Hello everybody.I have an exercise (kiwi engine) in university (OS course) and I have to use thread.
The code is big (10.000 lines) and I only have to use threads to make it faster.
In the following code if you can see a comment like: // <<<<<<<<<<<<<<<
it means that I have added this line(the other lines already exists).
So,as you can see below,I make an array of threads given in command line
If 2nd string is "readwrite" the program runs only this if statement.
So, I create a these threads to call _readwrite(...) function.
The _readwrite_test(...) lock a mutex to call function _write_test(...) ,unlock it and the do the same thing for _read_test(...)
These 2 functions write and read data from a data base
Do not pay attention what these function do.
Anyway,when I run gdb ,I recieve
Thread 2 " kiwi-bench" received signal SIGSEGV, Segmentation fault. [Switching to Thread 0x7ffff78b1700 (LWP 53813 )] __memmove_avx_unaligned_erms () at ../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:306 306 ../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S: No such file or directory.
Do not run the code(nothing will happen).
If I run only read_test or write_test all works fine.I think the problem is in the lock/unlock of mutex.
What can I do?What do you think?
I hope you understand what I want to do.
I need your help!!
Thank you very much.
What I have tried:
struct vars // <<<<<<<<<<<<<<< int r; long int count; double percentage; pthread_mutex_t my_mutex = PTHREAD_MUTEX_INITIALIZER; // <<<<<<<<<<<<<<< void *_readwrite_test( void *arg) // <<<<<<<<<<<<<<< struct vars *my_var = ( struct vars *)arg; int put_percentage = ( int ) ((my_var- > percentage/100) * my_var- > count); // casting to integer int get_percentage = ( int ) (my_var- > count - put_percentage); // casting to integer printf( " @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ put=%d --- get=%d\n" , put_percentage , get_percentage); pthread_mutex_lock(&my_mutex); _write_test(put_percentage , my_var- > r); pthread_mutex_unlock(&my_mutex); pthread_mutex_lock(&my_mutex); _read_test(get_percentage , my_var- > r); pthread_mutex_unlock(&my_mutex); return NULL; int main( int argc, char ** argv) long int count; pthread_t threads[ atoi(argv[ 3 ]) ]; // <<<<<<<<<<<<<<< srand(time(NULL)); if (argc < 4 ) { fprintf(stderr, " Usage: db-bench <write | read | readwrite> <count>\n" ); exit( 1 ); if (strcmp(argv[ 1 ], " write" ) == 0 ) { int r = 0 ; count = atoi(argv[ 2 ]); _print_header(count); _print_environment(); if (argc == 4 ) r = 1 ; _write_test(count, r); } else if (strcmp(argv[ 1 ], " read" ) == 0 ) { int r = 0 ; count = atoi(argv[ 2 ]); _print_header(count); _print_environment(); if (argc == 4 ) r = 1 ; _read_test(count, r); else if (strcmp(argv[ 1 ] , " readwrite" ) == 0 ) // <<<<<<<<<<<<<<< // dhmioyrghsa ena struct gia na perasw 2 parametrous sthn readwrite_test mesw nhmatwn struct vars my_var; my_var.count = atoi(argv[ 2 ]); my_var.r = 0 ; my_var.percentage = atoi(argv[ 4 ]); // percentage of PUT _print_header(my_var.count); _print_environment(); if (argc == 4 ) my_var.r = 1 ; for ( int i = 0 ; i < atoi(argv[ 3 ]); i++) pthread_create(&threads[i] , NULL , _readwrite_test , &my_var); for ( int i = 0 ; i < atoi(argv[ 3 ]); i++) printf( " $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$??????????????????????????????????????????????????????????????????????????????????????? Thread join\n" ); pthread_join(threads[i] , NULL); else { fprintf(stderr, " Usage: db-bench <write | read | readwrite> <count> <random>\n" ); exit( 1 ); return 1 ;

You are passing the same structure to each thread of _readwrite_test , so you probably need to add the lock at the very beginning of the function, and the unlock at the very end. However, you still need to use the debugger to find out exactly where the segv occurs, as there is always the possibility that there is another cause.

SIGSEGV means that you dereferenced an invalid pointer, most often one that was NULL or uninitialized.
EDIT : To follow up, let me start by saying that I haven't used this pthread stuff. But the following looks suspicious:
pthread_mutex_t my_mutex = PTHREAD_MUTEX_INITIALIZER;A mutex needs to be allocated from the kernel, and I think this only initializes my_mutex to a default value, after which you try to lock it. This could be the source of your bad pointer problem. I would suggest looking for a pthread function that appears to allocate a mutex.

Read the question carefully.

Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.

If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.

Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question. Let's work to help developers, not make them feel stupid.