Simple example of threading in C

Question

Can someone post a simple example of starting two  Object Oriented  threads in C      I m looking for actual C   thread objects that I can extend run methods on  or something similar  as opposed to calling a C-style thread library   I left out any OS specific requests in the hopes that whoever replied would reply with cross platform libraries to use  I m just making that explicit now

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When searching for an example of a C   class that calls one of its own instance methods in a new thread  this question comes up  but we were not able to use any of these answers that way  Here s an example that does that   Class h  class DataManager   public      bool hasData      void getData        bool dataAvailable         Class cpp   include  DataManager h   void DataManager  getData            perform background data munging     hasData   true         be sure to notify on the main thread    bool DataManager  dataAvailable         if  hasData                return true            else               std  thread t  amp DataManager  getData  this           t detach       as opposed to  join  which runs on the current thread           Note that this example doesn t get into mutex or locking

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Unless one want a separate function in global namespacs  we can use lambda functions for creating threads  One of the major advantage of creating thread using lambda is that we don t need to pass local parameters as an argument list  We can use capture list for the same and the closure property of lambda will take care of the lifecycle  Here is a sample code int main         int localVariable   100       thread th                  cout lt  lt  quot The Value of local variable   gt   quot  lt  lt localVariable lt  lt endl               th join         return 0     By far  I ve found C   lambdas to be the best way of creating threads especially for simpler thread functions

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Well  technically any such object will wind up being built over a C-style thread library because C   only just specified a stock std  thread model in c  0x  which was just nailed down and hasn t yet been implemented  The problem is somewhat systemic  technically the existing c   memory model isn t strict enough to allow for well defined semantics for all of the  happens before  cases  Hans Boehm wrote an paper on the topic a while back and was instrumental in hammering out the c  0x standard on the topic   http   www hpl hp com techreports 2004 HPL-2004-209 html  That said there are several cross-platform thread C   libraries that work just fine in practice  Intel thread building blocks contains a tbb  thread object that closely approximates the c  0x standard and Boost has a boost  thread library that does the same   http   www threadingbuildingblocks org   http   www boost org doc libs 1 37 0 doc html thread html  Using boost  thread you d get something like    include  lt boost thread hpp gt   void task1             do stuff    void task2             do stuff    int main  int argc  char    argv        using namespace boost       thread thread 1   thread task1       thread thread 2   thread task2           do other stuff     thread 2 join        thread 1 join        return 0

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Well  technically any such object will wind up being built over a C-style thread library because C   only just specified a stock std  thread model in c  0x  which was just nailed down and hasn t yet been implemented  The problem is somewhat systemic  technically the existing c   memory model isn t strict enough to allow for well defined semantics for all of the  happens before  cases  Hans Boehm wrote an paper on the topic a while back and was instrumental in hammering out the c  0x standard on the topic   http   www hpl hp com techreports 2004 HPL-2004-209 html  That said there are several cross-platform thread C   libraries that work just fine in practice  Intel thread building blocks contains a tbb  thread object that closely approximates the c  0x standard and Boost has a boost  thread library that does the same   http   www threadingbuildingblocks org   http   www boost org doc libs 1 37 0 doc html thread html  Using boost  thread you d get something like    include  lt boost thread hpp gt   void task1             do stuff    void task2             do stuff    int main  int argc  char    argv        using namespace boost       thread thread 1   thread task1       thread thread 2   thread task2           do other stuff     thread 2 join        thread 1 join        return 0

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Create a function that you want the thread to execute  eg   void task1 std  string msg        std  cout  lt  lt   task1 says     lt  lt  msg      Now create the thread object that will ultimately invoke the function above like so   std  thread t1 task1   Hello       You need to  include  lt thread gt  to access the std  thread class   The constructor s arguments are the function the thread will execute  followed by the function s parameters  The thread is automatically started upon construction   If later on you want to wait for the thread to be done executing the function  call   t1 join        Joining means that the thread who invoked the new thread will wait for the new thread to finish execution  before it will continue its own execution      The Code   include  lt string gt   include  lt iostream gt   include  lt thread gt   using namespace std      The function we want to execute on the new thread  void task1 string msg        cout  lt  lt   task1 says     lt  lt  msg     int main            Constructs the new thread and runs it  Does not block execution      thread t1 task1   Hello            Do other things            Makes the main thread wait for the new thread to finish execution  therefore blocks its own execution      t1 join        More information about std  thread here   On GCC  compile with -std c  0x -pthread  This should work for any operating-system  granted your compiler supports this  C  11  feature

