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Top Forums Programming Count Number Of Threads in a Process Post 33292 by S.P.Prasad on Thursday 26th of December 2002 04:12:09 AM
Old 12-26-2002
The size of the LWP pool has a critical impact on the performance of the many-to-many model: if the number of LWPs in the pool is nearly equal to the number of threads, the implementation will act much like the one-to-one model. Conversely, if there are very few LWPs in the pool, the implementation will act like the many-to-one model.
Of particular concern is the risk of deadlock with an excessively small pool: one thread may block on a resource in the kernel and go to sleep, and by so doing block the LWP needed to run the resource-holder. To solve this problem, the threads package makes a minimal guarantee to the threads programmer: progress will always be made. This is implemented through the use of the SIGWAITING signal. When the kernel realizes that all of a process's LWPs are blocked at the kernel level, it drops a SIGWAITING on the process. Upon receipt of the signal, the user-level threads package decides whether or not to create a new LWP, on the basis of the number of runnable threads. The SIGWAITING mechanism makes no guarantees about optimal use of LWPs on a multiprocessor. Specifically, a process may have many more runnable user-level threads than it has LWPs, but it does not receive a SIGWAITING until all LWPs are blocked. Thus, even if there are processors available and work to be done, the SIGWAITING mechanism does not guarantee that there is a sufficient number of LWPs to run the user threads on the available processors. If the programmer wishes to use unbound threads and take advantage of all available processors, he or she is required to advise the library on the number of LWPs required.
 

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pbind(1M)						  System Administration Commands						 pbind(1M)

NAME
pbind - control and query bindings of processes or LWPs SYNOPSIS
pbind -b processor_id pid [/lwpid]... pbind [-q] [pid [/lwpid]...] pbind -Q [processor_id...] pbind -u pid [/lwpid]... pbind -U [processor_id...] DESCRIPTION
pbind controls and queries bindings of processes and LWPs (lightweight processes) to processors. pbind can also remove processor bindings that were previously established. When an LWP is bound to a processor, it will be executed only by that processor except when the LWP requires a resource that is provided only by another processor. The binding is not exclusive, that is, the processor is free execute other LWPs as well. Bindings are inherited, so new LWPs and processes created by a bound LWP will have the same binding. Binding an interactive shell to a pro- cessor, for example, binds all commands executed by the shell. Superusers may bind or unbind any process or LWP, while other users can bind or unbind any process or LWP for which they have permission to signal, that is, any process that has the same effective user ID as the user. OPTIONS
The following options are supported: -b processor_id Binds all or a subset of the LWPs of the specified processes to the processor processor_id. Specify processor_id as the processor ID of the processor to be controlled or queried. processor_id must be present and on-line. Use the psrinfo command to determine whether or not processor_id is present and on-line. See psrinfo(1M). -q Displays the bindings of the specified processes or of all processes. If a process is composed of multiple LWPs which have different bindings and the LWPs are not explicitly specified, the bindings of only one of the bound LWPs will be displayed. The bindings of a subset of LWPs can be displayed by appending "/lwpids" to the process IDs. Multiple LWPs may be selected using "-" and "," delimiters. See EXAMPLES. -Q Displays the LWPs bound to the specified list of processors, or all LWPs with processor bindings. For processes composed of multiple LWPs, the bindings of individual LWPs will be displayed. -u Removes the bindings of all or a subset of the LWPs of the specified processes, allowing them to be executed on any on-line processor. -U Removes the bindings of all LWPs bound to the specified list of processors, or to any processor if no argument is specified. OPERANDS
The following operands are supported: pid The process ID of the process to be controlled or queried. lwpid The set of LWP IDs of the specified process to be controlled or queried. The syntax for selecting LWP IDs is as follows: 2,3,4-8 LWP IDs 2, 3, and 4 through 8 -4 LWPs whose IDs are 4 or below 4- LWPs whose IDs are 4 or above processor_id The processor ID of the processor to be controlled or queried. EXAMPLES
Example 1: Binding Processes The following example binds processes 204 and 223 to processor 2: example% pbind -b 2 204 223 process id 204: was 2, now 2 process id 223: was 3, now 2 Example 2: Unbinding a Process The following example unbinds process 204: example% pbind -u 204 Example 3: Querying Bindings The following example queries bindings. It demonstrates that process 1 is bound to processor 0, process 149 has at least one LWP bound to CPU3, and process 101 has no bound LWPs. example% pbind -q 1 149 101 process id 1: 0 process id 149: 3 process id 101: not bound Example 4: Querying LWP Bindings The following example queries bindings of LWPs. It demonstrates that LWP 1 of process 149 is bound to CPU3, and LWP 2 of process 149 is not bound. example% pbind -q 149/1-2 lwp id 149/1: 3 lwp id 149/2: not bound Example 5: Querying LWP Bindings for Processor 2: The following example queries all LWPs bound to processor 2: example% pbind -Q 2 lwp id 149/4: 2 lwp id 149/5: 2 ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ EXIT STATUS
The following exit values are returned: 0 Successful completion. >0 An error occurred. SEE ALSO
psradm(1M), psrinfo(1M), psrset(1M), processor_bind(2), processor_info(2), sysconf(3C), attributes(5) DIAGNOSTICS
pbind: cannot query pid 31: No suchprocess The process specified did not exist or has exited. pbind: cannot bind pid 31: Not owner The user does not have permission to bind the process. pbind: cannot bind pid 31: Invalid argument The specified processor is not on-line. SunOS 5.10 18 July 2004 pbind(1M)
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