C++ 未定义的对 `pthread_mutex_trylock' 的引用
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undefined reference to `pthread_mutex_trylock'
提问by enzo1959
I have the following test program.
我有以下测试程序。
#include <iostream>
#include <cstdlib>
using namespace std;
pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
int main(int argc, char *argv[])
{
int iret;
iret = pthread_mutex_trylock( & mymutex );
cout << "Test2 !!! " << endl;
pthread_mutex_unlock( & mymutex );
return EXIT_SUCCESS;
}
If I compile it without adding the pthread library I get the error for unresolved error for pthread_mutex_trylock , but only for function pthread_mutex_trylock.
如果我在不添加 pthread 库的情况下编译它，则会收到 pthread_mutex_trylock 的未解决错误的错误，但仅适用于函数 pthread_mutex_trylock。
If I replace pthread_mutex_trylock with pthread_mutex_trylock the program is compiled and runnig well also without the -lpthread* option.
如果我用 pthread_mutex_trylock 替换 pthread_mutex_trylock，则程序也可以在没有 -lpthread* 选项的情况下编译并运行良好。
If I add the -lpthraed option to the compile commands all runs well this run well : $ g++ test2.c -o test2 -lpthreadthis warn unresolved : $ g++ test2.c -o test2
如果我将 -lpthraed 选项添加到编译命令中，则所有运行良好： $ g++ test2.c -o test2 -lpthread此警告未解决： $ g++ test2.c -o test2
Example error output:
$ g++ test2.c -o test2
/tmp/ccU1bBdU.o: In function main':
test2.c:(.text+0x11): undefined reference topthread_mutex_trylock'
collect2: ld returned 1 exit status
示例错误输出：$ g++ test2.c -o test2 /tmp/ccU1bBdU.o: In function main':
test2.c:(.text+0x11): undefined reference topthread_mutex_trylock' collect2: ld returns 1 exit status
If I replace the instruction iret = pthread_mutex_trylock( & mymutex );
如果我替换指令iret = pthread_mutex_trylock( & mymutex );
with iret = pthread_mutex_lock( & mymutex );the program compiles and run without error also if didn't add the pthread libarry to the compile command I know that is right to have the unresolved error if I didn't use the -lpthread option , but why I have not the same unresolved error also for other pthread_ function ?
与iret = pthread_mutex_lock( & mymutex ); 如果没有将 pthread 库添加到编译命令中，程序编译和运行也不会出错也适用于其他 pthread_ 函数？
I'm using gcc 4.4.2 on fedora 12
我在 Fedora 12 上使用 gcc 4.4.2
$ g++ --version
g++ (GCC) 4.4.2 20091222 (Red Hat 4.4.2-20)
Copyright (C) 2009 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Do some have some suggestion about the meaning of this unreference only for pthread_mutex_trylock ?
有些人对 pthread_mutex_trylock 的这种未引用的含义有什么建议吗？
thanks for the help, Enzo
感谢您的帮助，恩佐
回答by P Shved
If you use pthread functions you should link your object files with -lpthreadand not worry about whether symbols are included in libc.
如果您使用的并行线程功能，你应该用你的链接对象文件-lpthread，而不用担心符号是否被包括在libc。
The rationale behind this is saidto be such: some time ago the stubs in libc were used when application that used threads was run on a system without threading support. On such system, pthread_*functions became linked to libcstubs that returned errors showing that there's no threading functionality. While on "threaded" systems they were linked to pthreadlibrary and worked correctly.
据说这背后的基本原理是这样的：前一段时间，当使用线程的应用程序在没有线程支持的系统上运行时，会使用 libc 中的存根。在这样的系统上，pthread_*函数链接到libc存根，存根返回错误，表明没有线程功能。在“线程”系统上，它们链接到pthread库并正常工作。
Obviously, pthread_mutex_trylockfunction appeared after the policy changed to linking with -lpthread. So there's no stub for it.
显然，pthread_mutex_trylock函数出现在策略改为与 连接后-lpthread。所以没有存根。
回答by Chris Jester-Young
You should perform both the compilation and linkage with the -pthreadoption, to be portable. On some systems, the compilation will have specific flags added (e.g., -D_REENTRANT) with -pthreadspecified.
您应该使用-pthread选项执行编译和链接，以便可移植。在某些系统上，编译将添加（例如，-D_REENTRANT）-pthread指定的特定标志。
If you're curious to see what -pthreadwill do to your compile and link flags, run gcc -dumpspecs.
如果您想知道-pthread对编译和链接标志有何影响，请运行gcc -dumpspecs.
