CSS 430: Operating Systems - Process Synchronization Thread Synchronization in ThreadOS: Implementing SysLib methods join(), exit(), rawread(), rawwrite(), sync() Joe McCarthy CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Monitors A high-level abstraction that provides a convenient and effective mechanism for process synchronization Only one process may be active within the monitor at a time CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Syntax of a Monitor CSS 430: Operating Systems - Process Synchronization

Schematic view of a Monitor CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Condition Variables Condition x, y; Operations on a condition variable: x.wait () – a process that invokes the operation is suspended x.signal () – resumes one of processes (if any) that invoked x.wait () CSS 430: Operating Systems - Process Synchronization

Monitor with Condition Variables CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Java Synchronization Java provides synchronization at the language-level Thread-safe Every Java Object has an associated lock This lock is acquired by invoking a synchronized method This lock is released when exiting the synchronized method. Threads wanting to acquire the object lock are placed in the entry set for the object lock CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Java Synchronization When a thread invokes wait(): 1. It releases the object lock 2. Its state is set to Blocked 3. It is placed in the wait set for the object When a thread invokes notify(): 1. A thread T from the wait set is selected 2. T is moved from the wait set to the entry set 3. The state of T is set to Runnable CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization http://download.oracle.com/javase/6/docs/api/java/lang/Object.html CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Java Synchronization /usr/apps/CSS430/examples/os-book/ch6/java-synchronization/boundedbuffer CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Java Synchronization notify() may not notify the correct thread! /usr/apps/CSS430/examples/os-book/ch6/java-synchronization/boundedbuffer CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Test2e class Test2e extends Thread { public void run() { String[] args1 = SysLib.stringToArgs( "TestThread2 a 5000 0" ); String[] args2 = SysLib.stringToArgs( "TestThread2 b 1000 0" ); String[] args3 = SysLib.stringToArgs( "TestThread2 c 3000 0" ); String[] args4 = SysLib.stringToArgs( "TestThread2 d 6000 0" ); String[] args5 = SysLib.stringToArgs( "TestThread2 e 500 0" ); SysLib.exec( args1 ); SysLib.exec( args2 ); SysLib.exec( args3 ); SysLib.exec( args4 ); SysLib.exec( args5 ); for (int i = 0; i < 5; i++ ) { int tid = SysLib.join(); SysLib.cout( "Thread tid=" + tid + " done\n” ); SysLib.cout( "Test2e finished; total time = " + totalTime + "\n" ); SysLib.exit(); } CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization TestThread2 class TestThread2 extends Thread { … public void run() { long totalExecutionTime = 0; long totalWaitTime = 0; activationTime = new Date().getTime(); for ( int burst = cpuBurst; burst > 0; burst -= TIMEQUANTUM ) { totalExecutionTime += TIMEQUANTUM; SysLib.sleep( TIMEQUANTUM ); } completionTime = new Date().getTime( ); long responseTime = activationTime - submissionTime; totalWaitTime = completionTime - submissionTime - executionTime; long turnaroundTime = completionTime - submissionTime; SysLib.cout( String.format( "%05d: Thread[%s]: response: %5d; wait: %5d; execution: %5d; turnaround: %5d\n", completionTime % 100000, name, responseTime, totalWaitTime, totalExecutionTime, turnaroundTime ) ); SysLib.exit(); CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Test2e output d-69-91-160-124:ThreadOS0 joe$ java Boot threadOS ver 1.0: Type ? for help threadOS: a new thread (thread=Thread[Thread-4,2,main] tid=0 pid=-1) -->l Shell l Shell threadOS: a new thread (thread=Thread[Thread-6,2,main] tid=1 pid=0) shell[1]% Test2e Test2e threadOS: a new thread (thread=Thread[Thread-9,2,main] tid=2 pid=1) threadOS: a new thread (thread=Thread[Thread-11,2,main] tid=3 pid=2) threadOS: a new thread (thread=Thread[Thread-13,2,main] tid=4 pid=2) threadOS: a new thread (thread=Thread[Thread-15,2,main] tid=5 pid=2) threadOS: a new thread (thread=Thread[Thread-17,2,main] tid=6 pid=2) threadOS: a new thread (thread=Thread[Thread-19,2,main] tid=7 pid=2) Thread[b]: response time = 3942 turnaround time = 4944 execution time = 1002 Thread tid=4 done Thread[e]: response time = 6944 turnaround time = 7445 execution time = 501 Thread tid=7 done Thread[a]: response time = 2941 turnaround time = 7948 execution time = 5007 Thread tid=3 done Thread[c]: response time = 4945 turnaround time = 7951 execution time = 3006 Thread tid=5 done Thread[d]: response time = 5944 turnaround time = 11953 execution time = 6009 Thread tid=6 done Test2e finished shell[2]% exit exit -->q b e d a c CSS 430: Operating Systems - Process Synchronization

