- Reference manual
- The SWI-Prolog library
- library(aggregate): Aggregation operators on backtrackable predicates
- library(apply): Apply predicates on a list
- library(assoc): Association lists
- library(broadcast): Broadcast and receive event notifications
- library(charsio): I/O on Lists of Character Codes
- library(check): Consistency checking
- library(clpb): CLP(B): Constraint Logic Programming over Boolean Variables
- library(clpfd): CLP(FD): Constraint Logic Programming over Finite Domains
- library(clpqr): Constraint Logic Programming over Rationals and Reals
- library(csv): Process CSV (Comma-Separated Values) data
- library(debug): Print debug messages and test assertions
- library(error): Error generating support
- library(gensym): Generate unique identifiers
- library(iostream): Utilities to deal with streams
- library(lists): List Manipulation
- library(main): Provide entry point for scripts
- library(nb_set): Non-backtrackable set
- library(www_browser): Activating your Web-browser
- library(option): Option list processing
- library(optparse): command line parsing
- library(ordsets): Ordered set manipulation
- library(pairs): Operations on key-value lists
- library(persistency): Provide persistent dynamic predicates
- library(pio): Pure I/O
- library(predicate_options): Declare option-processing of predicates
- library(prolog_pack): A package manager for Prolog
- library(prolog_xref): Cross-reference data collection library
- library(quasi_quotations): Define Quasi Quotation syntax
- library(random): Random numbers
- library(readutil): Reading lines, streams and files
- library(record): Access named fields in a term
- library(registry): Manipulating the Windows registry
- library(simplex): Solve linear programming problems
- library(solution_sequences): Modify solution sequences
- library(tabling): Tabled execution (SLG)
- library(thread_pool): Resource bounded thread management
- library(ugraphs): Unweighted Graphs
- library(url): Analysing and constructing URL
- library(varnumbers): Utilities for numbered terms
- library(yall): Lambda expressions
- The SWI-Prolog library
- Reference manual
library(thread_pool) manages threads in
pools. A pool defines properties of its member threads and the maximum
number of threads that can coexist in the pool. The call thread_create_in_pool/4
allocates a thread in the pool, just like thread_create/3.
If the pool is fully allocated it can be asked to wait or raise an
The library has been designed to deal with server applications that receive a variety of requests, such as HTTP servers. Simply starting a thread for each request is a bit too simple minded for such servers:
- Creating many CPU intensive threads often leads to a slow-down rather than a speedup.
- Creating many memory intensive threads may exhaust resources
- Tasks that require little CPU and memory but take long waiting for external resources can run many threads.
Using this library, one can define a pool for each set of tasks with comparable characteristics and create threads in this pool. Unlike the worker-pool model, threads are not started immediately. Depending on the design, both approaches can be attractive.
The library is implemented by means of a manager thread with the
fixed thread id
__thread_pool_manager. All state is
maintained in this manager thread, which receives and processes requests
to create and destroy pools, create threads in a pool and handle
messages from terminated threads. Thread pools are not saved in a
saved state and must therefore be recreated using the initialization/1
directive or otherwise during startup of the application.
- [det]thread_pool_create(+Pool, +Size, +Options)
- Create a pool of threads. A pool of threads is a declaration for
creating threads with shared properties (stack sizes) and a limited
number of threads. Threads are created using
If all threads in the pool are in use, the behaviour depends on the
waitoption of thread_create_in_pool/4 and the
backlogoption described below. Options are passed to thread_create/3, except for
- Maximum number of requests that can be suspended. Default is
infinite. Otherwise it must be a non-negative integer. Using
backlog(0)will never delay thread creation for this pool.
The pooling mechanism does not interact with the
detachedstate of a thread. Threads can be created both
detachedand normal and must be joined using thread_join/2 if they are not detached.
- Destroy the thread pool named Name.
- True if Name refers to a defined thread pool.
- [nondet]thread_pool_property(?Name, ?Property)
- True if Property is a property of thread pool Name.
Defined properties are:
- Thread creation options for this pool
- Number of free slots on this pool
- Total number of slots on this pool
- ListOfIDs is the list or threads running in this pool
- Number of running threads in this pool
- Number of delayed thread creations on this pool
- [det]thread_create_in_pool(+Pool, :Goal, -Id, +Options)
- Create a thread in Pool. Options overrule default
thread creation options associated to the pool. In addition, the
following option is defined:
true(default) and the pool is full, wait until a member of the pool completes. If
false, throw a resource_error.
resource_error(threads_in_pool(Pool))is raised if wait is
falseor the backlog limit has been reached.
existence_error(thread_pool, Pool)if Pool does not exist.
- Hook to create a thread pool lazily. The hook is called if
discovers that the thread pool does not exist. If the hook succeeds, thread_create_in_pool/4
retries creating the thread. For example, we can use the following
declaration to create threads in the pool
media, which holds a maximum of 20 threads.
:- multifile thread_pool:create_pool/1. thread_pool:create_pool(media) :- thread_pool_create(media, 20, ).