FinallyGuard included by multiple libraries; Leads to linking errors

[jbfitb]

Briefly summarize your issue:

• Compiling for iOS
• Trying to link static libraries into a single executable
• Getting linker errors:

duplicate symbol 'alexaClientSDK::avsCommon::utils::error::FinallyGuard::~FinallyGuard()' in:
    <redacted_path>(AlertScheduler.cpp.o)
    <redacted_path>(LocaleWakeWordsSetting.cpp.o)
duplicate symbol 'alexaClientSDK::avsCommon::utils::error::FinallyGuard::~FinallyGuard()' in:
    <redacted_path>(AlertScheduler.cpp.o)
    <redacted_path>(LocaleWakeWordsSetting.cpp.o)
duplicate symbol 'alexaClientSDK::avsCommon::utils::error::FinallyGuard::FinallyGuard(std::__1::function<void ()> const&)' in:
    <redacted_path>(AlertScheduler.cpp.o)
    <redacted_path>(LocaleWakeWordsSetting.cpp.o)
duplicate symbol 'alexaClientSDK::avsCommon::utils::error::FinallyGuard::FinallyGuard(std::__1::function<void ()> const&)' in:
    <redacted_path>(AlertScheduler.cpp.o)
    <redacted_path>(LocaleWakeWordsSetting.cpp.o)
duplicate symbol 'alexaClientSDK::avsCommon::utils::error::FinallyGuard::~FinallyGuard()' in:
    <redacted_path>(AlertScheduler.cpp.o)
    <redacted_path>(ReportStateHandler.cpp.o)
duplicate symbol 'alexaClientSDK::avsCommon::utils::error::FinallyGuard::~FinallyGuard()' in:
    <redacted_path>(AlertScheduler.cpp.o)
    <redacted_path>(ReportStateHandler.cpp.o)
duplicate symbol 'alexaClientSDK::avsCommon::utils::error::FinallyGuard::FinallyGuard(std::__1::function<void ()> const&)' in:
    <redacted_path>(AlertScheduler.cpp.o)
    <redacted_path>(ReportStateHandler.cpp.o)
duplicate symbol 'alexaClientSDK::avsCommon::utils::error::FinallyGuard::FinallyGuard(std::__1::function<void ()> const&)' in:
    <redacted_path>(AlertScheduler.cpp.o)
    <redacted_path>(ReportStateHandler.cpp.o)
ld: 8 duplicate symbols for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Research into the Issue

• It looks like FinallyGuard has its implementation in its header file
• Before 1.15, FinallyGuard was only used in AlertScheduler.cpp so this wasn't an issue.
• As of 1.15, FinallyGuard is used by three objects: AlertScheduler.cpp.o, LocaleWakeWordsSetting.cpp.o, and ReportStateHandler.cpp.o
• The FinallyGuard symbols are now referenced in libAVSSystem, libAlerts, and libDeviceSettings
• When linking two or more of these three libraries, there are errors due to duplicate symbols.

Possible Solution

It seems that creating a FinallyGuard.cpp and removing the implementation from the header file fixes this issue:

FinallyGuard.h

#ifndef ALEXA_CLIENT_SDK_AVSCOMMON_UTILS_INCLUDE_AVSCOMMON_UTILS_ERROR_FINALLYGUARD_H_
#define ALEXA_CLIENT_SDK_AVSCOMMON_UTILS_INCLUDE_AVSCOMMON_UTILS_ERROR_FINALLYGUARD_H_

#include <functional>

namespace alexaClientSDK {
namespace avsCommon {
namespace utils {
namespace error {

/**
 * Define a class that can be used to run a function when the object goes out of scope.
 *
 * This simulates try-finally statements. The following structure:
 *
 * @code
 * try {
 *   <try_block>
 * } finally {
 *   <finally_block>
 * }
 * @endcode
 *
 * can be replaced by:
 *
 * @code
 *   FinallyGuard guard { []{ <finally_block> }};
 *   <try_block>
 * @endcode
 */
class FinallyGuard {
public:
    /**
     * Constructor.
     *
     * @param finallyFunction The function to be executed when the object goes out of scope.
     */
    FinallyGuard(const std::function<void()>& finallyFunction);

    /**
     * Destructor. Runs @c m_function during destruction.
     */
    ~FinallyGuard();

private:
    /// The function to be run when this object goes out of scope.
    std::function<void()> m_function;
};

}  // namespace error
}  // namespace utils
}  // namespace avsCommon
}  // namespace alexaClientSDK
#endif  // ALEXA_CLIENT_SDK_AVSCOMMON_UTILS_INCLUDE_AVSCOMMON_UTILS_ERROR_FINALLYGUARD_H_

FinallyGuard.cpp

#include "AVSCommon/Utils/Error/FinallyGuard.h"

namespace alexaClientSDK {
namespace avsCommon {
namespace utils {
namespace error {

FinallyGuard::FinallyGuard(const std::function<void()>& finallyFunction) : m_function{finallyFunction} {
}

FinallyGuard::~FinallyGuard() {
    if (m_function) {
        m_function();
    }
}

}  // namespace error
}  // namespace utils
}  // namespace avsCommon
}  // namespace alexaClientSDK

AVSCommon/CMakeLists.txt

+     Utils/src/FinallyGuard.cpp

[scotthea-amazon]

Hello @jbfitb,

This is definitely a bug. Thank you for reporting this issue!

Best regards,
-SWH

[caleighatamazon]

Closing this issue for now. We're tracking the bug internally. Please feel free to re-open the issue if you have more questions or concerns.

[scotthea-amazon]

Hello @jbfitb,

This issue has been fixed in the 1.17 release. Thank you again (and again) for your help!

Best regards,
-SWH