.PB - Display Blocked Thread Information

Display information about all blocked threads.

Syntax:

────.PB ──────────────────────┬──────────┬────────────────────
                                ├── #    ──┤
                                ├── *    ──┤
                                └── slot ──┘

Parameters:

slot

Display user information for thread slot slot.

The following short-hand may be used for the slot number:

• The current (last) thread the dispatcher gave control to. This value is taken from the word a global label:

       _TaskNumber
  

  
  
• The debugger default thread slot. This defaults to the current slot unless overridden by the .S command.

  If no slot number is given then all thread slots are displayed in slot number order.

Results & Notes:

The .PB command locates each thread's TCB from the thread slot table, the linear address of which is given by global variable:

_papTCBSlots

or by traversing the process tree using TCBpTCBNext (TCB +0x14), TCBpPTDA (TCB +0x08) and ptda_pTCBHead (PTDA + 0x20) fields.

Output is displayed only if a thread is blocked on a Block-Id. It appears in tabular form as follows:

 Slot  Sta BlockID  Name     Type        Addr    Symbol
 0001  blk fff11050 *ager
 0002  blk fff74f59 *tsd                         _tkTSDDaemon
 0003  blk fff43c78 *ctxh                        _kmCTXHDaemon
 0004  blk fff7545a *kdb                         _tkKDBDaemon
 0005  blk fff02dfc *lazyw                       _semLW
 0006  blk fff111d4 *asyncr                      _AsyncReadSem
 0008  blk fffe000e pmshell  RamSem    074b:06d6
 000a  blk ffca0002 pmshell
 000b  blk fffd000b pmshell  MuxWait
 000c  blk fffd000c pmshell  MuxWait
 000d  blk 04000df0 pmshell  DosSem    0400:0df0 CtrlNumLkQ
 0007  blk fe750a10 pmshell  Sem32     8001 0019 vhevLazyWrite
 0010  blk fe728dcc pmshell  Sem32     8001 0001 SrvReq
 0011  blk fffe0006 pmshell  RamSem    d0c7:0020
 0012  blk fffd0012 pmshell  MuxWait
*0013  blk fffe0007 pmshell  RamSem    d09f:0bc0 memory_pool + 127
 0014# blk fffe0008 pmshell  RamSem    d09f:0bc8 memory_pool + 12f

Each of the fields has the following meaning:

slot

The unique (hexadecimal) index in to the thread slot table of all threads.

This value may be flagged with:

• to the left to signify the last dispatched thread.
  
• to the right to signify the Kernel Debugger or Dump Formatter default thread slot.

  Slot may be found in the TCBNumber (TCB + 0x2) field of the TCB

Sta
The ascending or desired state of the thread. This should always appear as blk for the .PB command, however Dump Formatter does not check the thread state so formats all threads. Those whose state is not blk should be ignored. From fix pack 29 for Warp V3 and base Warp V4 this has been fixed so that only blocked threads are formatted. See Scheduler Finite State Machine and .PQ command for more information on thread states.
BlockID
The token used by TKSleep and TKWapeUp to sleep and wake a thread on an event.

The BlockId is taken from TCBSleepID (TCB + 0x18c).

The BlockID is a conventional value. A number of conventions are used by various system components. Usually the BlockID is constructed so to be unique across all conventions. Frequently it will refer to the address of an associated resource, such as a system control block, or a field within a control block. See discussion of the Type field below for more information on interpreting BlockIds.

Name
The name of the primary executable running in this process.

See name field description of the .P command for further information.

Type
Interpretation of the use of the BlockID in conjunction with double word TCB_SemInfo (TCB + 0x14c) and double word TCB_SemDebugAddr (TCB + 0x150).

The following Types are recognised by the Dump Formatter and Kernel Debugger:

RamSem

The thread is waiting on a RamSem or FastSafeRamSem.

The high word of the BlockID is 0xfffe, the low word is the RamSemID taken from the RamSem structure.

The Addr field is taken from TCB_SemInfo. This is a selector:offset address of the RAMSEM The RamSem may be imbedded within a FastSafeRamSem or a PMFastSafeRamSem.

The Symbol displayed is either that of the TCB_SemDebugAddr or if -1, the RamSem address. See LN command for information on displaying symbols.

MuxWait
The thread is waiting on multiple events.

The high word of the BlockID is 0xfffd, the low word is the slot of the waiting thread.

TCB_SemInfo and TCB_SemDebugAddr are not used with a MuxWait BlockID.

To locate the semaphores that comprise a given MuxWait proceed as follows:

• Locate the MuxWait table at symbol MuxTable. Display this using DB for convenience. This table comprises 9 byte entries whose format is given by the MuxTableEntry structure.

• Scan the MuxTable for entries that have this thread's slot number (+0x2 into each entry).

• Of those entries, select those with non-zero MuxType (+4 into each entry).

• Choose one of the following:

  For type 1 (SysSem)

  the last double word is the linear address of a system semaphore structure. Use the technique described below under SysSem for interpreting the SysSem.
  For type 2 (RamSem)
  the last double word of the entry contains the RamSem handle, the high word is the hob of the memory object containing the RamSem. The low word is the offset into the object where the RamSem is located. Use the technique described above under RamSem for interpreting the RamSem
  For type 3 (Physical RamSem)
  the last double word is the physical address of the RamSem.
  For type 4 (32-bit event sem)
  the last double word is the physical address of a 32-bit event semaphore. See Sem32 below.
  See Mux Semaphore example debugging log for an explicit example of using this technique.

  Addr and Symbol fields are blank.

  ReqPkt
  The thread is waiting for an I/O request packed to complete.

