Id is the alias name if the option alias(name) is given. Otherwise it is a blob of type thread. The anonymous blobs are subject to atom garbage collection. If a thread handle is garbage collected and the thread is not detached, it is joined if it has already terminated (see thread_join/2) and detached otherwise (see thread_detach/1).^{198Up to version 7.3.23, anonymous thread handles were integers. Using integers did not allow for safe checking of the thread's status as the thread may have died and the handle may have been reused and did not allow for garbage collection to take care of forgotten threads.} The thread identifier blobs are printed as <thread>(I,Ptr), where I is the internal thread identifier and Ptr is the unique address of the identifier. The I is accepted as input argument for all thread APIs that accept a thread identifier for convenient interaction from the toplevel. See also thread_property/2.

Options is a list of options. The currently defined options are below. Stack size options can also take the value inf or infinite, which is mapped to the maximum stack size supported by the platform.

affinity(+CpuSet)

Specify that the thread should only run on the specified CPUs (cores). CpuSet is a list of integers between 0 (zero) and the known number of CPUs (see cpu_count). If CpuSet is empty a domain_error is raised. Referring to CPUs equal to or higher than the known number of CPUs returns an existence_error.

This option is currently implemented for systems that provide pthread_attr_setaffinity_np(). The option is silently ignored on other systems.^{bugThere is currently no way to discover whether this option is supported.}

alias(AliasName)

Associate an‘alias name’with the thread. This name may be used to refer to the thread and remains valid until the thread is joined (see thread_join/2). If the OS supports it (e.g., Linux), the operating system thread is named as well.

at_exit(:AtExit)

Register AtExit as using thread_at_exit/1 before entering the thread goal. Unlike calling thread_at_exit/1 as part of the normal Goal, this ensures the AtExit is called. Using thread_at_exit/1, the thread may be signalled or run out of resources before thread_at_exit/1 is reached. See thread_at_exit/1 for details.

debug(+Bool)

Enable/disable debugging the new thread. If false (default true), the new thread is created with the property debug(false) and debugging is disabled before the new thread is started. The thread debugging predicates such as tspy/1 and tdebug/0 do not signal threads with the debug property set to false.^{199Currently, the flag is only used as a hint for the various debugging primitives, i.e., the system does not really enforce that the target thread stays in nodebug mode.}

detached(Bool)

If false (default), the thread can be waited for using thread_join/2. thread_join/2 must be called on this thread to reclaim all resources associated with the thread. If true, the system will reclaim all associated resources automatically after the thread finishes. Please note that thread identifiers are freed for reuse after a detached thread finishes or a normal thread has been joined. See also thread_join/2 and thread_detach/1.

If a detached thread dies due to failure or exception of the initial goal, the thread prints a message using print_message/2. If such termination is considered normal, the code must be wrapped using ignore/1 and/or catch/3 to ensure successful completion.

inherit_from(+ThreadId)

Inherit defaults from the given ThreadId instead of the calling thread. This option was added to ensure that the __thread_pool_manager (see thread_create_in_pool/4), which is created lazily, has a predictable state. The following properties are inherited:

• The prompt (see prompt/2)
• The typein module (see module/1)
• The standard streams (user_input, etc.).
• current_input and current_output are bound to user_input and user_output.
• The default encoding (see encoding)
• The default locale (see set_locale/1)
• All prolog flags
• The stack limit (see Prolog flag stack_limit).

queue_max_size(Size)

Enforces a maximum to the number of terms in the input queue. See message_queue_create/2 with the max_size(o)ption for details.

stack_limit(Bytes)

Set the size limit for the Prolog stacks. See the Prolog flag stack_limit. The default is inherited from the calling thread or the thread specified using inherit_from(ThreadId).

c_stack(Bytes)

Set the limit to which the C stack of this thread may grow. The default, minimum and maximum values are system-dependent. The value is rounded up to the system page size and SWI-Prolog enforces a minimum of 64 K-bytes.

The Goal argument is copied to the new Prolog engine. This implies that further instantiation of this term in either thread does not have consequences for the other thread: Prolog threads do not share data from their stacks.