Route Java console logging through System.out instead of native stdout

cpp/CMakeLists.txt

@@ -292,11 +292,21 @@ FetchContent_MakeAvailable(papilo)
 
 # PSLP - Lightweight C presolver for linear programs
 # https://github.com/dance858/PSLP
+#
+# v0.0.11 ignores its own verbose=false setting for one message: run_presolver() prints
+# "PSLP declares problem as infeasible[.| or unbounded.]" unconditionally, unlike every other
+# console message in that function, which are all gated on verbose. cuOpt sets verbose = false
+# (see third_party_presolve.cpp) precisely so PSLP stays silent, so this writes unexpectedly
+# straight to the process's native stdout -- observed corrupting Maven Surefire's forked-JVM
+# protocol in the Java bindings, which also uses stdout as its own channel. Patched upstream at
+# https://github.com/dance858/PSLP/pull/55; drop this patch once a release containing it is
+# available and this GIT_TAG is bumped past it.
 FetchContent_Declare(
         pslp
         GIT_REPOSITORY "https://github.com/dance858/PSLP.git"
         GIT_TAG "v0.0.11"
         GIT_PROGRESS TRUE
+        PATCH_COMMAND sh -c "git apply --check '${CMAKE_CURRENT_SOURCE_DIR}/cmake/patches/pslp/respect_verbose_for_infeasible_message.patch' 2>/dev/null && git apply '${CMAKE_CURRENT_SOURCE_DIR}/cmake/patches/pslp/respect_verbose_for_infeasible_message.patch'; true"
         EXCLUDE_FROM_ALL
         SYSTEM
 )

cpp/cmake/patches/pslp/respect_verbose_for_infeasible_message.patch

@@ -0,0 +1,16 @@
+diff --git a/src/core/Presolver.c b/src/core/Presolver.c
+index c0bdc9e..426008e 100644
+--- a/src/core/Presolver.c
++++ b/src/core/Presolver.c
+@@ -720,7 +720,10 @@ PresolveStatus run_presolver(Presolver *presolver)
+     if (status != UNCHANGED)
+     {
+         // problem detected to be infeasible or unbounded
+-        print_infeas_or_unbnd_message(status);
++        if (stgs->verbose)
++        {
++            print_infeas_or_unbnd_message(status);
++        }
+         return status;
+     }
+

cpp/src/utilities/logger.cpp

@@ -1,6 +1,6 @@
 /* clang-format off */
 /*
- * SPDX-FileCopyrightText: Copyright (c) 2025, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ * SPDX-FileCopyrightText: Copyright (c) 2025-2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  */
 /* clang-format on */
@@ -55,6 +55,25 @@ log_buffer& global_log_buffer()
   return buffer;
 }
 
+// Overrides the sink used when log_to_console is true. Null (the default) keeps writing to
+// std::cout; set by language bindings whose host runtime cannot safely receive writes to the
+// native stdout stream -- for example Java, where a raw write there bypasses System.out and can
+// corrupt tools that intercept it, such as Maven Surefire's forked-process protocol.
+static std::mutex g_console_callback_mutex;
+static log_console_callback_t g_console_callback = nullptr;
+
+void set_console_log_callback(log_console_callback_t callback)
+{
+  std::lock_guard<std::mutex> lock(g_console_callback_mutex);
+  g_console_callback = callback;
+}
+
+static log_console_callback_t console_log_callback()
+{
+  std::lock_guard<std::mutex> lock(g_console_callback_mutex);
+  return g_console_callback;
+}
+
 // Callback function for the buffer sink
 static void buffer_log_callback(int lvl, const char* msg)
 {
@@ -161,8 +180,13 @@ init_logger_t::init_logger_t(std::string log_file, bool log_to_console)
 
   // re-initialize sinks
   if (log_to_console) {
-    cuopt::default_logger().sinks().push_back(
-      std::make_shared<rapids_logger::ostream_sink_mt>(std::cout));
+    if (auto callback = console_log_callback(); callback != nullptr) {
+      cuopt::default_logger().sinks().push_back(
+        std::make_shared<rapids_logger::callback_sink_mt>(callback));
+    } else {
+      cuopt::default_logger().sinks().push_back(
+        std::make_shared<rapids_logger::ostream_sink_mt>(std::cout));
+    }
   }
   if (!log_file.empty()) {
     cuopt::default_logger().sinks().push_back(

cpp/src/utilities/logger.hpp

@@ -38,6 +38,19 @@ rapids_logger::logger& default_logger();
  */
 void reset_default_logger();
 
