Questions and Answers
What does priority ceiling aim to achieve?
Priority inheritance allows a low priority thread to run freely when holding a mutex.
False
Name a mechanism that Windows uses to prevent priority inversions.
Random boosting
Threads within the same process share a _________.
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What is the main goal of inter-process communication?
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Match the synchronization mechanisms with their descriptions:
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Threads getting in each other’s way is a desired behavior in concurrency.
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What is one key question to address when supporting concurrency?
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Which of the following is NOT a communication mechanism between processes?
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Message passing allows processes to share memory directly.
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Name one primitive used in message passing.
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In message passing, the function 'send' is used to send a message to a specified ______.
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Match the communication mechanisms with their descriptions:
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What happens when a caller attempts to receive a message that is not available?
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In UNIX systems, file descriptors are used for message passing through sockets.
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What type of communication might 'source' in message passing refer to?
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Message passing can be used for both ______ and over-the-network communication.
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What is a common use case for message passing?
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What is the purpose of a sequence identifier in message passing?
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Message passing interfaces incur performance costs due to multiple copies.
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What function is used to create a socket in UNIX?
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In message passing, we need to avoid communicating with an ________ participant.
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Match the inter-process communication mechanism with its description:
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What is the main purpose of a signal in inter-process communication?
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Signals are always synchronous and occur in response to specific events.
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Which of the following is a cost associated with system calls in message passing?
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What function is typically used to send signals to a process?
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Sockets provide an interface specifically designed for file communication, not network communications.
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In inter-process communication, mutual exclusion ensures that shared resources are accessed by only one __________ at a time.
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What are the two points where messages are typically copied in message passing?
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Match the signal number with its corresponding reason:
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The process of ensuring we are communicating with the correct process is known as ________.
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What is one crucial feature provided by the OS in message passing?
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What happens in the no buffering scheme of message passing?
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Message passing can only implement communication locally.
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What is the purpose of sending an acknowledgement message in message passing?
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In message passing, data can be ___ between address spaces when messages are sent.
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Match the following message passing schemes with their characteristics:
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What is a limitation of message passing over networks?
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Message passing embeds synchronization semantics.
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What happens when the buffer is full in the buffering scheme of message passing?
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The function used by the producer to generate data is called ___ .
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Which of the following functions does the consumer use to process received messages?
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Study Notes
Scheduling and Priority Mechanisms
- Priority Inversion: The rationale behind scheduling algorithms can fail if a high-priority thread is unable to run due to a lower-priority thread holding a resource.
- Priority Ceiling Protocol: Assigns a high priority to mutexes, ensuring that any thread holding it has priority above threads needing the mutex, thus preventing priority inversions.
- Priority Inheritance Protocol: Temporarily boosts the priority of a low-priority thread that holds a mutex needed by a higher-priority thread, allowing swift mutex release while maintaining system priorities.
- Random Boosting: Mechanism that randomly increases the priority of mutex holders to expedite critical section completion; used by Windows operating systems to mitigate priority inversions.
Supporting Concurrency
- Three essential considerations for concurrency support:
- Processes must communicate effectively.
- Ensuring threads operate without interference.
- Synchronizing thread behavior.
Inter-Process Communication (IPC)
- Shared Address Space: Threads within the same process can share memory, simplifying information exchange.
- Message Acknowledgment: Messages typically include sequence identifiers to manage received messages and detect duplicates.
- Authentication: Ensures proper identification of processes during communication to prevent interactions with unauthorized entities.
- Performance Costs: Message passing can incur overhead from multiple copies of messages and context switching between user and kernel modes.
Sockets
- Sockets are special files in UNIX that bind to network interfaces, providing a tailored API for message passing and network communication.
- They enable data exchange via buffers and variables, aiding communication between isolated processes.
Message Passing
-
Basics: Operates on send and receive primitives implemented as system calls.
-
send(destination, &message)
: Sends a message to a specified destination. -
receive(source, &message)
: Receives a message from a specified source.
-
- Communication can occur between local processes or over a network through sockets.
- Synchronizing Semantics: Message passing inherently incorporates synchronization due to its communication nature.
Message Passing: Buffers
- No Buffering: The sender blocks until the message is received with no intermediate storage.
- Buffered Communication: The kernel maintains a limited queue of messages, allowing senders to transmit without blocking until the buffer is full.
Message Passing: Limitations
- Data Loss: When communicating over networks, messages may get lost; acknowledgments can help confirm receipt and trigger retransmission if necessary.
- Security Risks: Increased vulnerabilities when handling messages over networks, necessitating robust communication protocols.
Signals
- Signal Mechanism: Asynchronous notifications sent between processes that invoke a signal handler based on signal numbers (e.g., KILL, STOP).
-
Sending Signals: Executed through the
kill(pid_t pid, int sig_nr)
function. -
Signal Handling: Processes manage signals via defined signal handlers, which can be modified using functions like
signal()
orsigaction()
. - Synchronicity: Signals operate asynchronously; they can be triggered at any time, usually upon interrupts or system calls.
- Signal Count: Processes cannot track the number of signals received before handling, as they are represented only in a bitmask.
Deadlocks
- Mutual Exclusion: Access to shared resources must be controlled, permitting only one thread at a time to avoid deadlocks.
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Description
This quiz covers key concepts in scheduling algorithms, focusing on priority ceiling and priority inheritance mechanisms. Understand how these methods help prevent priority inversions and manage thread priorities effectively. Test your knowledge on the implications of mutexes in real-time systems.