Modify the main function in server.c to handle 's' and 'g' commands as well as creating new threads (blank line - no command)
Define a global struct in server.c with members of type:
and initialize. What initial values?
Create three functions to control the database client threads
Use the global struct in these functions.
What should each one do and how should each one be implemented?
Add an member of type pthread_rwlock_t to the node type Node_t
Modify Node_constructor function to initialize this extra member.
Use a enum for the two lock types (in db.c is ok):
enum lock_type = {dblock_read, dblock_write};Add a parameter to the search function in db.c for lock_type.
Modify query, add, and xremove functions to call search with the appropriate lock_type value. E.g., query should call with dblock_read.
For fine grain locking, only nodes that are involved in being changed need be locked. As search moves down the tree, how many nodes need to be locked?
Before calling search, query, add, and xremove should lock the head node.
When search returns, query, add, and xremove should unlock node(s) that remain locked, but this depends on which function called search and/or whether the search was successful (found the name).
Problem: Want to block threads until all n have been blocked, then release all (possibly repeat).
Not a solution:
1 pthread_mutex_lock(&m);
2 if (++count == number) {
3
4 pthread_cond_broadcast(&cond_var);
5 } else {
6 while (!(count == number))
7 {
8 pthread_cond_wait(&cond_var, &m);
9 }
10 }
11 pthread_mutex_unlock(&m);
Also not a solution:
1 pthread_mutex_lock(&m);
2 if (++count == number) {
3
4 pthread_cond_broadcast(&cond_var);
5 count = 0;
6 } else {
7 while (!(count == number))
8 {
9 pthread_cond_wait(&cond_var, &m);
10 }
11 }
12 pthread_mutex_unlock(&m);
Should be, but isn't a POSIX solution
1 pthread_mutex_lock(&m);
2 if (++count == number) {
3
4 pthread_cond_broadcast(&cond_var);
5 count = 0;
6 } else {
7 pthread_cond_wait(&cond_var, &m);
8 }
9 pthread_mutex_unlock(&m);
1 pthread_mutex_lock(&m);
2 if (++count < number) {
3 int my_generation = generation;
4 while(my_generation == generation) {
5 pthread_cond_wait(&waitQ, &m);
6 }
7 } else {
8 count = 0;
9 generation++;
10 pthread_cond_broadcast(&waitQ);
11 }
12 pthread_mutex_unlock(&m);
What is the errno problem? the solution?
Problem? Solution?
Pending Signals
Blocked Signals
Signal Handlers
What are the possible choices? What choices were made for POSIX?
The sigwait function blocks until a signal in the specified set is received.
What if more than one of those signals received?
What if several threads are calling sigwait for the same signal(s)?
computation_state_t state;
sigset_t set;
main( ) {
pthread_t thread;
sigemptyset(&set);
sigaddset(&set, SIGINT);
sigprocmask(SIG_BLOCK,
&set, 0);
pthread_create(&thread, 0, monitor, 0);
long_running_procedure( );
}
void *monitor( ) {
int sig;
while (1) {
sigwait(&set, &sig);
display(&state);
}
return(0);
}
pthread_kill(thrd) sends a signal to thread with id thrd.
pthread_cancel(thrd) terminates the thread with id thrd, but ...
Default: enabled and deferred
pthread_cleaup_push(func, func_arg)
pthread_cleanup_pop(int flag)
What does deferred mean?
What are valid cancellation points?
read and write are cancellation points
pthread_cond_wait is a cancellation point, but ...
pthread_mutex_lock is NOT a cancellation point.
What does this code do if it is "cancelled while in the pthread_cond_wait call?
Does the thread leaving the mutex locked?
Does the cleanup try to unlock a mutex that is not locked?
1 pthread_mutex_lock(&m);
2 pthread_cleanup_push(pthread_mutex_unlock, &m);
3 while(should_wait)
4 pthread_cond_wait(&cv, &m);
5
6 // . . . (code containing other cancellation points)
7
8 pthread_cleanup_pop(1);
On Linux (cdmlinux or you if you have linux installed, you can use your installation)
Implement user level thread library: i.e., could be a substitute for POSIX pthreads.
80% of code provided!
19 functions to write.
Test suite provided. (9 tests, can be run individually or all at once)
A make target (nyi) displays the function, line number, file of code that is NOT_YET_IMPLEMENTED.