Avoid deadlocks after fork

score/launch_manager/src/daemon/src/common/BUILD

@@ -50,6 +50,14 @@ cc_library(
     }),
 )
 
+cc_library(
+    name = "signal_safe_log",
+    hdrs = ["signal_safe_log.hpp"],
+    include_prefix = "score/mw/launch_manager/common",
+    strip_include_prefix = "/score/launch_manager/src/daemon/src/common",
+    visibility = ["//score/launch_manager/src/daemon:__subpackages__"],
+)
+
 cc_library(
     name = "constants",
     hdrs = ["constants.hpp"],

score/launch_manager/src/daemon/src/common/signal_safe_log.hpp

@@ -0,0 +1,125 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ********************************************************************************/
+
+#include <charconv>
+#include <unistd.h>
+#include <array>
+#include <cstdlib>
+#include <string_view>
+
+#ifndef SIGNAL_SAFE_LOG_HPP_INCLUDED
+#define SIGNAL_SAFE_LOG_HPP_INCLUDED
+
+namespace
+{
+
+/// @brief Utility for building log messages in an async signal safe context.
+template <int C>
+class signal_safe_buffer
+{
+  public:
+    std::array<char, C> buffer = {};
+    size_t start = 0;
+    size_t end = 0;
+
+    /// @brief Append the given string to the buffer.
+    template <typename T, std::enable_if_t<std::is_convertible_v<T, std::string_view>, bool> = true>
+    void append(const T& value)
+    {
+        const auto string = std::string_view(value);
+
+        size_t length = std::min(string.length(), buffer.size() - end);
+
+        for (size_t index = 0; index < length; ++index)
+        {
+            buffer[end++] = string[index];
+        }
+    }
+
+    /// @brief Append the given integer to the buffer.
+    template <typename T, std::enable_if_t<std::is_integral_v<T>, bool> = true>
+    void append(const T& value)
+    {
+        const auto [pointer, error] = std::to_chars(&buffer[end], &buffer.back(), value);
+
+        if (error == std::errc{})
+        {
+            end = pointer - &buffer.front();
+        }
+    }
+
+    /// @brief Write out the buffer to standard error.
+    /// @return Whether the write succeeded. True means the whole message was
+    ///         written. False means nothing, or only part was written.
+    [[nodiscard]] bool flush()
+    {
+        while (start < end)
+        {
+            const auto written = write(STDERR_FILENO, &buffer[start], end - start);
+
+            if (written >= 0)
+            {
+                start += written;
+            }
+            else if (errno != EINTR)
+            {
+                return false;
+            }
+        }
+
+        // Rewind the indices in case the buffer is used again.
+        start = 0;
+        end = 0;
+
+        return true;
+    }
+};
+
+}  // namespace
+
+namespace score::lcm::internal
+{
+
+template <typename... T>
+[[nodiscard]] bool signal_safe_log(const T&... values)
+{
+    const int original_errno = errno;  // For reentrancy
+
+    signal_safe_buffer<1024> buffer = {};
+    (buffer.append(values), ...);
+    buffer.append("\n");
+    const bool written = buffer.flush();
+
+    errno = original_errno;  // For reentrancy
+
+    return written;
+}
+
+template <typename... T>
+[[nodiscard]] bool signal_safe_log_errno(int log_errno, const T&... values)
+{
+#if _GNU_SOURCE && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 32
+    // strerrordesc_np is documented as async signal safe.
+    return signal_safe_log(values..., " (", strerrordesc_np(log_errno), ")");
+#elif __QNXNTO__
+    // QNX strerror is documented as async signal safe.
+    return signal_safe_log(values..., " (", strerror(log_errno), ")");
+#else
+    // POSIX strerror is not async signal safe. Log the raw number instead.
+    return signal_safe_log(values..., " (errno ", log_errno, ")");
+#endif
+}
+
+}  // namespace score::lcm::internal
+
+#endif

score/launch_manager/src/daemon/src/process_group_manager/details/BUILD

@@ -109,6 +109,7 @@ cc_library(
     visibility = ["//score/launch_manager/src/daemon/src/process_group_manager:__pkg__"],
     deps = [
         "//score/launch_manager/src/daemon/src/common:log",
+        "//score/launch_manager/src/daemon/src/common:signal_safe_log",
         "//score/launch_manager/src/daemon/src/control:control_client_channel",
         "//score/launch_manager/src/daemon/src/osal:ipc_comms",
         "//score/launch_manager/src/daemon/src/osal:security_policy",