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Tuesday, September 30, 2014
 
Programming in C: Few Tidbits #3

1) Not able to redirect the stdout output from a C program/application to a file

Possible cause:

Buffered nature of standard output (stdout) stream. Might be waiting for a newline character, for the buffer to be full, or for some other condition to be met based on implementation.

Few potential workarounds:


2) Printing ("escaping" maybe?) a percent sign (%) in a printf formatted string

Conversion/format specifiers start with a % sign, and using the slash sequence to escape the % sign in strings that are not format specifiers usually does not work. Check the following example out.

eg.,

Executing the following code:

        int pct = 35;
        printf("\n%d%", pct);

.. results in:

35, but not 35% as one would expect.

Format specifier "%%" simply prints the percent sign - so, the desired result can be achieved by replacing "%d%" with "%d%%" in printf statement.

        int pct = 35;
        printf("\n%d%%", pct);

.. shows:

35% as expected

(web search keywords: C printf conversion specification)


3) Duplicating a structure

If the structure has no pointers, assigning one struct to another struct duplicates the structure. The same effect can be achieved by using memcpy() too, but it is not really necessary. After the execution of struct assignment, there will be two copies of struct with no dependency - so, they can be operated independently without impacting the other. The following sample code illustrates this point.

eg., #1
 ...
 ...

 typedef struct human {
  int accno;
         int age;
 } person;

 ...
 ...

 person guy1, guy2;

 guy1.accno = 20202;
 guy1.age = 10;

 guy2 = guy1;

 printf("\nAddress of:\n\t-> guy1: %p. guy2: %p", guy1, guy2);

 printf("\n\nBefore update:\n");
 printf("\naccno of:\n\t-> guy1: %d. guy2: %d", guy1.accno, guy2.accno);
 printf("\nage of:\n\t-> guy1: %d. guy2: %d", guy1.age, guy2.age);

 guy1.age = 15;
 guy2.accno = 30303;

 printf("\n\nAfter update:\n");
 printf("\naccno of:\n\t-> guy1: %d. guy2: %d", guy1.accno, guy2.accno);
 printf("\nage of:\n\t-> guy1: %d. guy2: %d", guy1.age, guy2.age);

 ...
 ...
 

Execution outcome:

Address of:
        -> guy1: ffbffc38. guy2: ffbffc30

Before update:

accno of:
        -> guy1: 20202. guy2: 20202
age of:
        -> guy1: 10. guy2: 10

After update:

accno of:
        -> guy1: 20202. guy2: 30303
age of:
        -> guy1: 15. guy2: 10

On the other hand, if the structure has pointer variable(s), duplication of a structure using assignment operator leads to pointer variables in both original and copied structures pointing to the same block of memory - thus creating a dependency that could potentially impact both pointer variables with unintended consequences. The following sample code illustrates this.

eg., #2
 ...
 ...

 typedef struct human {
         int *accno;
         int age;
 } person;

 ...
 ...

 person guy1, guy2;

 guy1.accno = malloc(sizeof(int));
 *(guy1.accno) = 20202;

 guy1.age = 10;
 guy2 = guy1;
 
 ...
 ...

 guy1.age = 15;
 *(guy2.accno) = 30303;

 ...
 ...
Execution outcome:
Address of:
        -> guy1: ffbffb48. guy2: ffbffb40

Before update:

accno of:
        -> guy1: 20202. guy2: 20202
age of:
        -> guy1: 10. guy2: 10

After update:

accno of:
        -> guy1: 30303. guy2: 30303
age of:
        -> guy1: 15. guy2: 10

Few people seem to refer this kind of duplication as shallow copy though not everyone agrees with the terminology.

If the idea is to clone an existing struct variable that has one or more pointer variables, then to work independently on the clone without impacting the struct variable it was cloned from, one has to allocate memory manually for pointer variables and copy data from source structure to the destination. The following sample code illustrates this.

eg., #3
 ...
 ...

 typedef struct human {
         int *accno;
         int age;
 } person;

 ...
 ...

 person guy1, guy2;

 guy1.accno = malloc(sizeof(int));
 *(guy1.accno) = 20202;

 guy1.age = 10;

 guy2.age = guy1.age;
 guy2.accno = malloc(sizeof(int));
 *(guy2.accno) = *(guy1.accno);

 ...
 ...

 guy1.age = 15;
 *(guy2.accno) = 30303;

 ...
 ...

Execution outcome:

Address of:
        -> guy1: ffbffaa8. guy2: ffbffaa0

Before update:

accno of:
        -> guy1: 20202. guy2: 20202
age of:
        -> guy1: 10. guy2: 10

After update:

accno of:
        -> guy1: 20202. guy2: 30303
age of:
        -> guy1: 15. guy2: 10

This style of explicit duplication is referred as deep copy by few people though not everyone agrees with the terminology.




