win32_sema.c File Reference

#include "postgres.h"
#include "miscadmin.h"
#include "storage/ipc.h"
#include "storage/pg_sema.h"

Include dependency graph for win32_sema.c:

Go to the source code of this file.

Functions
static void	ReleaseSemaphores (int code, Datum arg)
Size	PGSemaphoreShmemSize (int maxSemas)
void	PGReserveSemaphores (int maxSemas)
PGSemaphore	PGSemaphoreCreate (void)
void	PGSemaphoreReset (PGSemaphore sema)
void	PGSemaphoreLock (PGSemaphore sema)
void	PGSemaphoreUnlock (PGSemaphore sema)
bool	PGSemaphoreTryLock (PGSemaphore sema)

Variables
static HANDLE *	mySemSet
static int	numSems
static int	maxSems

Function Documentation

PGReserveSemaphores()

void PGReserveSemaphores

(

int

maxSemas

)

Definition at line 47 of file win32_sema.c.

{
    mySemSet = (HANDLE *) malloc(maxSemas * sizeof(HANDLE));
    if (mySemSet == NULL)
        elog(PANIC, "out of memory");
    numSems = 0;
    maxSems = maxSemas;
 
    on_shmem_exit(ReleaseSemaphores, 0);
}

References elog, malloc, maxSems, mySemSet, numSems, on_shmem_exit(), PANIC, and ReleaseSemaphores().

PGSemaphoreCreate()

PGSemaphore PGSemaphoreCreate

(

void

)

Definition at line 79 of file win32_sema.c.

{
    HANDLE      cur_handle;
    SECURITY_ATTRIBUTES sec_attrs;
 
    /* Can't do this in a backend, because static state is postmaster's */
    Assert(!IsUnderPostmaster);
 
    if (numSems >= maxSems)
        elog(PANIC, "too many semaphores created");
 
    ZeroMemory(&sec_attrs, sizeof(sec_attrs));
    sec_attrs.nLength = sizeof(sec_attrs);
    sec_attrs.lpSecurityDescriptor = NULL;
    sec_attrs.bInheritHandle = TRUE;
 
    /* We don't need a named semaphore */
    cur_handle = CreateSemaphore(&sec_attrs, 1, 32767, NULL);
    if (cur_handle)
    {
        /* Successfully done */
        mySemSet[numSems++] = cur_handle;
    }
    else
        ereport(PANIC,
                (errmsg("could not create semaphore: error code %lu",
                        GetLastError())));
 
    return (PGSemaphore) cur_handle;
}

References Assert(), elog, ereport, errmsg(), IsUnderPostmaster, maxSems, mySemSet, numSems, and PANIC.

PGSemaphoreLock()

void PGSemaphoreLock

(

PGSemaphore

sema

)

Definition at line 132 of file win32_sema.c.

{
    HANDLE      wh[2];
    bool        done = false;
 
    /*
     * Note: pgwin32_signal_event should be first to ensure that it will be
     * reported when multiple events are set.  We want to guarantee that
     * pending signals are serviced.
     */
    wh[0] = pgwin32_signal_event;
    wh[1] = sema;
 
    /*
     * As in other implementations of PGSemaphoreLock, we need to check for
     * cancel/die interrupts each time through the loop.  But here, there is
     * no hidden magic about whether the syscall will internally service a
     * signal --- we do that ourselves.
     */
    while (!done)
    {
        DWORD       rc;
 
        CHECK_FOR_INTERRUPTS();
 
        rc = WaitForMultipleObjectsEx(2, wh, FALSE, INFINITE, TRUE);
        switch (rc)
        {
            case WAIT_OBJECT_0:
                /* Signal event is set - we have a signal to deliver */
                pgwin32_dispatch_queued_signals();
                break;
            case WAIT_OBJECT_0 + 1:
                /* We got it! */
                done = true;
                break;
            case WAIT_IO_COMPLETION:
 
                /*
                 * The system interrupted the wait to execute an I/O
                 * completion routine or asynchronous procedure call in this
                 * thread.  PostgreSQL does not provoke either of these, but
                 * atypical loaded DLLs or even other processes might do so.
                 * Now, resume waiting.
                 */
                break;
            case WAIT_FAILED:
                ereport(FATAL,
                        (errmsg("could not lock semaphore: error code %lu",
                                GetLastError())));
                break;
            default:
                elog(FATAL, "unexpected return code from WaitForMultipleObjectsEx(): %lu", rc);
                break;
        }
    }
}

References CHECK_FOR_INTERRUPTS, elog, ereport, errmsg(), FATAL, pgwin32_dispatch_queued_signals(), and pgwin32_signal_event.

PGSemaphoreReset()

void PGSemaphoreReset

(

PGSemaphore

sema

)

Definition at line 116 of file win32_sema.c.

{
    /*
     * There's no direct API for this in Win32, so we have to ratchet the
     * semaphore down to 0 with repeated trylock's.
     */
    while (PGSemaphoreTryLock(sema))
         /* loop */ ;
}

References PGSemaphoreTryLock().

PGSemaphoreShmemSize()

Size PGSemaphoreShmemSize

(

int

maxSemas

)

Definition at line 31 of file win32_sema.c.

{
    /* No shared memory needed on Windows */
    return 0;
}

PGSemaphoreTryLock()

bool PGSemaphoreTryLock

(

PGSemaphore

sema

)

Definition at line 210 of file win32_sema.c.

{
    DWORD       ret;
 
    ret = WaitForSingleObject(sema, 0);
 
    if (ret == WAIT_OBJECT_0)
    {
        /* We got it! */
        return true;
    }
    else if (ret == WAIT_TIMEOUT)
    {
        /* Can't get it */
        errno = EAGAIN;
        return false;
    }
 
    /* Otherwise we are in trouble */
    ereport(FATAL,
            (errmsg("could not try-lock semaphore: error code %lu",
                    GetLastError())));
 
    /* keep compiler quiet */
    return false;
}

References EAGAIN, ereport, errmsg(), and FATAL.

Referenced by PGSemaphoreReset().

PGSemaphoreUnlock()

void PGSemaphoreUnlock

(

PGSemaphore

sema

)

Definition at line 196 of file win32_sema.c.

{
    if (!ReleaseSemaphore(sema, 1, NULL))
        ereport(FATAL,
                (errmsg("could not unlock semaphore: error code %lu",
                        GetLastError())));
}

References ereport, errmsg(), and FATAL.

ReleaseSemaphores()

static void ReleaseSemaphores ( int  code, Datum  arg  )

static

Definition at line 64 of file win32_sema.c.

{
    int         i;
 
    for (i = 0; i < numSems; i++)
        CloseHandle(mySemSet[i]);
    free(mySemSet);
}

References free, i, mySemSet, and numSems.

Referenced by PGReserveSemaphores().

Variable Documentation

maxSems

int maxSems

static

Definition at line 22 of file win32_sema.c.

Referenced by PGReserveSemaphores(), and PGSemaphoreCreate().

mySemSet

HANDLE* mySemSet

static

Definition at line 20 of file win32_sema.c.

Referenced by PGReserveSemaphores(), PGSemaphoreCreate(), and ReleaseSemaphores().

numSems

int numSems

static

Definition at line 21 of file win32_sema.c.

Referenced by PGReserveSemaphores(), PGSemaphoreCreate(), and ReleaseSemaphores().