libassa
3.5.0
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#include <Semaphore.h>
Public Member Functions | |
Semaphore () | |
Constructor. | |
virtual | ~Semaphore () |
Destructor. | |
int | create (key_t key_, int initval_=1) |
Create a semaphore with a specified initial value. | |
int | open (key_t key_) |
Open a semaphore that must already exist. | |
void | close () |
Close a semaphore. | |
void | remove () |
Remove a semaphore. | |
void | wait () |
Wait until a semaphore's value is greater then 0, then decrement it by 1 and return. | |
void | signal () |
Increment a semaphore by 1. | |
void | op (int val_) |
General semaphore operation. | |
key_t | key () const |
Get key. | |
int | id () const |
Get id. | |
void | dump (void) const |
Dump the objects state along with the state of the semaphore (if connected) to the log file. | |
Protected Member Functions | |
void | init () |
Initalize by invalidating data members. | |
Protected Attributes | |
key_t | m_key |
Semaphore's key. | |
int | m_id |
Semaphore's id. | |
Static Protected Attributes | |
static const int | BIGCOUNT = 10000 |
static sembuf | m_op_lock [2] |
Wait for lock to equal 0, then increment lock to 1 - this locks it. | |
static sembuf | m_op_endcreate [2] |
Decrement process counter with undo on exit, then decrement lock back to 0. | |
static sembuf | m_op_open [2] |
Decrement process counter with undo on exit. | |
static sembuf | m_op_close [3] |
Wait for lock to equal 0, then increment lock to 1 (lock it), then increment process counter. | |
static sembuf | m_op_unlock [1] |
Decremetn lock back to 0. | |
static sembuf | m_op_op [1] |
Decrement or increment semaphore with undo on exit. |
Definition at line 66 of file Semaphore.h.
ASSA::Semaphore::Semaphore | ( | ) | [inline] |
Constructor.
Definition at line 190 of file Semaphore.h.
References init(), ASSA::SEM, and trace_with_mask.
{ trace_with_mask("Semaphore::Semaphore", SEM); init (); }
ASSA::Semaphore::~Semaphore | ( | ) | [inline, virtual] |
Destructor.
Definition at line 199 of file Semaphore.h.
References close(), m_id, ASSA::SEM, and trace_with_mask.
{ trace_with_mask("Semaphore::~Semaphore", SEM); if (m_id > 0) { this->close (); } }
void Semaphore::close | ( | void | ) |
Close a semaphore.
Unlike the Semaphore::remove () function, this function is for a process to call before it exits, when it is done with the semaphore. We decrement the counter of processes using the semaphore, and if this was the last one, Semaphore::remove () is called to remove the semaphore. Calling this method also invalidates object for subsequent operations.
Definition at line 221 of file Semaphore.cpp.
References ASSA::ASSAERR, Assure_exit, BIGCOUNT, EL, init(), m_id, m_op_close, m_op_unlock, ASSA::SEM, and trace_with_mask.
Referenced by ~Semaphore().
{ trace_with_mask("Semaphore::close", SEM); register int semval; if (m_id < 0) return; /* First get the lock on semaphore, then increment process counter. */ if (semop (m_id, &m_op_close[0], 3) < 0) { EL((ASSAERR,"Can't semop(2)\n")); Assure_exit(false); } /* Now that we have a lock, read the value of the process counter to see if this is the last reference to the semaphore. There is a race condition here (same as in Semaphore::create()). */ if ((semval = semctl (m_id, 1, GETVAL, 0)) < 0) { EL((ASSAERR,"Can't GETVAL\n")); Assure_exit(false); } if (semval > BIGCOUNT) { EL((ASSAERR,"sem[1] > BIGCOUNT\n")); Assure_exit(false); } else if (semval == BIGCOUNT) { remove (); } else if (semop (m_id, &m_op_unlock[0], 1) < 0) { EL((ASSAERR,"Can't unlock\n")); Assure_exit(false); } /*--- Invalidate ---*/ init (); }
int Semaphore::create | ( | key_t | key_, |
int | initval_ = 1 |
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) |
Create a semaphore with a specified initial value.
If the semaphore already exists, we don't initialize it (of course).
key_ | Semaphore's key |
initval_ | Initiali value (default : 1) |
Definition at line 77 of file Semaphore.cpp.
References ASSA::ASSAERR, Assure_exit, BIGCOUNT, EL, m_id, m_key, m_op_endcreate, m_op_lock, ASSA::SEM, and trace_with_mask.