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Well  technically any such object will wind up being built over a C-style thread library because C   only just specified a stock std  thread model in c  0x  which was just nailed down and hasn t yet been implemented  The problem is somewhat systemic  technically the existing c   memory model isn t strict enough to allow for well defined semantics for all of the  happens before  cases  Hans Boehm wrote an paper on the topic a while back and was instrumental in hammering out the c  0x standard on the topic   http   www hpl hp com techreports 2004 HPL-2004-209 html  That said there are several cross-platform thread C   libraries that work just fine in practice  Intel thread building blocks contains a tbb  thread object that closely approximates the c  0x standard and Boost has a boost  thread library that does the same   http   www threadingbuildingblocks org   http   www boost org doc libs 1 37 0 doc html thread html  Using boost  thread you d get something like    include  lt boost thread hpp gt   void task1             do stuff    void task2             do stuff    int main  int argc  char    argv        using namespace boost       thread thread 1   thread task1       thread thread 2   thread task2           do other stuff     thread 2 join        thread 1 join        return 0

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It largely depends on the library you decide to use  For instance  if you use the wxWidgets library  the creation of a thread would look like this   class RThread   public wxThread    public      RThread             wxThread wxTHREAD JOINABLE         private      RThread const RThread  amp copy    public      void  Entry void             Do             return 0             wxThread  CreateThread           Create thread     wxThread   hThread   new RThread           Start thread      hThread- gt Create         hThread- gt Run         return  hThread      If your main thread calls the CreateThread method  you ll create a new thread that will start executing the code in your  Entry  method  You ll have to keep a reference to the thread in most cases to join or stop it  More info here  wxThread documentation

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Create a function that you want the thread to execute  eg   void task1 std  string msg        std  cout  lt  lt   task1 says     lt  lt  msg      Now create the thread object that will ultimately invoke the function above like so   std  thread t1 task1   Hello       You need to  include  lt thread gt  to access the std  thread class   The constructor s arguments are the function the thread will execute  followed by the function s parameters  The thread is automatically started upon construction   If later on you want to wait for the thread to be done executing the function  call   t1 join        Joining means that the thread who invoked the new thread will wait for the new thread to finish execution  before it will continue its own execution      The Code   include  lt string gt   include  lt iostream gt   include  lt thread gt   using namespace std      The function we want to execute on the new thread  void task1 string msg        cout  lt  lt   task1 says     lt  lt  msg     int main            Constructs the new thread and runs it  Does not block execution      thread t1 task1   Hello            Do other things            Makes the main thread wait for the new thread to finish execution  therefore blocks its own execution      t1 join        More information about std  thread here   On GCC  compile with -std c  0x -pthread  This should work for any operating-system  granted your compiler supports this  C  11  feature

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include  lt thread gt   include  lt iostream gt   include  lt vector gt  using namespace std   void doSomething int id        cout  lt  lt  id  lt  lt    n             Spawns n threads     void spawnThreads int n        std  vector lt thread gt  threads n          spawn n threads      for  int i   0  i  lt  n  i              threads i    thread doSomething  i   1              for  auto amp  th   threads            th join             int main         spawnThreads 10

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include  lt thread gt   include  lt iostream gt   include  lt vector gt  using namespace std   void doSomething int id        cout  lt  lt  id  lt  lt    n             Spawns n threads     void spawnThreads int n        std  vector lt thread gt  threads n          spawn n threads      for  int i   0  i  lt  n  i              threads i    thread doSomething  i   1              for  auto amp  th   threads            th join             int main         spawnThreads 10

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When searching for an example of a C   class that calls one of its own instance methods in a new thread  this question comes up  but we were not able to use any of these answers that way  Here s an example that does that   Class h  class DataManager   public      bool hasData      void getData        bool dataAvailable         Class cpp   include  DataManager h   void DataManager  getData            perform background data munging     hasData   true         be sure to notify on the main thread    bool DataManager  dataAvailable         if  hasData                return true            else               std  thread t  amp DataManager  getData  this           t detach       as opposed to  join  which runs on the current thread           Note that this example doesn t get into mutex or locking