Thursday, July 31, 2014
 
Programming in C: Few Tidbits #2

(1) ceil() returns an incorrect value?

ceil() rounds the argument upward to the nearest integer value in floating-point format. For example, calling ceil() with an argument (2/3) should return 1.

printf("\nceil(2/3) = %f", ceil(2/3));

results in:

ceil(2/3) = 0.000000

.. which is not the expected result.

However:

printf("\nceil((float)2/3) = %f", ceil((float)2/3));

shows the expected result.

ceil((float)2/3) = 1.000000

The reason for the incorrect result in the first attempt can be attributed to the integer division. Since both operands in the division operation are integers, it resulted in an integer division which discarded the fractional part.

Desired result can be achieved by casting one of the operands to float or double as shown in the subsequent attempt.

One final example for the sake of completeness.

printf("\nceil(2/(float)3) = %f", ceil(2/(float)2));
..
ceil(2/(float)3) = 1.000000

(2) Main difference between abort() and exit() calls

On a very high level: abort() sends SIGABRT signal causing abnormal termination of the target process without calling functions registered with atexit() handler, and results in a core dump. Some cleanup activity may happen.

exit() causes normal process termination after executing functions registered with the atexit() handler, and after performing cleanup activity such as flushing and closing all open streams.

If it is desirable to bypass atexit() registered routine(s) during a process termination, one way is to call _exit() rather than exit().

Of course, this is all high level and the information provided here is incomplete. Please check relevant man pages for detailed information.


(3) Current timestamp

The following sample code shows the current timestamp in two different formats. Check relevant man pages for more information.

#include <time.h>
..
char timestamp[80];
time_t now;
struct tm *curtime;

now = time(NULL);
curtime = localtime(&now);

strftime(timestamp, sizeof(timestamp), "%m-%d-%Y %X", curtime);

printf("\ncurrent time: %s", timestamp);
printf("\ncurrent time in a different format: %s", asctime(curtime));
..

Executing this code shows output

current time: 07-31-2014 22:05:42
current time in a different format: Thu Jul 31 22:05:42 2014

Labels:




Monday, June 30, 2014
 
Programming in C: Few Tidbits

.. with little commentary aside. Target audience: new programmers. These tips are equally applicable in C and C++ programming environments.

1. Duplicating a file pointer

Steps: find the integer file descriptor associated with the file stream using fileno() call, make a copy of the file descriptor using dup() call, and finally associate the file stream with the duplicated file descriptor by calling fdopen().

eg.,
FILE *fptr = fopen("file", "mode");

FILE *fptrcopy = fdopen( dup( fileno(fptr) ), "mode");

2. Capturing the exit code of a command that was invoked using popen()

Using pipes is one way of executing commands programmatically that are otherwise invoked from a shell. While pipes are useful in performing tasks other than executing shell commands, this tip is mainly about the exit code of a command (to figure out whether it succeeded or failed) that was executed using popen() API.

To capture the exit code, simply use the value returned by pclose(). This function call returns the termination status of the command that was executed as a child process. However the termination status of the child process is in the top 16 bits of the return value, so dividing the pclose() return value by 256 gives the actual exit code of the command that was executed.

eg.,
...
FILE *ptr;
int rc;

if ((ptr = popen("ls", "r")) != NULL) {
 rc = pclose(ptr)/256;
 printf("\nls: exit code = %d", rc);
}

if ((ptr = popen("ls -W", "r")) != NULL) {
 rc = pclose(ptr)/256;
 printf("\nls -W: exit code = %d", rc);
}
...

% ./<executable>

ls: exit code = 0
ls: illegal option -- W
ls -W: exit code = 2

3. Converting an integer to a string

Standard C library has implementation for converting a string to an integer (atoi()), but not for converting an integer to a string. One way to achieve the desired result is by using sprintf() function call, which writes formatted data to a string.

eg.,
int weight = 30;
char *wtstr = malloc(sizeof(char) * 3);

sprintf(wtstr, "%d", weight);
...

sprintf() can also be used to convert data in other data types such as float, double to string. Also see: man page for snprintf().


4. Finding the length of a statically allocated array

When size was not specified explicitly, simply divide the total size of the array by the size of the first array element.

eg.,
static const char *greeting[] = { "Hi", "Hello", "Hola", "Bonjour", "Namaste", "Ciao", "Ni Hao" };
int numgreetings = sizeof(greeting)/sizeof(greeting[0]);

After execution, numgreetings variable holds a value of 7. Note that sizeof(greeting[0]) is actually the size of a pointer to a character array.

