Add pthread Support to SageX

Make it possible to use C-level POSIX threads from SageX programs.

1. Create a pxi file with the pthread.h functions declared.

• Here's a start:

cdef extern from "pthread.h":
    ctypedef int pthread_t       # actual type will be used by Pyrex below...
    ctypedef int pthread_attr_t     
    int pthread_create(pthread_t *thread, 
                       pthread_attr_t *attr,
                       void *(*start_routine)(void *), 
                       void *arg)
    int pthread_join(pthread_t thread, void **value_ptr)
    void pthread_exit(void *value_ptr)

The file should be nicely documented, etc.

2. Create spyx files that illustrate how to use various threading constructs

Here's an example (you can paste this into foo.spyx, load it, and call go(10)):

cdef extern from "pthread.h":
    ctypedef int pthread_t       # actual type will be used by Pyrex below...
    ctypedef int pthread_attr_t     
    int pthread_create(pthread_t *thread, 
                       pthread_attr_t *attr,
                       void *(*start_routine)(void *), 
                       void *arg)
    int pthread_join(pthread_t thread, void **value_ptr)
    void pthread_exit(void *value_ptr)

cdef extern from "unistd.h":
    unsigned int sleep(unsigned int seconds)


cdef void *PrintHello(void *thread_id):
   printf("\n%d: Hello World...", thread_id)
   sleep(1)
   printf("Thread %d ending\n", thread_id)
   pthread_exit(NULL)

def go(int n):
    cdef pthread_t* threads
    threads = <pthread_t*> malloc(sizeof(pthread_t) * n)
    cdef int rc, t
    for t from 0 <= t < n:
        printf("Creating thread %d...", t)
        rc = pthread_create(&threads[t], NULL, PrintHello, <void*> t)
        if rc:
            printf("ERROR; return code from pthread_create() is %d\n", rc)
            return
    print('done creating all threads; now waiting')
    for t from 0 <= t < n:
        pthread_join(threads[t], <void**> NULL)
    free(threads)
    print('done freeing all memory used to store thread data.')


cdef int n
cdef void *PrintDot(void* thread_id):
    global n
    while 1:
        printf(".. %d ..\n", n)
        sleep(3)
        n += 1

def print_dot():
    cdef pthread_t t
    pthread_create(&t, NULL, PrintDot, <void*> NULL)

def nval():
    print n