paramVec).get_type_name();
       } catch (...) {
+
+        CUDAQ_DBG("Failed to resolve noise channel name in tracer mode for "
+                  "key {}, falling back to 'apply_noise'",
+                  key);
       }
     }
     ctx->kernelTrace.appendNoiseInstruction(
@@ -975,7 +986,7 @@ std::vector<details::FakeQubit> *
 __quantum__qis__convert_array_to_stdvector(Array *arr) {
   const std::size_t size = arr->size();
   std::vector<details::FakeQubit> *result = new std::vector<details::FakeQubit>;
-  result->reserve(size);
+  result->resize(size);
   for (std::size_t i = 0; i < size; ++i) {
     (*result)[i].id = (*arr)[i];
     (*result)[i].negated = false;