c

问题 Why doesn't the recv system call just block until all the data is received? Every time I have seen a recv call, it's in a while loop which just keeps on calling recv until all the data is there. Why not just have recv block in the first place? 回答1: You can request that recv block until all data is received, with the MSG_WAITALL flag. However, if a signal arrives, a system call that has performed some work (ie, receiving part of the data) cannot be automatically restarted to receive the rest.

问题 Why doesn't the recv system call just block until all the data is received? Every time I have seen a recv call, it's in a while loop which just keeps on calling recv until all the data is there. Why not just have recv block in the first place? 回答1: You can request that recv block until all data is received, with the MSG_WAITALL flag. However, if a signal arrives, a system call that has performed some work (ie, receiving part of the data) cannot be automatically restarted to receive the rest.

问题 I am working on a multithreaded system where a file can be shared among different threads based on the file access permissions . How can I check if file is already opened by another thread. Thanks in advance 回答1: To find out if a named file is already opened on linux, you can scan the /proc/self/fd directory to see if the file is associated with a file descriptor. The program below sketches out a solution: DIR *d = opendir("/proc/self/fd"); if (d) { struct dirent *entry; struct dirent *result

问题 I am working on a multithreaded system where a file can be shared among different threads based on the file access permissions . How can I check if file is already opened by another thread. Thanks in advance 回答1: To find out if a named file is already opened on linux, you can scan the /proc/self/fd directory to see if the file is associated with a file descriptor. The program below sketches out a solution: DIR *d = opendir("/proc/self/fd"); if (d) { struct dirent *entry; struct dirent *result

问题 In C++ and Beyond 2012: Herb Sutter - atomic<> Weapons, 2 of 2 Herb Sutter argues (around 0:38:20) that one should use xchg , not mov / mfence to implement atomic_store on x86. He also seems to suggest that this particular instruction sequence is what everyone agreed one. However, GCC uses the latter. Why does GCC use this particular implementation? 回答1: Quite simply, the mov and mfence method is faster as it does not trigger a redundant memory read like the xchg which will take time. The x86

问题 I am writing a C code to find the middle of linked list. I understood the logic but was unable to figure out how pointers are being used. What is the difference in the way Node *head and Node** head_ref work? void middle(struct Node *head) ; void push(struct Node** head_ref, int new_data) ; 回答1: In the first function header, *head is a pointer to a node object which is allocated somewhere in memory: void middle(struct Node *head); _____________________ | | *head --> | Node object | | [val=1][

问题 In following kernel module, I hooked syscall sys_open, and now trying to send filename to process in userspace using Netlink socket, in response process will return a msg, and then according to msg, the kernel module will proceed further. source code: foo.c #include <linux/module.h> #include <linux/init.h> #include <linux/types.h> #include <asm/uaccess.h> #include <asm/cacheflush.h> #include <linux/syscalls.h> #include <linux/delay.h> // loops_per_jiffy //===============netlink===============

问题 In following kernel module, I hooked syscall sys_open, and now trying to send filename to process in userspace using Netlink socket, in response process will return a msg, and then according to msg, the kernel module will proceed further. source code: foo.c #include <linux/module.h> #include <linux/init.h> #include <linux/types.h> #include <asm/uaccess.h> #include <asm/cacheflush.h> #include <linux/syscalls.h> #include <linux/delay.h> // loops_per_jiffy //===============netlink===============

问题 In following kernel module, I hooked syscall sys_open, and now trying to send filename to process in userspace using Netlink socket, in response process will return a msg, and then according to msg, the kernel module will proceed further. source code: foo.c #include <linux/module.h> #include <linux/init.h> #include <linux/types.h> #include <asm/uaccess.h> #include <asm/cacheflush.h> #include <linux/syscalls.h> #include <linux/delay.h> // loops_per_jiffy //===============netlink===============

问题 In C and C++, the modf function can break floating number into fractional and integral parts. I'm curious about what does "modf" stand for. What is it shorthand for? 回答1: what is modf() shorthand for? The function breaks a floating point number up into whole number and fractional parts. Looking at the 1989 definition (I do not find it in K & R 1st Ed.)... The modf function break the argument value into integral and fractional parts, each of which has the same sign as the argument. It stores