## NAME

ACE_SV_Semaphore_Complex - This is a more complex semaphore wrapper that handles race conditions for initialization correctly...

## SYNOPSIS

    #include <ace/ACE_SV_Semaphore_Complex.h>

    class ACE_SV_Semaphore_Complex : private ACE_SV_Semaphore_Simple
    {
      public:
        enum{ ACE_CREATE = IPC_CREAT, ACE_OPEN = 0 };
        ACE_SV_Semaphore_Complex (void);
        ACE_SV_Semaphore_Complex (
            key_t key,
            int create = ACE_SV_Semaphore_Complex::ACE_CREATE,
            int initial_value = 1,
            u_short nsems = 1,
            int perms = ACE_DEFAULT_FILE_PERMS
            );
        ACE_SV_Semaphore_Complex (
            const char *name,
            int create = ACE_SV_Semaphore_Complex::ACE_CREATE,
            int initial_value = 1,
            u_short nsems = 1,
            int perms = ACE_DEFAULT_FILE_PERMS
            );
        ~ACE_SV_Semaphore_Complex (void);
        int open (
            const char *name,
            int flags = ACE_SV_Semaphore_Simple::ACE_CREATE,
            int initial_value = 1,
            u_short nsems = 1,
            int perms = ACE_DEFAULT_FILE_PERMS
            );
        int open (
            key_t key,
            int flags = ACE_SV_Semaphore_Simple::ACE_CREATE,
            int initial_value = 1,
            u_short nsems = 1,
            int perms = ACE_DEFAULT_FILE_PERMS
            );
        int close (void);
        int acquire (u_short n = 0, int flags = 0) const;
        int acquire_read (u_short n = 0, int flags = 0) const;
        int acquire_write (u_short n = 0, int flags = 0) const;
        int tryacquire (u_short n = 0, int flags = 0) const;
        int tryacquire_read (u_short n = 0, int flags = 0) const;
        int tryacquire_write (u_short n = 0, int flags = 0) const;
        int release (u_short n = 0, int flags = 0) const;
        int op (int val, u_short n = 0, int flags = 0) const;
        int op (sembuf op_vec[], u_short n) const;
        int control (int cmd, semun arg, u_short n = 0) const;
        int control (int cmd, int value = 0, u_short n = 0) const;
        ACE_USING ACE_SV_Semaphore_Simple::get_id;
        ACE_USING ACE_SV_Semaphore_Simple::remove;
        void dump (void) const;
        ACE_ALLOC_HOOK_DECLARE;
      private:
        static const int BIGCOUNT_;
        static sembuf op_lock_[2];
        static sembuf op_endcreate_[2];
        static sembuf op_open_[1];
        static sembuf op_close_[3];
        static sembuf op_unlock_[1];
    };

## DESCRIPTION

This code is a port to C++, inspired by: W. Richard Stevens from his book: UNIX Network Programming (Prentice Hall, ISBN 0-13-949876-1 - 1990) ACE_SV_Semaphore Interface: we provide a simpler and easier to understand interface to the System V ACE_SV_Semaphore calls. We create and use a 2 + n-member set for the requested ACE_SV_Semaphore. The first member, [0], is a counter used to know when all processes have finished with the ACE_SV_Semaphore. The counter is initialized to a large number, decremented on every create or open and incremented on every close. This way we can use the "adjust" feature provided by System V so that any process that exit's without calling close() is accounted for. It doesn't help us if the last process does this (as we have no way of getting control to remove the ACE_SV_Semaphore) but it will work if any process other than the last does an exit (intentional or unintentional).

The second member, [1], of the ACE_SV_Semaphore is used as a lock variable to avoid any race conditions in the create() and close() functions.

The members beyond [1] are actual ACE_SV_Semaphore values in the array of SV_Semaphores (which may be sized by the user in the constructor).

## Initialization and termination methods.

    ACE_SV_Semaphore_Complex (void);

    ACE_SV_Semaphore_Complex (
        key_t key,
        int create = ACE_SV_Semaphore_Complex::ACE_CREATE,
        int initial_value = 1,
        u_short nsems = 1,
        int perms = ACE_DEFAULT_FILE_PERMS
        );

    ACE_SV_Semaphore_Complex (
        const char *name,
        int create = ACE_SV_Semaphore_Complex::ACE_CREATE,
        int initial_value = 1,
        u_short nsems = 1,
        int perms = ACE_DEFAULT_FILE_PERMS
        );

    ~ACE_SV_Semaphore_Complex (void);

    int open (
        const char *name,
        int flags = ACE_SV_Semaphore_Simple::ACE_CREATE,
        int initial_value = 1,
        u_short nsems = 1,
        int perms = ACE_DEFAULT_FILE_PERMS
        );

Open or create an array of SV_Semaphores. We return 0 if all is OK, else -1.

    int open (
        key_t key,
        int flags = ACE_SV_Semaphore_Simple::ACE_CREATE,
        int initial_value = 1,
        u_short nsems = 1,
        int perms = ACE_DEFAULT_FILE_PERMS
        );

Open or create an array of SV_Semaphores. We return 0 if all is OK, else -1.

    int close (void);

Close an ACE_SV_Semaphore. Unlike the `remove` method, this method is for a process to call before it exits, when it is done with the ACE_SV_Semaphore. We "decrement" the counter of processes using the ACE_SV_Semaphore, and if this was the last one, we can remove the ACE_SV_Semaphore.

## Semaphore acquire and release methods.

    int acquire (u_short n = 0, int flags = 0) const;

Acquire the semaphore.

    int acquire_read (u_short n = 0, int flags = 0) const;

Acquire a semaphore for reading.

    int acquire_write (u_short n = 0, int flags = 0) const;

Acquire a semaphore for writing

    int tryacquire (u_short n = 0, int flags = 0) const;

Try to acquire the semaphore.

    int tryacquire_read (u_short n = 0, int flags = 0) const;

Try to acquire the semaphore for reading.

    int tryacquire_write (u_short n = 0, int flags = 0) const;

Try to acquire the semaphore for writing.

    int release (u_short n = 0, int flags = 0) const;

Release the semaphore.

## Semaphore operation methods.

    int op (int val, u_short n = 0, int flags = 0) const;

    int op (sembuf op_vec[], u_short n) const;

## Semaphore control methods.

    int control (int cmd, semun arg, u_short n = 0) const;

    int control (int cmd, int value = 0, u_short n = 0) const;

## Upgrade access control...

    ACE_USING ACE_SV_Semaphore_Simple::get_id;

    ACE_USING ACE_SV_Semaphore_Simple::remove;

    void dump (void) const;

Dump the state of an object.

    ACE_ALLOC_HOOK_DECLARE;

Declare the dynamic allocation hooks.

## AUTHOR

Doug Schmidt

## LIBRARY

ace