Mercurial > noffle

diff src/lock.c @ 165:8ea6b5ddc5a5 noffle

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[svn] * src/lock.h,src/lock.c,src/noffle.c: Add lazy lock release. Only release the lock and close the databases if (a) another process signals us SIGUSR1 indicating it wants the lock, or (b) it is explicitly requested by a call to new function Lock_syncDatabases(). When waiting for the lock, SIGUSR1 the holding process every second. This is all an attempt to minimise the number of times we need to close and open the database. When (ha!) the database is replaced by something that can handle multiple simultaneous writers (with appropriate locking) this won't be necessary.
author bears
date Thu, 25 Jan 2001 13:38:31 +0000
parents 3c71e28c8eef
children 7ba337dafb2c
line wrap: on
line diff
--- a/src/lock.c	Thu Jan 25 11:00:03 2001 +0000
+++ b/src/lock.c	Thu Jan 25 13:38:31 2001 +0000
@@ -1,7 +1,7 @@
 /*
   lock.c
 
-  $Id: lock.c 183 2000-07-25 12:14:54Z bears $
+  $Id: lock.c 249 2001-01-25 13:38:31Z bears $
 */
 
 #if HAVE_CONFIG_H
@@ -15,6 +15,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
+#include <signal.h>
 
 #if TIME_WITH_SYS_TIME
 #include <sys/time.h>
@@ -34,16 +35,47 @@
 #include "group.h"
 #include "request.h"
 #include "portable.h"
+#include "util.h"
 
 struct Lock
 {
     const char *name;
     int lockFd;
     Str lockFile;
+    Bool doLazyLocking;
+    volatile Bool lazyClose;
+    volatile Bool lazyLockBusy;
 };
 
-struct Lock globalLock = { "global", -1, "" };
-struct Lock fetchLock = { "fetch", -1, "" };
+static struct Lock globalLock = { "global", -1, "", TRUE };
+static struct Lock fetchLock = { "fetch", -1, "", FALSE };
+
+static sig_t oldHandler = NULL;
+
+/* Block/unblock SIGUSR1. */
+static Bool
+blockSignal( Bool block )
+{
+    sigset_t sigs;
+
+    sigemptyset(&sigs);
+    sigaddset(&sigs, SIGUSR1);
+    
+    for(;;)
+    {
+	if ( sigprocmask( block ? SIG_BLOCK : SIG_UNBLOCK, &sigs, NULL ) != 0 )
+	{
+	    if ( errno != EINTR )
+	    {
+		Log_err( "Can't block/unblock signal" );
+		return FALSE;
+	    }
+	}
+	else
+	    return TRUE;
+    }
+    /* NOTREACHED */
+}
 
 /* Check the global lock held. */
 static Bool
@@ -52,6 +84,14 @@
     return ( lock->lockFd != -1 );    
 }
 
+static void
+lockWaitAlarm( int sig )
+{
+    UNUSED( sig );
+    
+    return;
+}
+
 static Bool
 waitLock( struct Lock *lock, enum LockRequestWait wait )
 {
@@ -74,12 +114,37 @@
     l.l_len = 0;
     if ( wait == LOCK_WAIT )
     {
-	if ( fcntl( fd, F_SETLKW, &l ) < 0 )
+	sig_t oldAlarmHandler;
+	unsigned oldAlarm;
+
+	oldAlarmHandler = Utl_installSignalHandler( SIGALRM, lockWaitAlarm );
+	oldAlarm = alarm( 1 );
+	for(;;)
 	{
-	    Log_err( "Cannot lock %s: %s", lock->lockFile, strerror( errno ) );
-	    close( lock->lockFd );
-	    return FALSE;
+	    alarm( 1 );
+	    if ( fcntl( fd, F_SETLKW, &l ) < 0 )
+		if ( errno != EINTR )
+		{
+		    Utl_installSignalHandler( SIGALRM, oldAlarmHandler );
+		    alarm( oldAlarm );
+		    Log_err( "Cannot lock %s: %s", lock->lockFile,
+			     strerror( errno ) );
+		    close( lock->lockFd );
+		    return FALSE;
+		}
+		else
+		{
+		    /* Send SIGUSR1 to the process holding the lock. */
+		    if ( fcntl( fd, F_GETLK, &l) == 0 && l.l_type != F_UNLCK )
+			if ( kill( l.l_pid, SIGUSR1 ) < 0 )
+			    Log_err( "Can't signal process %d: %s", l.l_pid,
+				     strerror( errno ) );
+		}
+	    else
+		break;
 	}
+	Utl_installSignalHandler( SIGALRM, oldAlarmHandler );
+	alarm( oldAlarm );
     }
     else
     {
@@ -113,11 +178,10 @@
     Log_dbg( "Releasing lock" );
 }
 
-
-/* Open all databases and set global lock. */
-Bool
-Lock_openDatabases( void )
+static Bool
+openDatabases( void )
 {
+    globalLock.lazyClose = FALSE;
     if ( ! waitLock( &globalLock, LOCK_WAIT ) )
     {
 	Log_err( "Could not get write lock" );
@@ -145,25 +209,98 @@
 	return FALSE;
     }
 
+    globalLock.lazyClose = globalLock.doLazyLocking;
+    globalLock.lazyLockBusy = TRUE;
     return TRUE;
 }
 
+static void
+closeDatabases( void )
+{
+    Grp_close();
+    Db_close();
+    Req_close();
+    releaseLock( &globalLock );
+    globalLock.lazyLockBusy = FALSE;
+    globalLock.lazyClose = FALSE;
+}
+
+static void
+lockSignal( int sig )
+{
+    UNUSED( sig );
+
+    if ( globalLock.lazyLockBusy )
+	globalLock.lazyClose = FALSE;
+    else
+	closeDatabases();
+    return;
+}
+
+/* Open all databases and set global lock. */
+Bool
+Lock_openDatabases( void )
+{
+    Bool res;
+
+    /* First time - need to initialise signal handler? */
+    if ( oldHandler == NULL )
+	oldHandler = Utl_installSignalHandler( SIGUSR1, lockSignal );
+
+    if ( ! blockSignal( TRUE ) )
+	return FALSE;
+    
+    if ( ! globalLock.lazyClose )
+	res = openDatabases();
+    else
+	res = TRUE;
+    
+    globalLock.lazyLockBusy = res;
+
+    if ( ! blockSignal( FALSE ) )
+	return FALSE;
+
+    return res;
+}
 
 /* Close all databases and release global lock. */
 void
 Lock_closeDatabases( void )
 {
-    Grp_close();
-    Db_close();
-    Req_close();
-    releaseLock( &globalLock );
+    blockSignal( TRUE );
+    
+    if ( ! globalLock.lazyClose )
+	closeDatabases();
+    else
+	globalLock.lazyLockBusy = FALSE;
+    
+    blockSignal( FALSE );
+}
+
+/* Sync al databases to disc. Maintain global lock status. */
+void
+Lock_syncDatabases( void )
+{
+    Bool wasOpen;
+    
+    if ( gotLock( &globalLock ) )
+    {
+	blockSignal( TRUE );
+    
+	wasOpen = globalLock.lazyLockBusy;
+	closeDatabases();
+	if ( wasOpen )
+	    openDatabases();
+	
+	blockSignal( FALSE );
+    }
 }
 
 /* Check the global lock held. */
 Bool
 Lock_gotLock( void )
 {
-    return gotLock( &globalLock );
+    return globalLock.lazyLockBusy;
 }
 
 /* Get fetch lock. */