Labels:




Saturday, May 17, 2014
 
Blast from the Past : The Weekend Playlist #6

Compared to the 80s, music in the 90s was equally good if not better. Artists let their imagination run wild -- that resulted in many memorable, bold and dark themed renditions. While the 80s were dominated by the cassette tapes, the rise of compact discs with better quality sound might have added fuel to music industry's growth engine in the 90s.

Enjoy the recollection.

Access previous playlists from the following locations:

    #1 (50s, 60s and 70s) | #2 (80s) | #3 (80s) | #4 (80s) | #5 (80s)

Audio-Visual material courtesy: YouTube. Other information: Wikipedia.

1. Bon Jovi - Blaze of Glory (1990)

Love the guitar bits. Featured in western, Young Guns II.

2. Radiohead - Creep (1992)

Some cool guitar trick in the middle earns it extra credit

3. Depeche Mode - Enjoy The Silence (1990)

Masters of Electronic music. Enjoy.

4. Jimmy Cliff - I Can See Clearly Now (1993)

Cover for Johnny Nash's 1972 original. Great song nevertheless.

5. Godsmack - Voodoo (1999)

Beware: dark video. My brother's old buddy Sudhir gets the credit for digging this one out.

6. Sting - Fields Of Gold (1993)

Enjoy. Tidbit: Sting (Gordon Summer) was associated with "The Police" too.

7. Coolio - Gangsta's Paradise (1995)

Cool song. Won a Grammy.

8. Blue Man Group - Synaesthetic (1999)

Pump up the volume, sit back and Enjoy

9. The Prodigy - Mindfields (1997)

Love the guitar riff though sampled from John Barry's "Hip's Trip". Featured in The Matrix.

10. The Smashing Pumpkins - 1979 (1996)

Music video won the "MTV Video Music Award for Best Alternative Video" in 1996

Labels:




Saturday, May 10, 2014
 
Solaris 11.2 Highlights [Part 2] in 4 Minutes or Less

Part 1: Solaris 11.2 Highlights in 6 Minutes or Less

Highlights contd.,

Package related ..

Minimal Set of System Packages

For the past few years, it is one of the hot topics -- what is the bare minimum [set of packages] needed to run applications. There were a number of blog posts and few technical articles around creating minimal Solaris configurations. Finally users/customers who wish to have their OS installed with minimal set of required system packages for running most of the applications in general, can just install solaris-minimal-server package and not worry about anything else such as removing unwanted packages.

# pkg install pkg:/group/system/solaris-minimal-server

Oracle Database Pre-requisite Package

Until Solaris 11.1, it is up to the users to check the package dependencies and make sure to have those installed before attempting to install Oracle database software especially using graphic installer. Solaris 11.2 frees up the users from the burden of checking and installing individual [required] packages by providing a brand new package called oracle-rdbms-server-12cR1-preinstall. Users just need to install this package for a smoother database software installation later.

# pkg install pkg:/group/prerequisite/oracle/oracle-rdbms-server-12cR1-preinstall

Mirroring a Package Repository

11.2 provides the ability to create local IPS package repositories and keeps them in synch with the IPS package repositories hosted publicly by Oracle Corporation. The key in achieving this is the SMF service svc:/application/pkg/mirror. The following webpage has the essential steps listed on a high-level.

How to Automatically Copy a Repository From the Internet

Another enhancement is the cloning of a package repository using --clone option of pkgrecv command.

Observability related ..

Network traffic diagnostics:

A brand new command, ipstat(1M), reports IP traffic statistics.

# ipstat -?
Usage:	ipstat [-cmnrt] [-a address[,address...]] [-A address[,address...]]
[-d d|u] [-i interface[,interface...]] [-l nlines] [-p protocol[,protocol...]]
[-s key | -S key] [-u R|K|M|G|T|P] [-x opt[=val][,opt[=val]...]]

# ipstat -uM 5

SOURCE                     DEST                       PROTO    INT        BYTES
etc5mdbadm01.us.oracle.com etc2m-appadm01.us.oracle.c TCP      net8       76.3M
etc2m-appadm01.us.oracle.c etc5mdbadm01.us.oracle.com TCP      net8        0.6M
dns1.us.oracle.com         etc2m-appadm01.us.oracle.c UDP      net8        0.0M
169.254.182.76             169.254.182.77             UDP      net20       0.0M
...

Total: bytes in: 76.3M bytes out:  0.6M

Another new command, tcpstat(1M), reports TCP and UDP traffic statistics.

