Exercise (due March 9)
●Exercise 7.15: Reaction-Time Tester.
Write a program that measures how quickly a user can respond. The program waits for a random interval of time then prints a single digit on the screen. The user has to type that digit as quickly as possible. The program records how long it takes the user to respond. Your program should perform 10 such tests and report the minimum, maximum and average response time. (Hint, read the manual page for gettimeofday).
Processes
●Monitoring Process
● ps
●pstree
●parent process
●child process
●exec, execvp
●fork
exec
EXEC(3) Linux Programmer's Manual EXEC(3)
NAME
execl, execlp, execle, execv, execvp - execute a file
SYNOPSIS
#include <unistd.h>
extern char **environ;
int execl(const char *path, const char *arg, ...);
int execlp(const char *file, const char *arg, ...);
int execle(const char *path, const char *arg , ..., char * const envp[]);
int execv(const char *path, char *const argv[]);
int execvp(const char *file, char *const argv[]);
How does a program execute a program
●program reads command line
●program calls execvp
●main()
{char*arglist[4];
arglist[0] = "ls";
arglist[1] = "-l";
arglist[2] = "/bin";
arglist[3] = 0 ;
execvp( "ls" , arglist );
printf("ls is done. bye\n");}
Fork
NAME
fork - create a child process
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
pid_t fork(void);
DESCRIPTION
fork creates a child process that differs from the parent process only
in its PID and PPID, and in the fact that resource utilizations are set
to 0. File locks and pending signals are not inherited.
Under Linux, fork is implemented using copy-on-write pages, so the only
penalty incurred by fork is the time and memory required to duplicate
the parent's page tables, and to create a unique task structure for the
child.
RETURN VALUE
On success, the PID of the child process is returned in the parent's
thread of execution, and a 0 is returned in the child's thread of exe-
cution. On failure, a -1 will be returned in the parent's context, no
child process will be created, and errno will be set appropriately.
getpid
NAME
getpid, getppid - get process identification
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
pid_t getpid(void);
pid_t getppid(void);
DESCRIPTION
getpid returns the process ID of the current process. (This is often
used by routines that generate unique temporary file names.)
getppid returns the process ID of the parent of the current process.
fork
●What does this fragment do?
printf(“mypid=%d\n”,getpid());
n=fork();
printf(“mypid=%d,n=%d\n”,getpid(),n);
●What does this fragment do?
printf(“mypid=%d\n”,getpid());
fork();
fork();
fork();
printf(“mypid=%d\n”,getpid());
sleeping while child works:wait
NAME
wait - wait for process termination
SYNOPSIS
#include <sys/types.h>
#include <sys/wait.h>
pid_t wait(int *status);
DESCRIPTION
The wait function suspends execution of the current process until a
child has exited, or until a signal is delivered whose action is to
terminate the current process or to call a signal handling function.
If a child has already exited by the time of the call (a so-called
"zombie" process), the function returns immediately. Any system
resources used by the child are freed.
sleeping while child works:wait
NAME
waitpid - wait for process termination
SYNOPSIS
#include <sys/types.h>
#include <sys/wait.h>
pid_t waitpid(pid_t pid, int *status, int options);
DESCRIPTION
The waitpid function suspends execution of the current process until a
child as specified by the pid argument has exited, or until a signal is
delivered whose action is to terminate the current process or to call a
signal handling function. If a child as requested by pid has already
exited by the time of the call (a so-called "zombie" process), the
function returns immediately. Any system resources used by the child
are freed.
:
sleeping while child works:wait
The value of options is an OR of zero or more of the following con-
stants:
WNOHANG
which means to return immediately if no child has exited.
WUNTRACED
which means to also return for children which are stopped (but
not traced), and whose status has not been reported. Status for
traced children which are stopped is provided also without this
option.
:
sleeping while child works:wait
The value of pid can be one of
< -1 which means to wait for any child process whose process group ID
is equal to the absolute value of pid.
-1 which means to wait for any child process; this is the same
behaviour which wait exhibits.
