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## Class named_semaphore

boost::interprocess::named_semaphore

## Synopsis

    // In header: <boost/interprocess/sync/named_semaphore.hpp>

    class named_semaphore {
    public:
      // construct/copy/destruct
      named_semaphore(create_only_t, const char *, unsigned int,
                      const permissions & = permissions());
      named_semaphore(open_or_create_t, const char *, unsigned int,
                      const permissions & = permissions());
      named_semaphore(open_only_t, const char *);
      ~named_semaphore();

      // public member functions
      void post();
      void wait();
      bool try_wait();
      bool timed_wait(const boost::posix_time::ptime &);

      // public static functions
      static bool remove(const char *);
    };

## Description

A semaphore with a global name, so it can be found from different processes. Allows several resource sharing patterns and efficient acknowledgment mechanisms.

### `named_semaphore` public construct/copy/destruct

1.     named_semaphore(create_only_t, const char * name, unsigned int initialCount,
                       const permissions & perm = permissions());

   Creates a global semaphore with a name, and an initial count. If the semaphore can't be created throws `interprocess_exception`

2.     named_semaphore(open_or_create_t, const char * name,
                       unsigned int initialCount,
                       const permissions & perm = permissions());

   Opens or creates a global semaphore with a name, and an initial count. If the semaphore is created, this call is equivalent to `named_semaphore`(`create_only_t`, ...) If the semaphore is already created, this call is equivalent to `named_semaphore`(`open_only_t`, ... ) and initialCount is ignored.

3.     named_semaphore(open_only_t, const char * name);

   Opens a global semaphore with a name if that semaphore is previously. created. If it is not previously created this function throws `interprocess_exception`.

4.     ~named_semaphore();

   Destroys *this and indicates that the calling process is finished using the resource. The destructor function will deallocate any system resources allocated by the system for use by this process for this resource. The resource can still be opened again calling the open constructor overload. To erase the resource from the system use remove().

### `named_semaphore` public member functions

1.     void post();

   Increments the semaphore count. If there are processes/threads blocked waiting for the semaphore, then one of these processes will return successfully from its wait function. If there is an error an `interprocess_exception` exception is thrown.

2.     void wait();

   Decrements the semaphore. If the semaphore value is not greater than zero, then the calling process/thread blocks until it can decrement the counter. If there is an error an `interprocess_exception` exception is thrown.

3.     bool try_wait();

   Decrements the semaphore if the semaphore's value is greater than zero and returns true. If the value is not greater than zero returns false. If there is an error an `interprocess_exception` exception is thrown.

4.     bool timed_wait(const boost::posix_time::ptime & abs_time);

   Decrements the semaphore if the semaphore's value is greater than zero and returns true. Otherwise, waits for the semaphore to the posted or the timeout expires. If the timeout expires, the function returns false. If the semaphore is posted the function returns true. If there is an error throws sem_exception

### `named_semaphore` public static functions

1.     static bool remove(const char * name);

   Erases a named semaphore from the system. Returns false on error. Never throws.