将STL与Alchemy一起使用

Question

虽然Alchemy支持编译C++,但使用STL似乎很麻烦,主要是因为std :: string存在问题.奇怪的是Alchemy似乎正在使用GNU libstd ++ v3.4.6.很难相信std :: string在GNU的STL中被破坏了.

有没有人想出这个问题的解决方法？没有STL的C++就像没有水的鱼.

Answer 1

问题不在STL中.GNU的执行std::string引用计数,使用线程安全功能__gnu_cxx::__exchange_and_add和__gnu_cxx::__atomic_add.问题是__exchange_and_add/ __atomic_add被打破了.

解决方案是通过良好实现这些功能来重建STL.

幸运的是,Alchemy发行版为我们留下了一些面包屑.看$ALCHEMY_HOME/avm2-libc/README,它告诉我们如何做到这一点:

The sources used to build avm2-libstdc++.l.bc can be downloaded here:
  http://download.macromedia.com/pub/labs/alchemy/alchemy_gnucpp3-4library_121008.zip

To build avm2-libstdc++.l.bc:
 cd $ALCHEMY_HOME/avm2-libc
 unzip alchemy_gnucpp3-4library_121008.zip
 mv lib/avm2-libstdc++.l.bc lib/avm2-libstdc++.l.bc.OLD
 make 

You should *not* run achacks prior to using these building this library with make.
The Makefiles provided have been preconfigured to use LLVM directly where needed.

通常我希望在libstd ++($ALCHEMY_HOME/avm2-libc/lib/avm2-libstdc++.l.bc)中找到__exchange_and_add/__ atomic_add的实现,但由于某种原因,它们是在libc($ALCHEMY_HOME/avm2-libc/lib/avm2-libc.l.bc)中定义的.

我不确定为什么会出现这种情况,但是我们可以通过破解原子性来解决原型问题.请注意,在解压缩alchemy_gnucpp3-4library_121008.zip之后,您需要编辑两个 atomicity.h文件:

• $ALCHEMY_HOME/avm2-libc/include/c++/3.4/bits/atomicity.h
• $ALCHEMY_HOME/avm2-libc/libstdc++/include/bits/atomicity.h

这是代码:

  /*
   * __exchange_and_add and __atomic_add are broken in Alchemy's libc.
   * Replace them with functioning implementations.  This isn't
   * cross-platform, but this codebase is only compiling for Alchemy anyway.
   */
  #define __exchange_and_add(x,y) __exchange_and_add_fix((x),(y))
  #define __atomic_add(x,y) __exchange_and_add_fix((x),(y))

  /*
   * Correctly implement __exchange_and_add.  It's not thread-safe,
   * but Alchemy isn't threaded, so we should be ok.
   */
  inline _Atomic_word __exchange_and_add_fix(volatile _Atomic_word* __mem, int __val) {
     int orig= *__mem;
     (*__mem)+= __val;
     return orig;
  }

这是一些运行的测试代码,以确保重建的STL工作:

#include <cstdio>
#include <string>
#include <map>
#include <fstream>
using namespace std;

void string_test() {
    string s1;
    string s2;

    s1 = "a";
    s2 = s1; // copy constructor
    s1 = "b";

    // use your favorite TRACE function here
    printf("s1= %s \n", s1.c_str()); // expected: "b", actual: "b"
    printf("s2= %s \n", s2.c_str()); // expected: "a", actual: "b", ERROR
}

void map_test() {
    map<string, int> test_map;

    test_map["test1"]= 1;    
    test_map["test2"]= 2;
    test_map["test3"]= 3;    

    string tmp= "test1";
    printf("%s : %d \n", tmp.c_str(), test_map[tmp]);
}

void ifstream_test()
{
    std::ifstream in("test.txt");

    // ERROR 1:
    // Trying to seek file throws an error:
    // Error #1006: value is not a function.
    // at: basic_filebuf::char_traits::seekoff
    in.seekg(0, std::ios::end);
    int length = in.tellg();
    in.seekg(0, std::ios::beg);
    printf("File Length: %d \n", length);

    while(in.good()) {
        char buffer[512];

        // ERROR 2:
        // RangeError: Error #1125: The index 1092156 is out of range 721.
        // at basic_filebuf::char_traits::underflow::work()
        in.getline(buffer, 512, '\n');

        printf("buffer= %s \n", buffer);
    }
}

int main() {
    string_test();
    map_test();
    ifstream_test();

    return 0;
}

请注意,重建的STL似乎解决了map和ifstream的一些相关问题.