  The BlockID is the Selector:Offset address of the request packet. The Selector is the DOSGROUP kernel selector and should be selector 400.

  The address should lie between addresses at global symbols: FirstPacket and LastPacket.

  See the Physical Device Driver Reference manual for information on device driver request packets.

  Addr and Symbol fields are blank.

  SysSem
  The thread is waiting on a system semaphore.

  The BlockID is the Selector:Offset address of the SysSemTblStruc structure. The Selector is the DOSGROUP kernel selector and should be selector 400.

  The address should lie within the System Semaphore Data Table, located at symbol SysSemDataTable for length 256*6 bytes.

  Offset +0 of each table entry contains the owner's thread number.

  The name associated with the semaphore may be located as follows:

  • Locate the SysSem RMP segment by displaying double word at symbol SysSemRMPHdl. The high word is the selector for the semaphore RMP.

  • Display the System Semaphore RMP using DB. The first 0x14 bytes is the RMP header. The remainder comprises variable length records. The first word of each record is its length and therefore the relative offset to the beginning of the following record. Offset 2 of each record is the semaphore data table selector offset.

  • Scan the RMP looking for an offset that matches the low word of the BlockID. When found the remaining bytes of the RMP record is the semaphore name (with the top two bytes overlaid by the semaphore offset).

    See System Semaphore example debugging log for an explicit example of using this technique.

    The Addr and Symbol fields are blank.

  DosSem
  The thread is waiting on an internal RamSem or blocking on an address in the kernel's DOSGROUP segment.

  The BlockID is the selector:offset of the DosSem. The Selector is the DOSGROUP kernel selector and should be selector 400. The offset does not lie in the System Semaphore Data Table or the I/O Request Packet Table.

  Addr is the BlockID formatted as selector:offset.

  The Symbol displayed is either that of the TCB_SemDebugAddr or if -1, the DosSem address. See LN command for information on displaying symbols.

  Sem32
  The thread is waiting on a 32-bit semaphore.

  The BlockID is the address of the 32-bit Semaphore structure.

  TCB_SemInfo contains the semaphore handle. This is of the form:

  8001nnnn

  Shared 32-bit semaphore. nnnn is the (double-word) index into the shared semaphore table located at symbol _pShSemTbl. Each entry is an address of the corresponding 32-bit semaphore structure. (that is, the Sem32 BlockID).
  0001nnnn
  Private 32-bit semaphore. nnnn is the (double-word) index into the private semaphore table located at pPrSemTbl (PTDA +0x4cc (H/R: +0x4c4)). Each entry is an address of the corresponding 32-bit semaphore structure. (that is, the Sem32 BlockID).
  Addr field is the semaphore handle formatted as two words.

  The Symbol displayed is either that of the TCB_SemDebugAddr or if -1, the Sem32 address. See LN command for information on displaying symbols.

  Use the .D SEM32 comand with the BlockID to format the 32-bit semaphore.

  Buffer
  The thread is waiting for a file system buffer.

  The BlockId is the selector:offset address of the buffer. The high word is the buffer selector and should be a8.

  The Addr and Symbol fields are blank.

  SFT
  The thread is waiting for a SFT entry.

  The BlockId is the selector:offset address of the SFT. The high word is the buffer selector and should be one that is listed in the SFT table pointed to by c0:0.

  The Addr and Symbol fields are blank.

  ChildWait
  The thread is waiting in DosWaitChild for a child process to terminate.

  The high word of the BlockID is the ptda_Pid offset from selector 30 (0xffca).

  The low word of the BlockID is the Pid to which this thread belongs.

  blank type
  The thread is waiting on a BlockId that the Kernel Debugger and Dump Formatter have not been able to identify.

  Addr field is blank.

  The Symbol displayed is either that of the TCB_SemDebugAddr or if -1, the Sem32 address. See LN command for information on displaying symbols.

  Notes:

  The BlockID interpretation is not exact. A device driver, for example, could call DevHlp_ProcBlock using a value for BlockID that conflicts with another convention.

  Under the Debug kernel only, TCB_SemDebugAddr is used to record the creator's address of kernel, system and RAM semaphores. If it is not used it is set to 0xffffffff.

  ChildWait BlockIDs might be missed by the Dump Formatter and Kernel Debugger. Look out for BlockIDs of the form 0xffca????. ChildWait is correctly reported from fix pack 29 for Warp V3 and base Warp V4.

  Some Sem32 BlockIDs are missed by the Dump Formatter. Check TCB_SemInfo for a 32-bit semaphore handle and BlockIDs of the form 0xfe??????

  If BlockID is a linear address owned by ksem then the semaphore is a Kernel Semaphore. However, not every KSEM is owned ksem owned memory. Under the ALLSTRICT kernel, a KSEM may be readily identified from the first 4 bytes, which have the signature "KSEM" Under the RETAIL and HSTRICT kernels, the Blockid is chosen to be the address (or handle) of the KSEM. Under the ALLSTRICT kernel, Event KSEMs use the KSEM handle+4 as the BlockId. Use .D KSEM command with the BlockID to format a KSEM.

  In general a BlockID will be chosen to be meaningful to the programs using it. Often it is an address of a resource that needs to be serialised. Where no other information is given one should try:

  • M BlockID
    to try to establish an owner of the resource represented by the BlockID
    LN BlockID
    to try to establish a meaningful symbol associated with the BlockID
    Unwind the User's Stack
    to try to establish the API or call the lead to the thread waiting on the BlockID (see .K command)
    Addr
    The address of the semaphore associated with this BlockID

    See Type field discussion above for more precise information.

    Symbol
    Either the symbolic address of the creator or of the associated semaphore.

    See Type field discussion above for more precise information.

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