12.7 Exercise: Parallel File Copy

This section develops a parallel file copy as an extension of the copier application of Program 12.8. Be sure to use thread-safe calls in the implementation. The main program takes two command-line arguments that are directory names and copies everything from the first directory into the second directory. The copy program preserves subdirectory structure. The same filenames are used for source and destination. Implement the parallel file copy as follows .

1. Write a function called copydirectory that has the following prototype.

    void *copydirectory(void *arg) 

   The copydirectory function copies all the files from one directory to another directory. The directory names are passed in arg as two consecutive strings (separated by a null character). Assume that both source and destination directories exist when copydirectory is called. In this version, only ordinary files are copied and subdirectories are ignored. For each file to be copied , create a thread to run the copyfilepass function of Program 12.7. For this version, wait for each thread to complete before creating the next one.

2. Write a main program that takes two command-line arguments for the source and destination directories. The main program creates a thread to run copydirectory and then does a pthread_join to wait for the copydirectory thread to complete. Use this program to test the first version of copydirectory .

3. Modify the copydirectory function so that if the destination directory does not exist, copydirectory creates the directory. Test the new version.

4. Modify copydirectory so that after it creates a thread to copy a file, it continues to create threads to copy the other files. Keep the thread ID and open file descriptors for each copyfilepass thread in a linked list with a node structure similar to the following.

    typedef struct copy_struct {    char *namestring;    int sourcefd;    int destinationfd;    int bytescopied;    pthread_t tid;    struct copy_struct *next; } copyinfo_t; copyinfo_t *head = NULL; copyinfo_t *tail = NULL; 

   After the copydirectory function creates threads to copy all the files in the directory, it does a pthread_join on each thread in its list and frees the copyinfo_t structure.

5. Modify the copyfilepass function of Program 12.7 so that its parameter is a pointer to a copyinfo_t structure. Test the new version of copyfilepass and copydirectory .

6. Modify copydirectory so that if a file is a directory instead of an ordinary file, copydirectory creates a thread to run copydirectory instead of copyfilepass . Test the new function.

7. Devise a method for performing timings to compare an ordinary copy with the threaded copy.

8. If run on a large directory, the program may attempt to open more file descriptors or more threads than are allowed for a process. Devise a method for handling this situation.

9. See whether there is a difference in running time if the threads have scope PTHREAD_SCOPE_SYSTEM instead of PTHREAD_SCOPE_PROCESS .