+using log_console_callback_t = void (*)(int level, const char* message);
+
+/**
+ * @brief Overrides the sink used for console logging (settings.log_to_console == true).
+ *
+ * Passing nullptr (the default) restores writing to std::cout. Intended for language bindings
+ * whose host runtime cannot safely receive a raw write to the native stdout stream -- see the
+ * definition site in logger.cpp for why that matters.
+ *
+ * @param callback The callback to invoke for each logged line, or nullptr to restore std::cout.
+ */
+void set_console_log_callback(log_console_callback_t callback);
+
 // Ref-counted logger initializer
 class init_logger_t {
   // Using shared_ptr for ref-counting

java/cuopt/src/main/java/com/nvidia/cuopt/mathematicaloptimization/NativeLogSink.java

@@ -0,0 +1,24 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+package com.nvidia.cuopt.mathematicaloptimization;
+
+/**
+ * Receives cuOpt's console log lines from native code and writes them through {@link
+ * System#out}, rather than the native library writing to the process's stdout stream directly.
+ *
+ * <p>A direct native write bypasses {@code System.out}, so it is invisible to anything that
+ * intercepts or redirects it -- {@link System#setOut}, a logging framework bridge, or Maven
+ * Surefire, which uses the forked JVM's stdout as its own communication channel and can
+ * misinterpret an unexpected raw write on it as the forked process having crashed.
+ *
+ * <p>Called from {@code cuopt_jni.cpp}; not part of the public API.
+ */
+final class NativeLogSink {
+  private NativeLogSink() {}
+
+  static void onLogLine(String message) {
+    System.out.print(message);
+  }
+}

java/cuopt/src/main/native/cuopt_jni.cpp

@@ -19,6 +19,7 @@
 #include <cuopt/mathematical_optimization/io/parser.hpp>
 #include <cuopt/mathematical_optimization/optimization_problem_utils.hpp>
 #include <pdlp/cuopt_c_internal.hpp>
+#include <utilities/logger.hpp>
 
 #include <jni.h>
 
@@ -378,6 +379,57 @@ void mip_set_solution_callback(cuopt_float_t* solution,
   if (detach) { g_jvm->DetachCurrentThread(); }
 }
 
+jclass g_log_sink_class     = nullptr;
+jmethodID g_log_sink_method = nullptr;
+std::once_flag g_log_sink_once;
+
+// cuopt::log_console_callback_t: forwards a console log line to NativeLogSink.onLogLine, so it
+// is written through System.out instead of directly to the native stdout stream. See
+// register_console_log_sink for why that distinction matters.
+void console_log_callback(int /* level */, const char* message)
+{
+  if (g_log_sink_class == nullptr || g_log_sink_method == nullptr) { return; }
+
+  bool detach = false;
+  JNIEnv* env = get_callback_env(detach);
+  if (env == nullptr) { return; }
+
+  jstring line = env->NewStringUTF(message);
+  if (line != nullptr) {
+    env->CallStaticVoidMethod(g_log_sink_class, g_log_sink_method, line);
+    // A logging call is not the place to raise a Java exception; drop it rather than leave it
+    // pending for whatever JNI call happens to run next on this thread.
+    if (env->ExceptionCheck() == JNI_TRUE) { env->ExceptionClear(); }
+    env->DeleteLocalRef(line);
+  }
+
+  if (detach) { g_jvm->DetachCurrentThread(); }
+}
+
+// Registers console_log_callback with the native logger, once. Done lazily on first use (rather
+// than in JNI_OnLoad) because FindClass needs the caller's classloader, which JNI_OnLoad does not
+// reliably have.
+void register_console_log_sink(JNIEnv* env)
+{
+  std::call_once(g_log_sink_once, [env]() {
+    jclass local_cls = env->FindClass("com/nvidia/cuopt/mathematicaloptimization/NativeLogSink");
+    if (local_cls == nullptr) {
+      env->ExceptionClear();
+      return;
+    }
+    jmethodID method = env->GetStaticMethodID(local_cls, "onLogLine", "(Ljava/lang/String;)V");
+    if (method == nullptr) {
+      env->ExceptionClear();
+      env->DeleteLocalRef(local_cls);
+      return;
+    }
+    g_log_sink_class  = static_cast<jclass>(env->NewGlobalRef(local_cls));
+    g_log_sink_method = method;
+    env->DeleteLocalRef(local_cls);
+    cuopt::set_console_log_callback(&console_log_callback);
+  });
+}
+
 }  // namespace
 
 extern "C" jint JNI_OnLoad(JavaVM* vm, void*)
@@ -421,6 +473,7 @@ Java_com_nvidia_cuopt_mathematicaloptimization_NativeCuOpt_readProblemWithFormat
 extern "C" JNIEXPORT jlong JNICALL
 Java_com_nvidia_cuopt_mathematicaloptimization_NativeCuOpt_createSolverSettings(JNIEnv* env, jclass)
 {
+  register_console_log_sink(env);
   cuOptSolverSettings settings = nullptr;
   if (!check_status(env, cuOptCreateSolverSettings(&settings), "cuOptCreateSolverSettings")) {
     return 0;