C language programming in Linux: creation and use of threads

The following functions are used to create a thread: includeintpthread_create (pthread_t * thread, pthread_attr_t * attr, void * (* start_routine) (void *), v

The following functions are used to create threads.

1. # Include int pthread_create (pthread_t * thread, pthread_attr_t * attr, void * (* start_routine) (void *), void * arg); void pthread_exit (void * retval ); int pthread_join (pthread * thread, void ** thread_return );

Pthread_create creates a thread. thread is used to indicate the ID of the thread to be created. attr indicates the attributes of the thread during creation. We use NULL to indicate that the default attribute is used. Start_routine function pointer is the function that starts execution after the thread is created successfully. arg is the only parameter of this function. Indicates the parameter passed to start_routine.

The pthread_exit function is similar to the exit function used to exit the thread. this function ends the thread, releases the function resources, and blocks the thread until other threads use the pthread_join function to wait for it. Then pass the * retval value to ** thread_return. because this function releases function resources, retval cannot point to the local variable of the function.

Pthread_join is the same as wait call to wait for the specified thread. Next we will use an instance to explain how to use it. In practice, we often need to back up some files. The following program backs up all files in the current directory. the suffix after backup is bak.

1. # Include # define BUFFER 512 struct copy_file {int infile; int outfile ;}; void * copy (void * arg) {int infile, outfile; int bytes_read, bytes_write, * bytes_copy_p; char buffer [BUFFER], * buffer_p; struct copy_file * file = (struct copy_file *) arg; infile = file-> infile; outfile = file-> outfile;/* when the thread exits, all variable spaces are released, so I We had to allocate our own memory */if (bytes_copy_p = (int *) malloc (sizeof (int) = NULL) pthread_exit (NULL); bytes_read = bytes_write = 0; * bytes_copy_p = 0; while (bytes_read = read (infile, buffer, BUFFER ))! = 0) {if (bytes_read =-1) & (errno! = EINTR) break; else if (bytes_read> 0) {buffer_p = buffer; while (bytes_write = write (outfile, buffer_p, bytes_read ))! = 0) {if (bytes_write =-1) & (errno! = EINTR) break; else if (bytes_write = bytes_read) break; else if (bytes_write> 0) {buffer_p + = bytes_write; bytes_read-= bytes_write ;}} if (bytes_write =-1) break; * bytes_copy_p + = bytes_read;} close (infile); close (outfile); pthread_exit (bytes_copy_p);} int main (int argc, char ** argv) {pthread_t * thread; struct copy_file * file; int byte_copy, * byte_copy_p, num, I, j; char filename [BUFFER]; struct dirent ** n Amelist; struct stat filestat;/* obtain the number of all files (including directories) in the current path */if (num = scandir (". ", & namelist, 0, alphasort) <0) {fprintf (stderr," Get File Num Error: % sna ", strerror (errno); exit (1 );} /* allocate space to the thread. In fact, there is no need for so many */if (thread = (pthread_t *) malloc (sizeof (pthread_t) * num) = NULL) | (file = (struct copy_file *) malloc (sizeof (struct copy_file) * num) = NULL) {fprintf (stderr, "Out Of Memory! Na "); exit (1) ;}for (I = 0, j = 0; id_name); if (stat (filename, & filestat) =-1) {fprintf (stderr, "Get File Information: % sna", strerror (errno); exit (1) ;}/ * we ignore the directory */if (! S_ISREG (filestat. st_mode) continue; if (file [j]. infile = open (filename, O_RDONLY) <0) {fprintf (stderr, "Open % s Error: % sna", filename, strerror (errno); continue ;} strcat (filename ,". bak "); if (file [j]. outfile = open (filename, O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR) <0) {fprintf (stderr, "Creat % s Error: % sna", filename, strerror (errno); continue;}/* create thread to copy files */if (pthread_create (& thread [j], NULL, copy, (void *) & File [j])! = 0) fprintf (stderr, "Create Thread [% d] Error: % sna", I, strerror (errno); j ++;} byte_copy = 0; for (I = 0; I