.. mode: -*- rst -*- Thread Manager ============== :Tag: design.mps.thread-manager :Author: Richard Brooksby :Date: 1995-11-20 :Status: incomplete design :Revision: $Id: //info.ravenbrook.com/project/mps/version/1.113/design/thread-manager.txt#1 $ :Copyright: See `Copyright and License`_. :Index terms: pair: thread manager; design Purpose ------- The Thread Manager handles various thread-related functions required by the MPS. These are: - stack scanning; - suspension and resumption of the mutator threads. Context ------- The barrier requires suspension and resumption of threads in order to ensure that the collector has exclusive access to part of memory. [design.mps.barrier.@@@@] Stack scanning is provided as a service to the client. [Link?@@@@] Overview -------- ``typedef struct mps_thr_s *Thread`` Each thread is represented by an object of type ``Thread``. The ``Thread`` type is implemented as an ADT. A list of ``Thread`` objects is maintained in the arena (as the ``Ring`` structure ``arena->threadRing``). The ``Thread`` object contains operating-system-dependent information about the thread -- information necessary for manipulating the thread and for scanning the thread context. Thread "registration" adds or removes the current thread to the ``Thread`` list in the arena. Detailed Design --------------- Stack scan .......... This is a module providing a stack scanning function. The scanning is architecture and operating system dependent. Typically the function will push the subste of the save registers (those preserved across function calls) which may contain pointers (that is, neither floating-point or debugging registers) and call ``TraceScanStack()`` on the appropriate range. Thread interface ................ ``Res ThreadRegister(Thread *threadReturn, Arena arena)`` Register the current thread with the arena, allocating a new ``*threadReturn`` to point to it. ``void ThreadDeregister(Thread thread, Arena arena)`` Remove ``thread`` from the list of threads managed by the arena and free it. ``void ThreadRingSuspend(Ring threadRing)`` Suspend all the threads on the list ``threadRing``, except for the current thread. ``void ThreadRingResume(Ring threadRing)`` Resume all the threads on the list ``threadRing``. ``Res ThreadScan(ScanState ss, Thread thread, void *stackBot)`` Scan the stacks and root registers of ``thread``, treating each value found as an ambiguous reference. The exact definition is operating system and architecture dependent Single-threaded generic implementation ...................................... In ``than.c``. - Single threaded (calling ``ThreadRegister()`` on a second thread causes an assertion failure). - ``ThreadRingSuspend()`` and ``ThreadRingResume()`` do nothing because there are no other threads. - ``ThreadScan()`` calls ``StackScan()``. POSIX threads implementation ............................ In ``thix.c``. See design.mps.pthreadext. Win32 implementation .................... In ``thw3.c``. - Supports multiple threads. - Structured exception style faults are expected. - ``ThreadRingSuspend()`` and ``ThreadRingResume()`` loop over threads and call Win32 API functions ``SuspendThread()`` and ``ResumeThread()``. - ``ThreadRegister()`` records information for the current thread: - A Win32 "handle" with access flags ``THREAD_SUSPEND_RESUME`` and ``THREAD_GET_CONTEXT``. This handle is needed as parameter to ``SuspendThread()`` and ``ResumeThread()``. - The Win32 ``GetCurrentThreadId()`` so that the current thread may be identified. - Stack scanning is Win32 specific: - ``ThreadScan()`` calls ``StackScan()`` if the thread is current. ``GetThreadContext()`` doesn't work on the current thread (the context would not necessarily have the values which were in the saved registers on entry to the MM). - Otherwise it calls ``GetThreadContext()`` to get the root registers and the stack pointer. - The thread's registers are dumped into a ``CONTEXT`` structure and fixed in memory. - Scan the stack (getting the stack pointer from ``CONTEXT.Rsp``). Issues ------ #. Scanning after exceptions. ``StackScan()`` relies on the non-preserved registers having been pushed on the stack. If we want to scan after a fault we must make sure that these registers are either already stored on the stack, or, have an extra function to do this explicitly. #. Multiple registration. It is not clear whether a thread should be allowed to be registered multiple times. We do not provide a mechanism for knowing whether a thread is already registered with an arena. Document History ---------------- - 1995-11-20 RB_ Incomplete design. - 2002-06-21 RB_ Converted from MMInfo database design document. - 2013-05-26 GDR_ Converted to reStructuredText. .. _RB: http://www.ravenbrook.com/consultants/rb/ .. _GDR: http://www.ravenbrook.com/consultants/gdr/ Copyright and License --------------------- Copyright © 2013-2014 Ravenbrook Limited. All rights reserved. . This is an open source license. Contact Ravenbrook for commercial licensing options. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: #. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. #. 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