12-24-2002
I don't exactly have an answer, but I may be able to shed some light here.
When you use fopen(), you get a stream. But this is built on open() and open() would give you an fd. The fd is a kernel thing and the stream is a library thing built on top on it.
In the same way, a lwp is a kernel thing and a thread (or a pthread) is a library thing.
What I have just discovered this morning is that the lwp's and the threads are not in a one-to-one correspondence.
Look at "man pthread_attr_init". You will see language like 'This thread is not "bound" to a LWP, and is also called an unbound thread.'
I gotta read up on threads sometimes. Since you are trying to count them, maybe you should do the same. In any event, it looks like counting LWP's is not going to help you counting threads.
Here is my guess as to why 3 lwps:
Consider what would happen if you did an fopen(), but all of the fd's were in use. If you had not yet reached the limit on fd's, when the open() system call occurred, the kernel would allocate another chunk of fd's to the process, not just one.
Or if you need more stack, your stack grows by a page, not just the few bytes that you need.
Or if you write another byte to a disk file, the file may grow by a full block.
The kernel may not be easily able to give you just one lwp, or it may just be attempting to be efficient.
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LEARN ABOUT HPUX
pthread_condattr_getpshared
pthread_condattr_getpshared(3T) pthread_condattr_getpshared(3T)
NAME
pthread_condattr_getpshared(), pthread_condattr_setpshared() - get or set the process-shared attribute
SYNOPSIS
PARAMETERS
attr Pointer to the condition variable attributes object whose process-shared attribute is to be set/retrieved.
pshared This parameter either specifies the new value of the process-shared attribute (set function) or it points to the memory
location where the process-shared attribute of attr is to be returned (get function).
DESCRIPTION
The attributes object attr must have been previously initialized with the function before these functions are called.
The functions are used to set and retrieve the process-shared attribute in a condition variable attributes object. The legal values for
the process-shared attribute are:
This option permits a condition variable to be operated upon by any thread
that has access to the memory where the condition variable is allocated. The application is responsible for allocating the
condition variable in memory that multiple processes can access.
The condition variable can be operated on only by threads created within
the same process as the thread that initialized the condition variable. If threads of differing processes attempt to operate
on such condition variable, the behavior is undefined.
The default value of process-shared is
sets the process-shared attribute in attr. The new value of the process-shared attribute of attr is set to the value specified in the
pshared parameter.
retrieves the value of the process-shared attribute from attr. The value of the process-shared attribute of attr is returned in the
pshared parameter.
RETURN VALUE
Upon successful completion, and return zero. Otherwise, an error number is returned to indicate the error (the variable is not set).
ERRORS
If any of the following occur, the and functions return the corresponding error number:
is not defined and these functions are not supported.
For each of the following conditions, if the condition is detected, the function returns the corresponding error number:
attr is not a valid condition variable attributes object.
The value specified by
pshared is not a legal value.
For each of the following conditions, if the condition is detected, the function returns the corresponding error number:
The value specified by
attr or pshared is invalid.
WARNINGS
If a condition variable is created with the process-shared attribute defined as the cooperating processes should have access to the memory
in which the condition variable is allocated.
AUTHOR
and were derived from the IEEE POSIX P1003.1c standard.
SEE ALSO
pthread_create(3T), pthread_condattr_init(3T), pthread_cond_init(3T), pthread_mutex_init(3T).
STANDARDS CONFORMANCE
Pthread Library pthread_condattr_getpshared(3T)