# tcpstat -?
Usage:	tcpstat [-cmnrt] [-a address[,...]] [-A address[,...]] [-d d|u] [-i pid[,...]] 
[-l nlines] [-p port[,...]] [-P port[,...]] [-s key | -S key] [-x opt[=val][,...]] 
[-z zonename[,...]] [interval [count]]

# tcpstat 5

ZONE         PID PROTO  SADDR             SPORT DADDR             DPORT   BYTES
global      1267 TCP    etc5mdbadm01.us.  42972 etc2m-appadm01.u     22   84.3M
global      1267 TCP    etc2m-appadm01.u     22 etc5mdbadm01.us.  42972   48.0K
global      1089 UDP    169.254.182.76      161 169.254.182.77    33436  137.0 
global      1089 UDP    169.254.182.77    33436 169.254.182.76      161   44.0 
...
...

Total: bytes in: 84.3M bytes out: 48.4K

# tcpstat -i 43982 5		<-- TCP stats for a given pid

ZONE         PID PROTO  SADDR             SPORT DADDR             DPORT   BYTES
global     43982 TCP    etc2m-appadm01.u  43524 etc5mdbadm02.us.     22   73.7M
global     43982 TCP    etc5mdbadm02.us.     22 etc2m-appadm01.u  43524   41.9K

Total: bytes in: 42.1K bytes out: 73.7M

Up until 11.1, it is not so straight-forward to figure out what process created a network endpoint -- one has to rely on a combination of commands such as netstat, pfiles or lsof and proc filesystem (/proc) to extract that information. Solaris 11.2 attempts to make it easy by enhancing the existing tool netstat(1M). Enhanced netstat(1M) shows what user, pid created and control a network endpoint. -u is the magic flag.

#  netstat -aun			<-- notice the -u flag in netstat command; and User, Pid, Command columns in the output

UDP: IPv4
   Local Address        Remote Address      User    Pid      Command       State
-------------------- -------------------- -------- ------ -------------- ----------
      *.*                                 root        162 in.mpathd      Unbound
      *.*                                 netadm      765 nwamd          Unbound
      *.55388                             root        805 picld          Idle
	...
	...

TCP: IPv4
   Local Address        Remote Address      User     Pid     Command     Swind  Send-Q  Rwind  Recv-Q    State
-------------------- -------------------- -------- ------ ------------- ------- ------ ------- ------ -----------
10.129.101.1.22      10.129.158.100.38096 root       1267 sshd           128872      0  128872      0 ESTABLISHED
192.168.28.2.49540   192.168.28.1.3260    root          0       2094176      0 1177974      0 ESTABLISHED
127.0.0.1.49118            *.*            root       2943 nmz                 0      0 1048576      0 LISTEN
127.0.0.1.1008             *.*            pkg5srv   16012 httpd.worker        0      0 1048576      0 LISTEN
	...

[x86 only] Memory Access Locality Characterization and Analysis

Solaris 11.2 introduced another brand new tool, numatop(1M), that helps in characterizing the NUMA behavior of processes and threads on systems with Intel Westmere, Sandy Bridge and Ivy Bridge processors. If not installed by default, install the numatop package as shown below.

# pkg install pkg:/diagnostic/numatop

Performance related ..

This is a grey area - so, just be informed that there are some ZFS and Oracle database related performance enhancements.

Starting with 11.2, ZFS synchronous write transactions are committed in parallel, which should help improve the I/O throughput.

Database startup time has been greatly improved in Solaris 11 releases -- it's been further improved in 11.2. Customers with databases that use hundreds of Gigabytes or Terabyte(s) of memory will notice the improvement to the database startup times. Other changes to asynchronous I/O, inter-process communication using event ports etc., help improve the performance of the recent releases of Oracle database such as 12c.

Miscellaneous ..

Java 8

Java 7 is still the default in Solaris 11.2 release, but Java 8 can be installed from the IPS package repository.

eg.,

# pkg install pkg:/developer/java/jdk-8		<-- Java Development Kit
# pkg install pkg:/runtime/java/jre-8		<-- Java Runtime

Bootable USB Media

Solaris 11.2 introduces the support for booting SPARC systems from USB media. Use Solaris Distribution Constructor (requires distribution-constructor package) to create the USB bootable media, or copy a bootable/installation image to the USB media using usbcopy(1M) and dd(1M) commands.

Oracle Hardware Management Pack

Oracle Hardware Management Pack is a set of tools that are integrated into the Solaris OS distribution, that show the existing hardware configuration, help configure hardware RAID volumes, update server firmware, configure ILOM service processor, enable monitoring the hardware using existing tools etc., Look for pkg:/system/management/hmp/hmp-* packages.

Few other interesting packages:

Parallel implementation of bzip2 : compress/pbzip2
NVM Express (nvme) utility : system/storage/nvme-utilities
Utility to administer cluster of servers : terminal/cssh

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