mutil_thread append string cause core

Question

i use multi thread to update each item(string) of global vector each thread update item(string) with different index i think is a good way to avoid updating same data but i still get core, i do not know why

extern vector<string> gTestVec; #define NUM 10 void * worker(void * args) { thread_data * p = (thread_data *)args; int i = p->thread_id; for (int j=0; j<100; j++) { gTestVec[i] += "a"; } return NULL; } void do_complete_stage_test::excute() { int i = 0; pthread_t thd[NUM]; thread_data data[NUM]; for (i=0; i<NUM; i++) { gTestVec.push_back(format("%d", i)); data[i].thread_id = i; if (0 != pthread_create(&(thd[i]), NULL, &worker, (void *)&data[i])) { printf("pthread_create failed"); } } for (int i=0; i<NUM; i++) { if (0 != pthread_join(thd[i], NULL)) { printf("pthread_join failed"); } } }

when i run the code,sometimes get coredump

Starting program: /data/settle_script/isp_tran_collect/bin/isp_tran_collect -p 2134234 [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib64/libthread_db.so.1". [New Thread 0x7ffff2623700 (LWP 6316)] [New Thread 0x7fffefb0e700 (LWP 6317)] [New Thread 0x7fffef30d700 (LWP 6318)] Program received signal SIGSEGV, Segmentation fault. [Switching to Thread 0x7fffef30d700 (LWP 6318)] 0x00007ffff6787d67 in ?? () from /lib64/libstdc++.so.6 (gdb) bt #0 0x00007ffff6787d67 in ?? () from /lib64/libstdc++.so.6 #1 0x00007ffff678899b in std::string::reserve(unsigned long) () from /lib64/libstdc++.so.6 #2 0x00007ffff6788bbf in std::string::append(char const*, unsigned long) () from /lib64/libstdc++.so.6 #3 0x000000000044babe in append (__s=0x880492 "a", this=<optimized out>) at /usr/include/c++/4.8.2/bits/basic_string.h:1009 #4 operator+= (__s=0x880492 "a", this=<optimized out>) at /usr/include/c++/4.8.2/bits/basic_string.h:942 #5 worker (args=<optimized out>) at ../src/do_complete_stage_test.cpp:21 #6 0x00007ffff7bc6e25 in start_thread () from /lib64/libpthread.so.0 #7 0x00007ffff5ee635d in clone () from /lib64/libc.so.6

thanks for your help!!!

Why use pthread instead of std::thread? With std::thread you could have a thread logic function with signature void worker(std::string& arg) (std::thread thd[NUM]; for (size_t i = 0; i != NUM; ++i){ ... thd[i] = std::thread(worker, std::reference_wrapper(gTestVec[i])); }) — fabian
– fabian, Commented Jun 6, 2022 at 8:09

PeterT · Accepted Answer · 2022-06-06 08:00:35Z

You are potentially changing the capacity of the vector after you already started some threads.

The easiest way to prevent the vector from re-allocating and moving its contents is to reserve the amount of space before you start the first worker thread.

So call

gTestVec.reserve(NUM);

Before your loop.

Collectives™ on Stack Overflow

mutil_thread append string cause core

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related