{ trace_with_mask("Semaphore::create", SEM); register int semval; union semnum { int val; struct semid_ds* buf; ushort* array; } semctrl_arg; if (IPC_PRIVATE == key_) { EL((ASSAERR,"Not intended for private semaphores\n")); return (-1); } else if (key_ == (key_t) -1) { EL((ASSAERR,"Probably an ftok() error by caller\n")); return (-1); } m_key = key_; bool done = false; while (!done) { if ( (m_id = semget (m_key, 3, 0666 | IPC_CREAT)) < 0) { EL((ASSAERR,"Permission problem or kernel tables full\n")); return (-1); } /* When the semaphore is created, we know that the value of all 3 set members is 0. Get a lock on the semaphore by waiting for [2] to equal 0, then increment it. There is a race condition here. There is a possibility that between the semget(2) and semop(2) below, another process can cal Semaphore:::close () member function which can remove a semaphore if that process is the last one using it. Therefore, we handle the error condition of an invalid semaphore ID specially below, and if it does happen, we just go back and create it again. */ if (semop (m_id, &m_op_lock[0], 2) < 0) { if (errno == EINVAL) { continue; } EL((ASSAERR,"Can't lock semaphore\n")); Assure_exit (false); } done = true; } // while (!done) /* Get the value of the process counter. If it equals 0, then no one has initialized the semaphore yet. */ if ((semval = semctl (m_id, 1, GETVAL, 0)) < 0) { EL((ASSAERR,"Can't GETVAL\n")); Assure_exit (false); } if (semval == 0) { /* We could initalize by doing a SETALL, but that would clear the adjust value that we set when we locked the semaphore above. Instead, we'll do two system calls to initialize semaphore value [0] and process counter [1]. */ semctrl_arg.val = initval_; if (semctl (m_id, 0, SETVAL, semctrl_arg) < 0) { EL((ASSAERR,"Can't SETVAL[0]\n")); Assure_exit (false); } semctrl_arg.val = BIGCOUNT; if (semctl (m_id, 1, SETVAL, semctrl_arg) < 0) { EL((ASSAERR,"Can't SETVAL[1]\n")); Assure_exit (false); } } // if (semval == 0) /*--- Decrement the process counter and then release the lock. ---*/ if (semop (m_id, &m_op_endcreate[0], 2) < 0) { EL((ASSAERR,"Error on semop (ndcreate)\n")); Assure_exit (false); } return (m_id); }
void Semaphore::dump | ( | void | ) | const |
Dump the objects state along with the state of the semaphore (if connected) to the log file.
Definition at line 294 of file Semaphore.cpp.
References DL, ASSA::ends(), m_id, m_key, ASSA::SEM, and trace_with_mask.
Referenced by op().
{ trace_with_mask("Semaphore::dump", SEM); std::ostringstream msg; msg << "\n\n\tKey.....: "; if (m_key == (key_t) -1) { msg << m_key; } else { msg << "0x" << std::hex << m_key << std::dec; } msg << "\n\tID......: " << m_id << "\n\n"; if (m_id >= 0 && m_key >= (key_t) -1) { msg << "\tsemval [0]\tproc counter[1]\tlock [2]\n" << "\t----------\t---------------\t--------\n"; /*--- Get value of element in semaphore set ---*/ msg << "\t " << semctl (m_id, 0, GETVAL) << "\t\t " << semctl (m_id, 1, GETVAL) << "\t\t " << semctl (m_id, 2, GETVAL); } else { msg << "Semaphore id = -1. No info is available."; } msg << std::ends; DL((SEM,"%s\n\n", msg.str ().c_str ())); }
int ASSA::Semaphore::id | ( | ) | const [inline] |
void ASSA::Semaphore::init | ( | ) | [inline, protected] |
Initalize by invalidating data members.
Definition at line 210 of file Semaphore.h.
Referenced by close(), remove(), and Semaphore().
key_t ASSA::Semaphore::key | ( | ) | const [inline] |
void Semaphore::op | ( | int | val_ | ) |
General semaphore operation.
Increment or decrement by a user-specified amount (positive or negative; amount can't be zero!).
Definition at line 264 of file Semaphore.cpp.
References ASSA::ASSAERR, Assure_exit, dump(), EL, m_id, m_op_op, ASSA::SEM, and trace_with_mask.
Referenced by signal(), and wait().
{ /* Test if m_id is still valid. If it fails, then * next operation is failing because of it. If not, * then something else happens here. */ trace_with_mask("Semaphore::op", SEM); int semval = 0; dump (); if ((semval = semctl (m_id, 1, GETVAL, 0)) < 0) { EL((ASSAERR,"Can't GETVAL\n")); Assure_exit (false); } /* This will fail on Solaris? */ if ((m_op_op[0].sem_op = value_) == 0) { EL((ASSAERR,"Can't have value_ == 0\n")); Assure_exit(false); } if (semop (m_id, &m_op_op[0], 1) < 0) { EL((ASSAERR,"sem_op error\n")); Assure_exit(false); } }
int Semaphore::open | ( | key_t | key_ | ) |
Open a semaphore that must already exist.
