网站开发与支付宝端口连接,网站后缀cc,网络营销推广外包平台,wordpress地址 站点地址转自#xff1a;http://blog.csdn.net/sunny04/article/details/46805261 版权声明#xff1a;本文为博主原创文章#xff0c;未经博主允许不得转载。 进程是操作系统的最小资源管理单元#xff0c; 线程是操作系统最小的执行单元。 一个进程可以有多个线程#xff0c; 也… 转自http://blog.csdn.net/sunny04/article/details/46805261 版权声明本文为博主原创文章未经博主允许不得转载。 进程是操作系统的最小资源管理单元 线程是操作系统最小的执行单元。 一个进程可以有多个线程 也就是说多个线程分享进程的资源包括栈区堆区代码区数据区等。 [cpp] view plaincopy sundhlinhaoIPTV:~$ ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 31675 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) 31675 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited 32bit x86机器上面执行ulimit -a的命令 可以看到 stack size (kbytes, -s) 8192 这是否说明在线程中可以分配8M的局部变量或者说分配7M的局部变量还有1M的空间存储其他的局部变量或者寄存器状态信息例如bp等或者函数压栈信息等 写代码验证如下 [cpp] view plaincopy //test2.cpp #include iostream #include string.h #include pthread.h #include stdio.h using namespace std; void* func(void*a) { cout enter func endl; cout enter func endl; int b[1024*1024*2] {0}; } int main() { int a[1024*1024*3/2]{0}; pthread_t pthread ; pthread_create(pthread, NULL, func, NULL); cout This is a test endl; //pthread_join(pthread, NULL); return 0; } g -g -o test2 test2.cpp -lpthread sundhlinux:~$ gdb test2 GNU gdb (GDB) 7.5-ubuntu Copyright (C) 2012 Free Software Foundation, Inc. License GPLv3: GNU GPL version 3 or later http://gnu.org/licenses/gpl.html This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type show copying and show warranty for details. This GDB was configured as i686-linux-gnu. For bug reporting instructions, please see: http://www.gnu.org/software/gdb/bugs/... Reading symbols from /home/sundh/test2...done. (gdb) r Starting program: /home/sundh/test2 [Thread debugging using libthread_db enabled] Using host libthread_db library /lib/i386-linux-gnu/libthread_db.so.1. [New Thread 0xb7cc1b40 (LWP 10313)] Program received signal SIGSEGV, Segmentation fault. [Switching to Thread 0xb7cc1b40 (LWP 10313)] func (a0x0) at test2.cpp:10 10 cout enter func endl; (gdb) GDB调试结果如上。 main() 函数中分配1.5M的局部变量是不会报错的 但子线程中分配2M的局部变量就会coredump。 可见只能分配不大于2M的局部变量但ulimit -a 查询到的stack size 为8M。 猜想 线程只能分配不大于 1/4 大小的 stack size 给 局部变量 这应该是操作系统的规定。没在网络上面找到相关的文档说明 那我们现在开始验证我们的猜想 通过 ulimit -s命令修改默认的栈大小 下面程序分配5M的局部变量 也就是说线程栈的大小要 20M(5M*4) [cpp] view plaincopy //test1.cpp #include iostream #include string.h #include pthread.h #include stdio.h using namespace std; void* func(void*a) { cout enter func endl; cout enter func endl; int b[1024*1024*5] {0}; } int main() { int a[1024*1024*5]{0}; pthread_t pthread ; pthread_create(pthread, NULL, func, NULL); cout This is a test endl; //pthread_join(pthread, NULL); return 0; } ulimit -s 21504 (也就是21M) , 把默认的stack size设置为21M sundhlinux:~ulimit−s21504sundhlinux: ulimit−s21504sundhlinux: g -g -o test2 test2.cpp -lpthread sundhlinux:~$ ./test2 This is a testenter func enter func 可以成功运行 验证了我们的猜想。 ulimit -s 修改 stack size 也可以通过 pthread_attr_setstacksize() 来修改。 使用ulimit的一个后果就是它会影响到同一环境同一shell或者终端下后续启动的所有程序如果修改成启动时设置的话就会影响到整个系统。 