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There is also a POSIX library for POSIX operating systems   Check for compatability    include  lt stdio h gt   include  lt stdlib h gt   include  lt pthread h gt   include  lt iostream gt   void  task void  argument         char  msg        msg    char  argument        std  cout lt  lt msg lt  lt std  endl     int main        pthread t thread1  thread2      int i1 i2      i1   pthread create   amp thread1  NULL  task   void    thread 1        i2   pthread create   amp thread2  NULL  task   void    thread 2         pthread join thread1 NULL       pthread join thread2 NULL       return 0       compile with -lpthread      http   en wikipedia org wiki POSIX Threads

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Well  technically any such object will wind up being built over a C-style thread library because C   only just specified a stock std  thread model in c  0x  which was just nailed down and hasn t yet been implemented  The problem is somewhat systemic  technically the existing c   memory model isn t strict enough to allow for well defined semantics for all of the  happens before  cases  Hans Boehm wrote an paper on the topic a while back and was instrumental in hammering out the c  0x standard on the topic   http   www hpl hp com techreports 2004 HPL-2004-209 html  That said there are several cross-platform thread C   libraries that work just fine in practice  Intel thread building blocks contains a tbb  thread object that closely approximates the c  0x standard and Boost has a boost  thread library that does the same   http   www threadingbuildingblocks org   http   www boost org doc libs 1 37 0 doc html thread html  Using boost  thread you d get something like    include  lt boost thread hpp gt   void task1             do stuff    void task2             do stuff    int main  int argc  char    argv        using namespace boost       thread thread 1   thread task1       thread thread 2   thread task2           do other stuff     thread 2 join        thread 1 join        return 0

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There is also a POSIX library for POSIX operating systems   Check for compatability    include  lt stdio h gt   include  lt stdlib h gt   include  lt pthread h gt   include  lt iostream gt   void  task void  argument         char  msg        msg    char  argument        std  cout lt  lt msg lt  lt std  endl     int main        pthread t thread1  thread2      int i1 i2      i1   pthread create   amp thread1  NULL  task   void    thread 1        i2   pthread create   amp thread2  NULL  task   void    thread 2         pthread join thread1 NULL       pthread join thread2 NULL       return 0       compile with -lpthread      http   en wikipedia org wiki POSIX Threads

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It largely depends on the library you decide to use  For instance  if you use the wxWidgets library  the creation of a thread would look like this   class RThread   public wxThread    public      RThread             wxThread wxTHREAD JOINABLE         private      RThread const RThread  amp copy    public      void  Entry void             Do             return 0             wxThread  CreateThread           Create thread     wxThread   hThread   new RThread           Start thread      hThread- gt Create         hThread- gt Run         return  hThread      If your main thread calls the CreateThread method  you ll create a new thread that will start executing the code in your  Entry  method  You ll have to keep a reference to the thread in most cases to join or stop it  More info here  wxThread documentation

User · Answer

It largely depends on the library you decide to use  For instance  if you use the wxWidgets library  the creation of a thread would look like this   class RThread   public wxThread    public      RThread             wxThread wxTHREAD JOINABLE         private      RThread const RThread  amp copy    public      void  Entry void             Do             return 0             wxThread  CreateThread           Create thread     wxThread   hThread   new RThread           Start thread      hThread- gt Create         hThread- gt Run         return  hThread      If your main thread calls the CreateThread method  you ll create a new thread that will start executing the code in your  Entry  method  You ll have to keep a reference to the thread in most cases to join or stop it  More info here  wxThread documentation

User · Answer

Unless one want a separate function in global namespacs  we can use lambda functions for creating threads  One of the major advantage of creating thread using lambda is that we don t need to pass local parameters as an argument list  We can use capture list for the same and the closure property of lambda will take care of the lifecycle  Here is a sample code int main         int localVariable   100       thread th                  cout lt  lt  quot The Value of local variable   gt   quot  lt  lt localVariable lt  lt endl               th join         return 0     By far  I ve found C   lambdas to be the best way of creating threads especially for simpler thread functions

User · Answer

It largely depends on the library you decide to use  For instance  if you use the wxWidgets library  the creation of a thread would look like this   class RThread   public wxThread    public      RThread             wxThread wxTHREAD JOINABLE         private      RThread const RThread  amp copy    public      void  Entry void             Do             return 0             wxThread  CreateThread           Create thread     wxThread   hThread   new RThread           Start thread      hThread- gt Create         hThread- gt Run         return  hThread      If your main thread calls the CreateThread method  you ll create a new thread that will start executing the code in your  Entry  method  You ll have to keep a reference to the thread in most cases to join or stop it  More info here  wxThread documentation

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