I am reading through the pthreads tutorial and had a question on the example they have given for condition variables. Here is the code snippet:
This is what the thread waiting on the condition variables doing:
Why is the check for count in the while loop and not an if ?
From what I see, the only advantage of it being in the while loop is if by any chance the signaling thread incorrectly signaled the waiting thread (i.e. it sent a signal even though the value of count was still < COUNT_LIMIT). But in that case, I would expect the code to be something like this:
Hello everybody,
I am having problem in converting byte array variables to Hexa String variables for Linux. I have done, converting byte array variables to Hexa String variables for Windows but same function doesn't work for linux. Is there any difference in OS ? The code for Windows is given... (2 Replies)
I am trying to understand the exact difference between condition variables and mutexes in thread synchronization ?. I know mutex will control the thread access to shared data and condition variables will be useful for waiting for certain event or condition to occur . But I couldn't understand
why... (2 Replies)
Executed the following if conditions .. and got different results .
only (( )) gave correct o/p with all scenarios .
Can anybody please let me know what is the difference between and ] and ((condition)) when used with if condition.
And why each condition gave different result.
1.... (2 Replies)
hi,
I have some problems in my simple script about the redirect echo stdout command inside a condition. Why is the echo command inside the elif still execute in the else command
Here are my simple script
After check on the two diff output the echo stdout redirect is present in two diff... (3 Replies)
I am trying the understand the conditional variable concept.
I went through the following site:
https://computing.llnl.gov/tutorials/pthreads/#ConditionVariables
I understand that condition variables allow threads to synchronize based upon the VALUE of data.
When the data acheives a particular... (2 Replies)
HI
My doubt may be basic one but I need to get it clarified..
When i use "if" condition that checks for many AND, OR logical conditions
like
if ]; then
return 0
fi
Even the if condition fails it returns as zero.. Any clue..
But if i add else condition like
if ]; ... (2 Replies)
Hi All,
i have a requirement where i have to run a script with at least 25 arguements and position of arguements can also change. the unapropriate way is like below. can we achieve this in more good and precise way??
#!/bin/ksh
##script is sample.ksh
age=$1
gender=$2
class=$3
.
.
.... (3 Replies)
Sometimes it is handy to protect long scripts in C++.
The following syntax works fine for simple commands:
#define SHELLSCRIPT1 "\
#/bin/bash \n\
echo \"hello\" \n\
"
int main ()
{
cout <<system(SHELLSCRIPT1);
return 0;
}
Unfortunately for there are problems for:
1d arrays:... (10 Replies)
Below are three variables, which I want to pass into variable RESULT1
username1=userid
poihostname1=dellsys.com
port1=8080
How can I pass these variables into below code...
RESULT1=$((ssh -n username1@poihostname1 time /usr/sfw/bin/wget --user=sam --password=123 -O /dev/null -q... (4 Replies)
Discussion started by: manohar2013
4 Replies
LEARN ABOUT PHP
condition
condition(5) Standards, Environments, and Macros condition(5)NAME
condition - concepts related to condition variables
DESCRIPTION
Occasionally, a thread running within a mutex needs to wait for an event, in which case it blocks or sleeps. When a thread is waiting for
another thread to communicate its disposition, it uses a condition variable in conjunction with a mutex. Although a mutex is exclusive and
the code it protects is sharable (at certain moments), condition variables enable the synchronization of differing events that share a
mutex, but not necessarily data. Several condition variables may be used by threads to signal each other when a task is complete, which
then allows the next waiting thread to take ownership of the mutex.
A condition variable enables threads to atomically block and test the condition under the protection of a mutual exclusion lock (mutex)
until the condition is satisfied. If the condition is false, a thread blocks on a condition variable and atomically releases the mutex that
is waiting for the condition to change. If another thread changes the condition, it may wake up waiting threads by signaling the associated
condition variable. The waiting threads, upon awakening, reacquire the mutex and re-evaluate the condition.
Initialize
Condition variables and mutexes should be global. Condition variables that are allocated in writable memory can synchronize threads among
processes if they are shared by the cooperating processes (see mmap(2)) and are initialized for this purpose.
The scope of a condition variable is either intra-process or inter-process. This is dependent upon whether the argument is passed implic-
itly or explicitly to the initialization of that condition variable. A condition variable does not need to be explicitly initialized. A
condition variable is initialized with all zeros, by default, and its scope is set to within the calling process. For inter-process syn-
chronization, a condition variable must be initialized once, and only once, before use.
A condition variable must not be simultaneously initialized by multiple threads or re-initialized while in use by other threads.
Condition variables attributes may be set to the default or customized at initialization. POSIX threads even allow the default values to
be customized. Establishing these attributes varies depending upon whether POSIX or Solaris threads are used. Similar to the distinctions
between POSIX and Solaris thread creation, POSIX condition variables implement the default, intra-process, unless an attribute object is
modified for inter-process prior to the initialization of the condition variable. Solaris condition variables also implement as the
default, intra-process; however, they set this attribute according to the argument, type, passed to their initialization function.
Condition Wait
The condition wait interface allows a thread to wait for a condition and atomically release the associated mutex that it needs to hold to
check the condition. The thread waits for another thread to make the condition true and that thread's resulting call to signal and wakeup
the waiting thread.
Condition Signaling
A condition signal allows a thread to unblock the next thread waiting on the condition variable, whereas, a condition broadcast allows a
thread to unblock all threads waiting on the condition variable.
Destroy
The condition destroy functions destroy any state, but not the space, associated with the condition variable.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
SEE ALSO fork(2), mmap(2), setitimer(2), shmop(2), cond_broadcast(3C), cond_destroy(3C), cond_init(3C), cond_signal(3C), cond_timedwait(3C),
cond_wait(3C), pthread_cond_broadcast(3C), pthread_cond_destroy(3C), pthread_cond_init(3C), pthread_cond_signal(3C), pthread_cond_timed-
wait(3C), pthread_cond_wait(3C), pthread_condattr_init(3C), signal(3C), attributes(5), mutex(5), standards(5)NOTES
If more than one thread is blocked on a condition variable, the order in which threads are unblocked is determined by the scheduling pol-
icy.
USYNC_THREAD does not support multiple mapplings to the same logical synch object. If you need to mmap() a synch object to different loca-
tions within the same address space, then the synch object should be initialized as a shared object USYNC_PROCESS for Solaris, and
PTHREAD_PROCESS_PRIVATE for POSIX.
SunOS 5.10 20 Jul 1998 condition(5)