0 which means to wait for any child process whose process group ID
is equal to that of the calling process.
>0 which means to wait for the child whose process ID is equal to the
value of pid
Components of a Process, /proc
●
●
PROC(5) Linux Programmer's Manual PROC(5)
NAME
proc - process information pseudo-filesystem
DESCRIPTION
The proc filesystem is a pseudo-filesystem which is used as an inter-
face to kernel data structures. It is commonly mounted at /proc. Most
of it is read-only, but some files allow kernel variables to be
changed.
Components of a Process, /proc
●
●
/proc/[number]/stat
Status information about the process. This is used by ps(1). It is defined in /usr/src/linux/fs/proc/array.c.
The fields, in order, with their proper scanf(3) format specifiers, are:
pid %d The process id.
comm %s
The filename of the executable, in parentheses. This is
visible whether or not the executable is swapped out.
state %c
One character from the string "RSDZTW" where R is run-
ning, S is sleeping in an interruptible wait, D is wait-
ing in uninterruptible disk sleep, Z is zombie, T is
traced or stopped (on a signal), and W is paging.
ppid %d
The PID of the parent.
pgrp %d
The process group ID of the process.
session %d
The session ID of the process.
tty_nr %d
The tty the process uses.
tpgid %d
process info system calls
chdir(path)
fchdir(fd)
getcwd()
ctermid()
Return the filename corresponding to the controlling terminal of the process.
getegid()
Return the effective group id of the current process. This corresponds to the `set id' bit on the file being executed in the current process.
geteuid()
Return the current process' effective user id.
process info system calls
getgid()
Return the real group id of the current process.
getgroups()
Return list of supplemental group ids associated with the current process.
getlogin()
Return the name of the user logged in on the controlling terminal of the process.
getpgid(pid)
Return the process group id of the process with process id pid.
getpgrp()
Return the id of the current process group.
process info system calls
getpid()
Return the current process id.
getppid()
Return the parent's process id..
getuid()
Return the current process' user id..
getenv(varname)
Return the value of the environment variable varname.
putenv(string)
Set the environment variable as defined by string.
process info system calls
setegid(egid)
Set the current process' effective group id.
seteuid(euid)
Set the current process's effective user id. Availability: Unix.
setgid(gid)
Set the current process' group id. Availability: Unix.
setgroups(size, list)
Set the list of supplemental group ids associated with the current process to whose store in list
setpgrp(pid, pgid)
Sets the process group ID of the process specified by pid to pgid.
process info system calls
setreuid(ruid, euid)
Set the current process's real and effective user ids.
setregid(gid, egid)
Set the current process's real and effective group ids.
getsid(pid)
Returns the session ID of the calling process for process pif.
setsid()
Run a program in a new session
setuid(uid)
Set the current process' user id.
Environ
#include <unistd.h>
extern char **environ;
int main(int agrc, char **argv){
char **a;
a=environ;
printf("Starting myenviron, my environment variables are:\n");
while (*a){
printf("\t%s\n",*a);
a++;
}
}
sysinfo
NAME
sysinfo - returns information on overall system statistics
SYNOPSIS
#include <sys/sysinfo.h>
int sysinfo(struct sysinfo *info);
DESCRIPTION
Until Linux 2.3.16, sysinfo used to return information in the following
structure:
sysconf
NAME
sysconf - Get configuration information at runtime
SYNOPSIS
#include <unistd.h>
long sysconf(int name);
DESCRIPTION
POSIX allows an application to test at compile- or run-time whether
certain options are supported, or what the value is of certain config-
urable constants or limits.
Exercise 8.12
●Determine how a shell responses to SIGINT and SIGQUIT generated from the keyboard. Modify psh2.c so that it responds in the same way. Hint: it might be helpful to investigate what the SA_RESTART flag does in sigaction.
