5

在实际代码中使用它之前，我正在std::async隔离测试，以验证它在我的平台（即 ubuntu 12.10 64 位）上是否正常工作。

它有效（很少见）并且通常只是挂起。如果它对你有用，不要妄下结论。多试几次，它可能会挂起。

如果我删除 pthread_mutex 测试，它不会挂起。这是我可以重现挂起的最小代码。是否有某些原因不能将 C pthread 代码与 C++ 异步代码混合使用？

#include <iostream>
#include <pthread.h>
#include <chrono>
#include <future>
#include <iomanip>
#include <sstream>
#include <type_traits>

template<typename T>
std::string format_ns(T &&value)
{
    std::stringstream s;
    if (std::is_floating_point<T>::value)
        s << std::setprecision(3);

    if (value >= 1000000000)
        s << value / 1000000000 << "s";
    else if (value >= 1000000)
        s << value / 1000000 << "ms";
    else if (value >= 1000)
        s << value / 1000 << "us";
    else
        s << value  << "ns";
    return s.str();
}

template<typename F>
void test(const std::string &msg, int iter, F &&lambda)
{
    std::chrono::high_resolution_clock clock;
    auto st = clock.now();

    int i;
    for (i = 0; i < iter; ++i)
        lambda();
    auto en = clock.now();
    std::chrono::nanoseconds dur = std::chrono::duration_cast<
        std::chrono::nanoseconds>(en-st);

    std::cout << msg << format_ns(dur.count() / i) << std::endl;
}

int test_pthread_mutex()
{
    pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;

    test("pthread_mutex_lock/pthread_mutex_unlock: ", 1000000000,
    [&]()
    {
        pthread_mutex_lock(&m);
        pthread_mutex_unlock(&m);
    });

    pthread_mutex_destroy(&m);

    return 0;
}

int test_async()
{
    test("async: ", 100,
    [&]()
    {
        auto asy = std::async(std::launch::async, [](){});
        asy.get();
    });

    return 0;
}

int main()
{
    test_pthread_mutex();
    test_async();
}

这是构建命令行：

g++ -Wextra -Wall  --std=c++11 -pthread mutexperf/main.cpp

没有构建输出消息。

这是 g++ -v 的输出

Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.7.2-2ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs --enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.7 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.7.2 (Ubuntu/Linaro 4.7.2-2ubuntu1)
4

2 回答 2

2

我在几台不同的计算机上进行了尝试，发现它确实像@johan 评论的那样运行良好。我调查了我正在使用的机器，发现硬盘驱动器开始出现故障的证据。它有一些坏扇区，并且dmesg在异常的 4 秒冻结后还报告了几次硬盘“硬重置”。奇怪，在发布问题之前我没有看到任何问题。在编译/链接或加载可执行文件时，这可能是一些微妙/间歇性的损坏。

[44242.380936] ata3.00: exception Emask 0x10 SAct 0x0 SErr 0x800000 action 0x6 frozen
[44242.380942] ata3.00: irq_stat 0x08000000, interface fatal error
[44242.380946] ata3: SError: { LinkSeq }
[44242.380950] sr 2:0:0:0: CDB: 
[44242.380952] Get event status notification: 4a 01 00 00 10 00 00 00 08 00
[44242.380965] ata3.00: cmd a0/00:00:00:08:00/00:00:00:00:00/a0 tag 0 pio 16392 in
[44242.380965]          res 50/00:03:00:08:00/00:00:00:00:00/a0 Emask 0x10 (ATA bus error)
[44242.380968] ata3.00: status: { DRDY }
[44242.380974] ata3: hard resetting link
[44242.700025] ata3: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[44242.704849] ata3.00: configured for UDMA/100
[44242.720055] ata3: EH complete
[44970.117542] ata3.00: exception Emask 0x10 SAct 0x0 SErr 0x800100 action 0x6 frozen
[44970.117547] ata3.00: irq_stat 0x08000000, interface fatal error
[44970.117551] ata3: SError: { UnrecovData LinkSeq }
[44970.117555] sr 2:0:0:0: CDB: 
[44970.117557] Get event status notification: 4a 01 00 00 10 00 00 00 08 00
[44970.117570] ata3.00: cmd a0/00:00:00:08:00/00:00:00:00:00/a0 tag 0 pio 16392 in
[44970.117570]          res 50/00:03:00:08:00/00:00:00:00:00/a0 Emask 0x10 (ATA bus error)
[44970.117573] ata3.00: status: { DRDY }
[44970.117579] ata3: hard resetting link
[44970.436662] ata3: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[44970.443159] ata3.00: configured for UDMA/100
[44970.456639] ata3: EH complete

感谢任何花时间查看我的问题的人！

于 2013-04-07T17:50:05.287 回答
0

您是否尝试复制互斥锁而不是在 lambda 中通过引用传递？

int test_pthread_mutex()
{
    pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;

    test("pthread_mutex_lock/pthread_mutex_unlock: ", 1000000000,
    [=]()
    {
        pthread_mutex_lock(&m);
        pthread_mutex_unlock(&m);
    });

    pthread_mutex_destroy(&m);

    return 0;
}
于 2013-04-07T16:04:51.743 回答