所以大部分情况下还是使用pthread_attr_setstacksize() 代码如下 [cpp] view plaincopy #include pthread.h #include string.h #include stdio.h #include stdlib.h #include unistd.h #include errno.h #include ctype.h #define handle_error_en(en, msg) \ do { errno en; perror(msg); exit(EXIT_FAILURE); } while (0) #define handle_error(msg) \ do { perror(msg); exit(EXIT_FAILURE); } while (0) struct thread_info { /* Used as argument to thread_start() */ pthread_t thread_id; /* ID returned by pthread_create() */ int thread_num; /* Application-defined thread # */ char *argv_string; /* From command-line argument */ }; /* Thread start function: display address near top of our stack, and return upper-cased copy of argv_string */ static void * thread_start(void *arg) { struct thread_info *tinfo arg; char *uargv, *p; span stylecolor:#FF0000;int a[1024*1024*5] {0};/span printf(Thread %d: top of stack near %p; argv_string%s\n, tinfo-thread_num, p, tinfo-argv_string); uargv strdup(tinfo-argv_string); if (uargv NULL) handle_error(strdup); for (p uargv; *p ! \0; p) *p toupper(*p); return uargv; } int main(int argc, char *argv[]) { int s, tnum, opt, num_threads; struct thread_info *tinfo; pthread_attr_t attr; int stack_size; void *res; /* The -s option specifies a stack size for our threads */ stack_size -1; while ((opt getopt(argc, argv, s:)) ! -1) { switch (opt) { case s: stack_size strtoul(optarg, NULL, 0); break; default: fprintf(stderr, Usage: %s [-s stack-size] arg...\n, argv[0]); exit(EXIT_FAILURE); } } num_threads argc - optind; /* Initialize thread creation attributes */ s pthread_attr_init(attr); if (s ! 0) handle_error_en(s, pthread_attr_init); if (stack_size 0) { s span stylecolor:#FF0000;pthread_attr_setstacksize/span(attr, stack_size); if (s ! 0) handle_error_en(s, pthread_attr_setstacksize); } /* Allocate memory for pthread_create() arguments */ tinfo calloc(num_threads, sizeof(struct thread_info)); if (tinfo NULL) handle_error(calloc); /* Create one thread for each command-line argument */ for (tnum 0; tnum num_threads; tnum) { tinfo[tnum].thread_num tnum 1; tinfo[tnum].argv_string argv[optind tnum]; /* The pthread_create() call stores the thread ID into corresponding element of tinfo[] */ s pthread_create(tinfo[tnum].thread_id, attr, thread_start, tinfo[tnum]); if (s ! 0) handle_error_en(s, pthread_create); } /* Destroy the thread attributes object, since it is no longer needed */ s pthread_attr_destroy(attr); if (s ! 0) handle_error_en(s, pthread_attr_destroy); /* Now join with each thread, and display its returned value */ for (tnum 0; tnum num_threads; tnum) { s pthread_join(tinfo[tnum].thread_id, res); if (s ! 0) handle_error_en(s, pthread_join); printf(Joined with thread %d; returned value was %s\n, tinfo[tnum].thread_num, (char *) res); free(res); /* Free memory allocated by thread */ } free(tinfo); exit(EXIT_SUCCESS); } $ ./a.out -s 0x1600000 hola salut servus (0x1500000 20M0x160000021M Thread 1: top of stack near 0xb7d723b8; argv_stringhola Thread 2: top of stack near 0xb7c713b8; argv_stringsalut Thread 3: top of stack near 0xb7b703b8; argv_stringservus Joined with thread 1; returned value was HOLA Joined with thread 2; returned value was SALUT Joined with thread 3; returned value was SERVUS 程序可以正常运行。 这里需要注意的一点是主线程还是使用系统默认的stack size也即8M 不能在main() 里面声明超过2M的局部变量创建子线程的时候调用了pthread_attr_setstacksize(), 修改stack size为21M然后就能在子线程中声明5M的局部变量了。 本文转自张昺华-sky博客园博客原文链接http://www.cnblogs.com/sky-heaven/p/7654950.html如需转载请自行联系原作者