Studying Windows Internals
Look at www.sysinternals.com
●Process Explorer
●Handle
●ListDLLs
●Pstools
●Regmon
OVERVIEW
●A Windows process contains its own independent virtual address space with both code and data
●Each process contains one or more independently executed threads
●The Windows thread is the basic executable unit
●A process can
●Create new threads within the processes
●Create new, independent processes
●Manage communication and synchronization between these objects
●For now we consider only a single thread within a process
Windows PROCESSES HAVE
●One or more threads
●Virtual address space which is distinct from other processes’ address spaces
●Except for shared memory-mapped files
●One or more code segments
●One or more data segments containing global variables
●Environment strings with environment variable information
●The process heap
●Resources such as open handles and other heaps
THREADS
●Share the code, global variables, environment strings and resources in a process
●Are independently scheduled
●Have a stack for procedure calls, interrupts, etc.
●Have Thread Local Storage (TLS)—pointers giving each thread the ability to allocate storage to create its own unique data environment
●Have an argument (on the stack) from the creating thread
●Can also be unique for each thread
●Have a context structure, maintained by the kernel, with machine register values
A PROCESS AND ITS THREADS
Code
Global Variables
Process Heap
Process Resources
Open Files, Heaps,
· · ·
Environment Block
· · ·
Thread 1
TLS
Stack
Thread N
TLS
Stack
PROCESS CREATION
BOOL CreateProcess (LPCTSTR lpImageName,
LPTSTR lpCommandLine,
LPSECURITY_ATTRIBUTES lpsaProcess,
LPSECURITY_ATTRIBUTES lpsaThread,
BOOL bInheritHandles, DWORD dwCreate,
LPVOID lpvEnvironment, LPCTSTR lpCurDir,
LPSTARTUPINFO lpsiStartInfo,
LPPROCESS_INFORMATION lppiProcInfo)
Return: TRUE only if the process and thread are successfully created
PROCESS CREATION
Parameters
lpImageName — Specifies the executable program
lpCommandLine — Specifies the command line arguments
lpsaProcess — Points to the process security attribute structure
lpsaThread — Points to the thread security attribute structure
●(NULL implies default security)
PROCESS CREATION
bInheritHandles — This is a “master switch” to indicate that the new process can inherit handles from the parent
●Individual handles must still be specified as inheritable
●A typical use is to redirect standard I/O — there are numerous examples in the lab exercises
PROCESS CREATION
dwCreate — Combines flags, including:
●CREATE_SUSPENDED — The primary thread is in
a suspended state and will only run when
ResumeThread is called
●DETACHED_PROCESS — Creates a process
without a console
●CREATE_NEW_CONSOLE — Gives the new
process a console
●(These two are mutually exclusive. If neither is set, the
process inherits the parent’s console.)
●CREATE_NEW_PROCESS_GROUP — Specifies
that the new process is the root of a new process group
PROCESS CREATION
lpvEnvironment — Points to an environment block for the new process. If NULL, the parent’s environment is used. Contains name/value strings, such as search path.
lpCurDir — Drive and directory for the new process
●If NULL, parent’s is used)
lpsiStartInfo — Main window appearance for the new process
lppiProcInfo — Structure to contain the returned process and thread handles and identification
PROCESS CREATION
typedef struct _PROCESS_INFORMATION {
HANDLE hProcess;
HANDLE hThread;
DWORD dwProcessId;
DWORD dwThreadId;
} PROCESS_INFORMATION;
Processes and threads need both handles and IDs
●ID is unique to the object for its lifetime in all processes
●There may be several handles for a given process
●Handles are used with many general-purpose functions
PROCESS CREATION
typedef struct _STARTUPINFO {
/* Lots of information controlling the window */
DWORD dwFlags;
HANDLE hStdInput;
HANDLE hStdOutput;
HANDLE hStdError;
} STARTUPINFO;
PROCESS CREATION
●Setting these handles before creating the process is a common way to redirect the new process’ standard I/O
●Set dwFlags to STARTF_USESTDHANDLES to enable redirection
●Use GetStartupInfo (&StartupInfo) to fill in the structure from the parent’s values