lldb / Xcode：如何打印线程索引，ID或名称？

Question

Problem: I want to trace a program with the help of breakpoints with action in Xcode, so what I am interested in is if my function is always executed in one thread.

There is a manual: http://lldb.llvm.org/formats.html which has all the required variables but they don't work for some reason with p/expr commands.

So I'd want something like p ${thread.id} or expr -- thread.id but I've had no luck with them.

The method I know is bad is:

p/x (long)pthread_self()

and to get name:

p new char[256] //it will return suitable pointer like $3 = 0x000000007480840

p (int)pthread_getname_np( (pthread_t)yourId, $3, (size_t)256 ) //it writes thread name to the buffer

p $3 //you will see its name

p delete $3 //if you worry about memory leak

but it looks rather a bad workaround, and doesn't fit well for breakpoints.

Answer 1

The formats mentioned in the "formats.html" page are used not for expressions, but for the way that the thread and frame info is printed whenever lldb prints it. For instance, I have this:

    settings set thread-format thread #${thread.index}: tid = ${thread.id}{, name = ${thread.name}}{, function: ${function.name}} {, stop reason = ${thread.stop-reason}}{, return = ${thread.return-value}}\n

in my .lldbinit, so I can see the thread ID & name when I stop.

If you are running in Xcode, you won't generally see the thread info printed at stop, because Xcode doesn't echo every stop to the Xcode console. But you can still call up some of this information with the "thread info" command:

    (lldb) thread info
    thread #1: tid = 0x34ca69, name = A_Cool_Thread, function: -[SKTGraphicView alignLeftEdges:] , stop reason = breakpoint 2.1

So for your purposes, you can put a breakpoint command on the breakpoints you care about, and have the command be "thread info". Then every stop will show you the ID and the name, among other things.

Note, another way to do the same thing would be to use Python breakpoint commands, for instance:

(lldb) breakpoint command add -s python <BPNO>
Enter your Python command(s). Type 'DONE' to end.
def function (frame, bp_loc, internal_dict):
    """frame: the lldb.SBFrame for the location at which you stopped
       bp_loc: an lldb.SBBreakpointLocation for the breakpoint location information
       internal_dict: an LLDB support object not to be used"""
    print "Thread ID is: ", frame.thread.GetThreadID(), " and name: ", frame.thread.GetName() 
    DONE
(lldb)

Then every time you hit breakpoint you'll see something like:

Thread id is:  3459689  and name:  A_Cool_Thread

BTW, you didn't say what system you were on, but on Mac OS X the thread ID that is listed here is not the pthread ID. The pthread id is only guaranteed to be unique for all the threads that exist at a given time in the program, so while every thread in the program at a given time will have different pthread ID's, there's no guarantee that two threads at different times will have different pthread ID's. Mac OS X has a "globally unique thread ID", however, which is unique across the running of the program. That's what this thread ID is.