POSIX

Table of Contents

http://pubs.opengroup.org/onlinepubs/9699919799/

This page is based on POSIX.1-2008 2016 Edition

POSIX defines the operating system interface. The starndard contains volumes:

I found most of them are not that interesting, except Base Definition section 9 regular expression. This definition is used by many shell utilities such as awk.

1 Tmp

sleep 

#include <unistd.h>
unsigned int sleep(unsigned int seconds); // seconds
int usleep(useconds_t useconds); // microseconds
int nanosleep(const struct timespec *rqtp, struct timespec *rmtp);

2 Regular Expression

2.1 Definition

The search for a matching starts at the beginning of string, and stops when the first sequence matching is found. If the pattern can match several string at a start point, the longest such sequence is matched. In other word, the longest of the leftmost matches.

Similarly Each subpattern (capturing group?), from left to right, shall also match the longest possible string. E.g. when matching \(.*\).*, the (\1) is the whole string.

The end of the string should be a NUL. Some utilities use <newline>.

2.2 Basic Regular Expressions (BRE)

Special characters

  • <period>, <left-square-bracket>, <baclslash>
    • when NOT in Bracket Expression
    • Match any character other than NUL
  • <asterisk>
    • when NOT in Bracket Expression
    • when NOT the first of entire BRE (after initial ^ if any)
    • when NOT the first of subexpression (after initial ^ if any)
  • circumflex>
    • when used as the first of the entire BRE
    • when used as the first in Bracket Expression
  • <dollar-sign>
    • when used as the last of entire BRE

2.2.1 Bracket Expression

[^]…[:alnum:]..1-8.-]

  • the close bracket can be ordinary if it is the first (after intial ^ is any)
  • hyphen(-) can be ordinary if it is first of last. Put it last if you want to use it with close bracket above
  • hyphen is inclusive
  • ^ immediately after left bracket turns it into a non-matching list, a.k.a. matches any character except these.
  • [:slnum:] is only valid inside bracket expression. It is called character class expression. All such expressions:
    • alnum, cntrl, lower, upper, space, alpha, digit
    • print, blank, graph, punct, xdigit

2.2.2 Matching Multiple Characters

  • *
  • \(\) is used. It can be arbitrarily nested.
  • \N is back reference. It shall match the same string as was matched by N-th sub-expression, it can be empty.
  • \{m\}, \{m,\}, \{m,n\}: inclusive

2.2.3 Precedence

From high to low:

  • [::]
  • escape \
  • bracket expression
  • subexpression/back reference
  • multiple character (* and \{m,n\}) (+? for ERE)
  • concatenation
  • anchor
  • (| for ERE)

2.3 Extended Regular Expressions (ERE)

  • () are special
  • +?{ are special
  • | is special

Note that no word begin in the standard.

3 pThread

#include <pthread.h>
pthread_create (thread, attr, start_routine, arg)
pthread_exit (status)
pthread_join (threadid, status)
pthread_detach (threadid)

3.1 Create threads

If main() finishes before the threads it has created, and exits with pthreadexit(), the other threads will continue to execute. Otherwise, they will be automatically terminated when main() finishes. 

  #define NUM_THREADS     5

  struct thread_data{
    int  thread_id;
    char *message;
  };

  int main() {
    pthread_t threads[NUM_THREADS];
    struct thread_data td[NUM_THREADS];

    int rc;
    int i;

    for( i=0; i < NUM_THREADS; i++ ){
      td[i].thread_id = i;
      td[i].message = "This is message";
      rc = pthread_create(&threads[i], NULL, PrintHello, (void *)&td[i]);
      if (rc){
        cout << "Error:unable to create thread," << rc << endl;
        exit(-1);
      }
    }
    pthread_exit(NULL);
  }

3.2 Join and Detach

  int main () {
    int rc;
    int i;
        
    pthread_t threads[NUM_THREADS];
    pthread_attr_t attr;
    void *status;

    // Initialize and set thread joinable
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

    for( i=0; i < NUM_THREADS; i++ ){
      cout << "main() : creating thread, " << i << endl;
      rc = pthread_create(&threads[i], &attr, wait, (void *)i );
                
      if (rc){
        cout << "Error:unable to create thread," << rc << endl;
        exit(-1);
      }
    }

    // free attribute and wait for the other threads
    pthread_attr_destroy(&attr);
        
    for( i=0; i < NUM_THREADS; i++ ){
      rc = pthread_join(threads[i], &status);
                
      if (rc){
        cout << "Error:unable to join," << rc << endl;
        exit(-1);
      }
                
      cout << "Main: completed thread id :" << i ;
      cout << "  exiting with status :" << status << endl;
    }

    cout << "Main: program exiting." << endl;
    pthread_exit(NULL);
  }

4 std::thread