Java SyncFailedException Class
Last modified: April 16, 2025
The java.io.SyncFailedException signals that a sync operation has
failed. This occurs when the system cannot guarantee that buffers have been
written to physical storage. It extends IOException and is thrown
by FileDescriptor.sync and RandomAccessFile.getFD().sync.
Sync operations ensure file contents are physically written to storage. When this fails, data might be lost if the system crashes. This exception indicates a serious I/O problem that should be handled appropriately.
SyncFailedException Class Overview
SyncFailedException is a checked exception in Java's I/O system.
It has a simple constructor that takes a descriptive message. The exception
provides standard methods inherited from IOException.
public class SyncFailedException extends IOException {
public SyncFailedException(String desc);
}
The code above shows the complete class definition. The constructor creates an exception with a description of the failure. This helps diagnose why the sync operation couldn't complete successfully.
Basic SyncFailedException Example
This example demonstrates how a SyncFailedException might occur
when trying to sync a file descriptor. We attempt to force system buffers to
disk but handle potential failures.
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.SyncFailedException;
public class Main {
public static void main(String[] args) {
try (FileOutputStream fos = new FileOutputStream("data.txt")) {
fos.write("Important data".getBytes());
// Attempt to sync file contents to disk
fos.getFD().sync();
System.out.println("Data successfully synced to disk");
} catch (SyncFailedException e) {
System.err.println("Failed to sync data: " + e.getMessage());
} catch (IOException e) {
System.err.println("I/O error: " + e.getMessage());
}
}
}
This example shows basic sync operation handling. The getFD().sync
call forces data to disk. If this fails, we catch SyncFailedException
separately from other I/O errors. This allows specific handling of sync failures.
Handling Sync Failure in RandomAccessFile
RandomAccessFile also supports sync operations through its file
descriptor. This example shows sync failure handling with random file access.
We write data and attempt to force it to disk.
import java.io.IOException;
import java.io.RandomAccessFile;
import java.io.SyncFailedException;
public class Main {
public static void main(String[] args) {
try (RandomAccessFile raf = new RandomAccessFile("random.dat", "rw")) {
raf.write("Critical information".getBytes());
// Force changes to disk
raf.getFD().sync();
System.out.println("Random access file synced successfully");
} catch (SyncFailedException e) {
System.err.println("Sync failed! Data may be at risk: " + e.getMessage());
// Implement recovery strategy here
} catch (IOException e) {
System.err.println("General I/O error: " + e.getMessage());
}
}
}
This example demonstrates sync operation with RandomAccessFile.
The sync failure is caught separately for special handling. In real applications,
you might implement data recovery or notification when sync fails.
Checking FileDescriptor Validity Before Sync
Before attempting sync, it's good practice to check if the file descriptor is valid. This example shows how to validate the descriptor and handle sync failure.
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.SyncFailedException;
public class Main {
public static void main(String[] args) {
try (FileOutputStream fos = new FileOutputStream("check.txt")) {
fos.write("Test data".getBytes());
if (fos.getFD().valid()) {
try {
fos.getFD().sync();
System.out.println("Sync completed successfully");
} catch (SyncFailedException e) {
System.err.println("Sync failed despite valid FD: " + e.getMessage());
}
} else {
System.err.println("File descriptor is invalid - cannot sync");
}
} catch (IOException e) {
System.err.println("I/O error: " + e.getMessage());
}
}
}
This example checks file descriptor validity before attempting sync. Even with a valid descriptor, sync can fail due to system-level issues. The example shows proper error handling for both cases.
Retry Mechanism for Sync Operations
When sync fails, you might want to retry the operation. This example implements a simple retry mechanism with exponential backoff for sync operations.
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.SyncFailedException;
public class Main {
private static final int MAX_RETRIES = 3;
private static final long INITIAL_DELAY = 100; // milliseconds
public static void main(String[] args) {
try (FileOutputStream fos = new FileOutputStream("retry.txt")) {
fos.write("Important transaction".getBytes());
boolean synced = false;
long delay = INITIAL_DELAY;
for (int i = 0; i < MAX_RETRIES && !synced; i++) {
try {
fos.getFD().sync();
synced = true;
System.out.println("Sync succeeded on attempt " + (i + 1));
} catch (SyncFailedException e) {
System.err.println("Sync attempt " + (i + 1) + " failed");
if (i < MAX_RETRIES - 1) {
try {
Thread.sleep(delay);
delay *= 2; // Exponential backoff
} catch (InterruptedException ie) {
Thread.currentThread().interrupt();
break;
}
}
}
}
if (!synced) {
System.err.println("Failed to sync after " + MAX_RETRIES + " attempts");
// Implement fallback strategy here
}
} catch (IOException e) {
System.err.println("I/O error: " + e.getMessage());
}
}
}
This example shows a robust sync operation with retries. Each failed attempt increases the delay between retries. After maximum retries, it reports failure. In production, you might log this event or implement data recovery procedures.
Differentiating Sync Failures from Other IOExceptions
It's important to distinguish sync failures from other I/O errors. This example shows how to handle different exception types appropriately.
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.SyncFailedException;
public class Main {
public static void main(String[] args) {
try (FileOutputStream fos = new FileOutputStream("data.bin")) {
// Write important binary data
byte[] data = new byte[1024];
// ... fill data array ...
fos.write(data);
try {
fos.getFD().sync();
} catch (SyncFailedException e) {
// Specific handling for sync failures
System.err.println("WARNING: Sync failed - " + e.getMessage());
System.err.println("Data might not be persisted to disk");
// Additional handling specific to sync failure
}
} catch (IOException e) {
// General I/O error handling
System.err.println("ERROR: I/O operation failed - " + e.getMessage());
// Different handling for non-sync related errors
}
}
}
This example demonstrates separate handling for sync failures versus other I/O errors. Sync failures get specific warnings about potential data persistence issues. Other I/O errors are handled more generally.
Logging Sync Failures for Diagnostics
Proper logging of sync failures helps diagnose system issues. This example shows how to log sync failures with detailed information.
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.SyncFailedException;
import java.time.Instant;
import java.util.logging.Level;
import java.util.logging.Logger;
public class Main {
private static final Logger logger = Logger.getLogger(Main.class.getName());
public static void main(String[] args) {
String filename = "transaction.log";
try (FileOutputStream fos = new FileOutputStream(filename)) {
String transaction = "TX1001,500.00,ACCT123";
fos.write(transaction.getBytes());
try {
fos.getFD().sync();
logger.info("Transaction committed and synced to disk");
} catch (SyncFailedException e) {
logger.log(Level.SEVERE, "Failed to sync transaction file", e);
logger.severe("Transaction may not be persisted: " + filename);
logger.severe("Failure timestamp: " + Instant.now());
// Additional recovery logic here
}
} catch (IOException e) {
logger.log(Level.SEVERE, "Failed to write transaction", e);
}
}
}
This example uses Java's logging framework to record sync failures. It captures the exact time of failure and file details. Such logging helps administrators diagnose and address storage system problems.
Source
Java SyncFailedException Class Documentation
In this article, we've covered the Java SyncFailedException class
with practical examples. Understanding sync operations and their failure modes
is crucial for building robust, data-safe applications.
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