SysLib.join(), Kernel.WAIT public class SysLib { … public static int join( ) { return Kernel.interrupt( Kernel.INTERRUPT_SOFTWARE, Kernel.WAIT, 0, null ); } public class Kernel { public static int interrupt( int irq, int cmd, int param, Object args ) { // Looks like myTcb is not used anywhere; newTcb declared & used below // TCB myTcb; switch( irq ) { case INTERRUPT_SOFTWARE: // System calls switch( cmd ) { case WAIT: // get the current thread id // let the current thread sleep in waitQueue under the // condition = this thread id // System.out.print( " * " ); return OK; // return a child thread id who woke me up CSS 430: Operating Systems - Process Synchronization

enqueueAndSleep(), dequeueAndWakeup() CSS 430: Operating Systems - Process Synchronization

SysLib.exit(), Kernel.EXIT public class SysLib { … public static int exit( ) { return Kernel.interrupt( Kernel.INTERRUPT_SOFTWARE, Kernel.EXIT, 0, null ); } public class Kernel { public static int interrupt( int irq, int cmd, int param, Object args ) { // Looks like myTcb is not used anywhere; newTcb declared & used below // TCB myTcb; switch( irq ) { case INTERRUPT_SOFTWARE: // System calls switch( cmd ) { case EXIT: // get the current thread's parent id // search waitQueue for and wakes up the thread under the // condition = the current thread's parent id // tell the Scheduler to delete the current thread // (since it is exiting) return OK; CSS 430: Operating Systems - Process Synchronization

SysLib.rawread(), Kernel.RAWREAD public class SysLib { … public static int rawread( int blkNumber, byte[] b ) { return Kernel.interrupt( Kernel.INTERRUPT_SOFTWARE, Kernel.RAWREAD, blkNumber, b ); } public class Kernel { public static int interrupt( int irq, int cmd, int param, Object args ) { // Looks like myTcb is not used anywhere; newTcb declared & used below // TCB myTcb; switch( irq ) { case INTERRUPT_SOFTWARE: // System calls switch( cmd ) { case RAWREAD: // read a block of data from disk while ( disk.read( param, ( byte[] )args ) == false ) ioQueue.enqueueAndSleep( COND_DISK_REQ ); while ( disk.testAndResetReady( ) == false ) ioQueue.enqueueAndSleep( COND_DISK_FIN ); return OK; CSS 430: Operating Systems - Process Synchronization

Disk.read(), Disk.testAndResetReady() public class Disk { … public synchronized boolean read( int blockId, byte buffer[] ) { if ( blockId < 0 || blockId > diskSize ) { SysLib.cerr( "threadOS: invalid blockId for read\n" ); return false; } if ( command == IDLE && readyBuffer == false ) { this.buffer = buffer; targetBlockId = blockId; command = READ; notify( ); return true; } else public synchronized boolean testAndResetReady( ) { if ( command == IDLE && readyBuffer == true ) { readyBuffer = false; CSS 430: Operating Systems - Process Synchronization

Disk.waitCommand(), Disk.finishCommand() public class Disk { … private synchronized void waitCommand( ) { while ( command == IDLE ) { try { wait( ); } catch ( InterruptedException e ) { SysLib.cerr( e.toString( ) + "\n" ); } readyBuffer = false; private synchronized void finishCommand( ) { command = IDLE; readyBuffer = true; SysLib.disk( ); // a disk interrupt CSS 430: Operating Systems - Process Synchronization

CSS 430: Operating Systems - Process Synchronization Disk.run() public class Disk { … public void run ( ) { while ( true ) { waitCommand( ); seek( ); switch( command ) { case READ: System.arraycopy( data, targetBlockId * blockSize, buffer, 0, blockSize ); break; case WRITE: case SYNC: } finishCommand( ); CSS 430: Operating Systems - Process Synchronization

Kernel.INTERRUPT_DISK public class SysLib { … public static int rawread( int blkNumber, byte[] b ) { return Kernel.interrupt( Kernel.INTERRUPT_SOFTWARE, Kernel.RAWREAD, blkNumber, b ); } public class Kernel { public static int interrupt( int irq, int cmd, int param, Object args ) { // Looks like myTcb is not used anywhere; newTcb declared & used below // TCB myTcb; switch( irq ) { case INTERRUPT_DISK: // Disk interrupts // wake up the thread waiting for a service completion first ioQueue.dequeueAndWakeup( COND_DISK_FIN ); // wake up a thread waiting for a request acceptance ioQueue.dequeueAndWakeup( COND_DISK_REQ ); return OK; CSS 430: Operating Systems - Process Synchronization