This function should be used, instead of Semaphore::create (), if the caller knows that the semaphore must already exist. For example, a client from a client-server pair would use this, if its server's responsibility to create the semaphore.
key_ | Semaphore's key |
Definition at line 176 of file Semaphore.cpp.
References ASSA::ASSAERR, Assure_exit, EL, m_id, m_key, m_op_open, ASSA::SEM, and trace_with_mask.
{ trace_with_mask("Semaphore::open", SEM); if (IPC_PRIVATE == key_) { EL((ASSAERR,"Not intended for private semaphores\n")); return (-1); } else if (key_ == (key_t) -1) { EL((ASSAERR,"Probably an ftok() error by caller\n")); return (-1); } m_key = key_; if ((m_id = semget (m_key, 3, 0)) < 0) { EL((ASSAERR,"Error on semget(3)")); return (-1); } /*--- Decrement the process counter. No need for lock ---*/ if (semop (m_id, &m_op_open[0], 1) < 0) { EL((ASSAERR,"Error on semget(open)\n")); Assure_exit(false); } return (m_id); }
void Semaphore::remove | ( | ) |
Remove a semaphore.
This call is intended to be called by a server, for example, when it is being shut down, as we do an IPC_RMID on the semaphore, regardless whether other processes may be using it or not. Most other processes should use Semaphore::close () instead. Calling this method also invalidates object for subsequent operations.
Definition at line 206 of file Semaphore.cpp.
References ASSA::ASSAERR, Assure_exit, EL, init(), m_id, m_key, ASSA::SEM, and trace_with_mask.
{ trace_with_mask("Semaphore::remove", SEM); if (m_id < 0 || m_key == ((key_t) -1) ) return; if (semctl (m_id, 0, IPC_RMID, 0) < 0) { EL((ASSAERR,"Can't IPC_RMID\n")); Assure_exit(false); } init (); }
void ASSA::Semaphore::signal | ( | ) | [inline] |
Increment a semaphore by 1.
Tanenbaum's UP operation.
Definition at line 226 of file Semaphore.h.
References op(), ASSA::SEM, and trace_with_mask.
{ trace_with_mask("Semaphore::signal", SEM); op (1); }
void ASSA::Semaphore::wait | ( | ) | [inline] |
Wait until a semaphore's value is greater then 0, then decrement it by 1 and return.
Tanenbaum's DOWN operation.
Definition at line 218 of file Semaphore.h.
References op(), ASSA::SEM, and trace_with_mask.
{ trace_with_mask("Semaphore::wait", SEM); op (-1); }
const int ASSA::Semaphore::BIGCOUNT = 10000 [static, protected] |
Definition at line 156 of file Semaphore.h.
int ASSA::Semaphore::m_id [protected] |
key_t ASSA::Semaphore::m_key [protected] |
sembuf Semaphore::m_op_close [static, protected] |
{ {2, 0, 0}, {2, 1, SEM_UNDO}, {1, 1, SEM_UNDO} }
Wait for lock to equal 0, then increment lock to 1 (lock it), then increment process counter.
Definition at line 175 of file Semaphore.h.
Referenced by close().
sembuf Semaphore::m_op_endcreate [static, protected] |
{ {1, -1, SEM_UNDO}, {2, -1, SEM_UNDO} }
Decrement process counter with undo on exit, then decrement lock back to 0.
Definition at line 165 of file Semaphore.h.
Referenced by create().
sembuf Semaphore::m_op_lock [static, protected] |
{ {2, 0, 0}, {2, 1, SEM_UNDO} }
Wait for lock to equal 0, then increment lock to 1 - this locks it.
Definition at line 160 of file Semaphore.h.
Referenced by create().
sembuf Semaphore::m_op_op [static, protected] |
{ {0, 99, SEM_UNDO} }
Decrement or increment semaphore with undo on exit.
The 99 is set to the actual amount to add or substract (positive or negative).
Definition at line 185 of file Semaphore.h.
Referenced by op().
sembuf Semaphore::m_op_open [static, protected] |
{ {1, -1, SEM_UNDO}, }
Decrement process counter with undo on exit.
Definition at line 170 of file Semaphore.h.
Referenced by open().
sembuf Semaphore::m_op_unlock [static, protected] |
{ {2, -1, SEM_UNDO} }
Decremetn lock back to 0.
Definition at line 179 of file Semaphore.h.
Referenced by close().