How to print pthread t

Question

Searched  but don t come across a satisfying answer    I know there s no a portable way to print a pthread t    How do you do it in your app   Update    Actually I don t need pthread t  but some small numeric id  identifying in debug message different threads    On my system  64 bit RHEL 5 3  it s defined as unsigned long int  so it s big number and just printing it eats a valuable place in debug line  How does gdb assign short tids

User · Answer

GDB uses the thread-id  aka kernel pid  aka LWP  for short numbers on Linux  Try      include  lt syscall h gt             printf  tid    d n   syscall SYS gettid

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if pthread t is just a number  this would be the easiest   int get tid pthread t tid        assert fatal sizeof int   gt   sizeof pthread t         int   threadid    int     void     amp tid      return  threadid

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You could try converting it to an unsigned short and then print just the last four hex digits  The resulting value might be unique enough for your needs

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In this case  it depends on the operating system  since the POSIX standard no longer requires pthread t to be an arithmetic type      IEEE Std 1003 1-2001 Cor 2-2004  item XBD TC2 D6 26 is applied  adding pthread t to the list of types that are not required to be arithmetic types  thus allowing pthread t to be defined as a structure    You will need to look in your sys types h header and see how pthread t is implemented  then you can print it how you see fit   Since there isn t a portable way to do this and you don t say what operating system you are using  there s not a whole lot more to say   Edit  to answer your new question  GDB assigns its own thread ids each time a new thread starts      For debugging purposes  gdb associates its own thread number   always a single integer   with each thread in your program     If you are looking at printing a unique number inside of each thread  your cleanest option would probably be to tell each thread what number to use when you start it

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A lookup table  pthread t   int  could become a memory leak in programs that start a lot of short-lived threads   Creating a hash of the bytes of the pthread t  whether it be structure or pointer or long integer or whatever  may be a usable solution that doesn t require lookup tables   As with any hash there is a risk of collisions  but you could tune the length of the hash to suit your requirements

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I know  this thread is very old  Having read all above posts  I would like to add one more idea to handle this in a neat way  If you get into the mapping business anyway  mapping pthread to to an int   you could as well go one step further in readability  Make your pthread create wrapper such that it takes a string  too   the name of the thread   I learned to appreciate this  SetThreadName    feature on windows and windows CE   Advantages  Your ids are not just numbers but you also see  which of your threads has which purpose

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This will print out a hexadecimal representation of a pthread t  no matter what that actually is   void fprintPt FILE  f  pthread t pt      unsigned char  ptc    unsigned char   void    amp pt     fprintf f   0x      for  size t i 0  i lt sizeof pt   i          fprintf f    02x    unsigned  ptc i             To just print a small id for a each pthread t something like this could be used  this time using iostreams    void printPt std  ostream  amp strm  pthread t pt      static int nextindex   0    static std  map lt pthread t  int gt  ids    if  ids find pt     ids end          ids pt    nextindex          strm  lt  lt  ids pt       Depending on the platform and the actual representation of pthread t it might here be necessary to define an operator lt  for pthread t  because std  map needs an ordering on the elements   bool operator lt  const pthread t  amp left  const pthread t  amp right

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Just a supplement to the first post  use a user defined union type to store the pthread t   union tid       pthread t pthread id      unsigned long converted id       Whenever you want to print pthread t  create a tid and assign tid pthread id        then print tid converted id

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On Centos 5 4 x86 64  pthread t is a typedef to a unsigned long   Therefore  we could do this      include  lt iostream gt   include  lt pthread h gt   int main         pthread t x      printf   li n    unsigned long int  x       std  cout  lt  lt   unsigned long int  x  lt  lt    n

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No need to get fancy  you can treat pthread t as a pointer without a cast  printf  quot awesome worker thread id  p n quot   awesome worker thread id    Output   awesome worker thread id 0x6000485e0

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OK  seems this is my final answer  We have 2 actual problems    How to get shorter unique IDs for thread for logging  Anyway we need to print real pthread t ID for thread  just to link to POSIX values at least     1  Print POSIX ID  pthread t   You can simply treat pthread t as array of bytes with hex digits printed for each byte  So you aren t limited by some fixed size type  The only issue is byte order  You probably like if order of your printed bytes is the same as for simple  int  printed  Here is example for little-endian and only order should be reverted  under define   for big-endian    include  lt pthread h gt   include  lt stdio h gt   void print thread id pthread t id        size t i      for  i   sizeof i   i  --i          printf   02x       unsigned char    amp id    i - 1       int main         pthread t id   pthread self         printf   08x n   id       print thread id id        return 0      2  Get shorter printable thread ID  In any of proposed cases you should translate real thread ID  posix  to index of some table  But there is 2 significantly different approaches   2 1  Track threads   You may track threads ID of all the existing threads in table  their pthread create   calls should be wrapped  and have  overloaded  id function that get you just table index  not real thread ID  This scheme is also very useful for any internal thread-related debug an resources tracking  Obvious advantage is side effect of thread-level trace   debug facility with future extension possible  Disadvantage is requirement to track any thread creation   destruction   Here is partial pseudocode example   pthread create wrapper           id   pthread create         add thread id      pthread destruction wrapper           Main problem is it should be called        pthread cleanup     calls are possible solution        remove thread pthread self        unsigned thread id pthread t known pthread id      return seatch thread index known pthread id         user code    printf  04x   thread id pthread self        2 2  Just register new thread ID   During logging call pthread self   and search internal table if it know thread  If thread with such ID was created its index is used  or re-used from previously thread  actually it doesn t matter as there are no 2 same IDs for the same moment   If thread ID is not known yet  new entry is created so new index is generated   used   Advantage is simplicity  Disadvantage is no tracking of thread creation   destruction  So to track this some external mechanics is required

User · Answer

As James mentioned above  the best way is to look at the header where the type is defined    You can find the definition of pthread t in pthreadtypes h which can be found at       usr include bits pthreadtypes h

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You could do something like this   int thread counter   0  pthread mutex t thread counter lock   PTHREAD MUTEX INITIALIZER   int new thread id         int rv      pthread mutex lock  amp thread counter lock       rv     thread counter      pthread mutex unlock  amp thread counter lock       return rv     static void  threadproc void  data        int thread id   new thread id        printf  Thread  d reporting for duty  n   thread id       return NULL      If you can rely on having GCC  clang also works in this case   you can also do this   int thread counter   0   static void  threadproc void  data        int thread id     sync add and fetch  amp thread counter  1       printf  Thread  d reporting for duty  n   thread id       return NULL      If your platform supports this  a similar option   int thread counter   0  int   thread thread id   0   static void  threadproc void  data        thread id     sync add and fetch  amp thread counter  1       printf  Thread  d reporting for duty  n   thread id       return NULL      This has the advantage that you don t have to pass around thread id in function calls  but it doesn t work e g  on Mac OS

[c++] How to print pthread_t

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