This can lead to false positives due to missed synchronization. Unlike functions marked with nosanitize ('thread') attribute, ignored functions are not instrumented at all. ThreadSanitizer supports src and fun entity types in Sanitizer special case list, that can be used to suppress data race reports in the specified source files or functions.
It is implemented with a pthread.h header and a thread library. Cpp - Wall - std = c ++ 11 - O3 - static - pthread \pthreads defines a set of C programming language types, functions and constants. This here will work: g ++ - o one one.
Adding -lpthread will only link the pthread library and it will not.When you use -pthread, the compiler will already link against pthread (and depending on the platform, it does define extra macros like -D_REENTRANT, see this question for more details).So if -pthread implies -lpthread, why do you need you specify -lpthread when you are linking statically? And what does Wl,-whole-archive do? Understanding weak symbolsOn Unix, the ELF file format is used, which has the concept of weak and strong symbols. - Wl ,- whole - archive - lpthread - Wl ,- no - whole - archiveWorking Solution for Undefined reference to pthreadcreate error in C Linux. Mutexes Condition variables Synchronization between threads using read/write locks and.
For details, refer to this question about the usage of weak symbols in glibc. On the other hand, if no multi-threading library is linked, the executable will use the stubs for the synchronization function.Glibc (providing fputc) and pthreads seem to use exactly this trick. When linking the multi-threading library, the linker can then replace the stubs by the real synchronization functions (defined as strong symbols and implemented by the threading-library). An implementation could therefore implement the synchronization functions as empty stubs, and declare the functions as weak symbols.Later, if a multi-threading library is linked (e.g., pthread), it becomes obvious that single-thread support is not intended. In a single-threaded environment, you do not want to pay the costs. Another is to use stubs, which can later to replaced if necessary.For example, fputc (conceptionally used by printf) is required by POSIX to be thread-safe and needs to be synchronized, which is costly.
Linking Pthread C Full Back To
O : 00000000000006a0 T _pthread_mutex_lock0000000000000000 t _pthread_mutex_lock_full Back to the example programBy looking at the shared library dependencies of the dynamically linked executable, I get almost the same output of ldd on my machine: $ ldd oneLinux - vdso. A 2 > /dev/ null | grep pthread_mutex_lockPthread_mutex_lock. The statically linked pthread library contains it as a strong symbol: $ nm / usr / lib / libpthread. A 2 > /dev/ null | grep pthread_mutex_lock"w" stands for "weak", so the statically linked libc library contains _pthread_mutex_lock as a weak symbol.
0 => / usr / lib / libpthread. 1 ( 0x00007fcaae983000 )Libpthread. 1 => / usr / lib / libgcc_s. 6 ( 0x00007fcaaeb9b000 )Libgcc_s. 6 ( 0x00007fcaaeeb3000 )Libm. 6 => / usr / lib / libstdc ++.
0 | grep pthread_joinIn the dynamically linked executable, the linker will replace weak symbols by strong symbols. 6 | grep pthread_join$ nm / usr / lib / libpthread. That symbol can be found in the (dynamically linked) libraries listed in the ldd ouput, namely in libstdc++.so.6 and libpthread.so.0: $ nm / usr / lib / libstdc ++. / oneStd :: ios_base :: Init :: Init ()( 0x563ab8df71b1 , 0x7ffdc483cae8 , 0x7ffdc483caf8 , 160 ) = 0_cxa_atexit ( 0x7fab3023bc20 , 0x563ab8df71b1 , 0x563ab8df7090 , 6 ) = 0 operator new ( unsigned long )( 16 , 0x7ffdc483cae8 , 0x7ffdc483caf8 , 192 ) = 0x563ab918bc20Std :: thread :: _M_start_thread ( std :: unique_ptr >, void (*)())( 0x7ffdc483c990 , 0x7ffdc483c998 , 0x7fab2fa52320 , 0x7fab2fa43a80 ) = 0 operator new ( unsigned long )( 16 , 0x7fab2f6a1fb0 , 0 , 0x800000 ) = 0x563ab918bd70Std :: thread :: _M_start_thread ( std :: unique_ptr >, void (*)())( 0x7ffdc483c990 , 0x7ffdc483c998 , 0x7fab2fa52320 , 0x7fab2fa43a80 ) = 0 operator new ( unsigned long )( 16 , 0x7fab2eea0fb0 , 0 , 0x800000 ) = 0x563ab918bec0Std :: thread :: _M_start_thread ( std :: unique_ptr >, void (*)())( 0x7ffdc483c990 , 0x7ffdc483c998 , 0x7fab2fa52320 , 0x7fab2fa43a80test start) = 0 operator new ( unsigned long )( 16 , 0x7fab2e69ffb0 , 0 , 0x800000 ) = 0x563ab918c010Std :: thread :: join ()( 0x7ffdc483c9a0 , 0x7fab2de9efb0 , 0 , 0x800000test startStd :: thread :: join ()( 0x7ffdc483c9a8 , 0x7fab2eea19c0 , 0x7fab2f6a2700 , 0 ) = 0Std :: thread :: join ()( 0x7ffdc483c9b0 , 0x7fab2e6a09c0 , 0x7fab2eea1700 , 0 ) = 0Std :: thread :: join ()( 0x7ffdc483c9b8 , 0x7fab2de9f9c0 , 0x7fab2e6a0700 , 0 ) = 0 +++ exited ( status 0 ) +++As an example, std::thread::join is called, which will most likely use pthread_join internally. 2 ( 0x00007fcaaf23b000 )Printing out the library calls with ltrace, leads to the following output: $ ltrace - C. 6 ( 0x00007fcaae3bb000 ) / lib64 / ld - linux - x86 - 64.so.
Linking Pthread C How To Use The
The most extreme example that I have seen and personally struggled with a while to get it working is to link TBB statically. I assume it is because static linking on Linux has become rather an edge case, whereas dynamic linking is often the canonical approach on how to use the libraries (for a comparison, see Static linking vs dynamic linking). At least, I found no clear documentation on that subject. That is why -Wl,-whole-archive -lpthread -Wl,-no-whole-archive is needed.Finding it out is a bit trial-and-error.
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