19: Synchronization and More Multithreading Patterns in C#

Create Quick Response Code in C# 19: Synchronization and More Multithreading Patterns
19: Synchronization and More Multithreading Patterns
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a deadlock Instead of locking on this or even typeof(type), it is better to define a private, read-only field on which no one will block except for the class that has access to it Another lock type to avoid is string due to string interning If the same string constant appears within multiple locations it is likely that all locations will refer to the same instance, making the scope of the lock a lot greater than expected In summary, use a per-synchronization context instance of type object for the lock target
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ADVANCED TOPIC Avoid Synchronizing with MethodImplAttribute One synchronization mechanism that was introduced in NET 10 was the MethodImplAttribute Used in conjunction with the MethodImplOptionsSynchronized method, this attribute marks a method as synchronized so that only one thread can execute the method at a time To achieve this, the just-in-time compiler essentially treats the method as though it was surrounded by lock(this) or locking on the type in the case of a static method Such an implementation means that, in fact, the method and all other methods on the same class, decorated with the same attribute and enum parameter, are synchronized, not just each method relative to itself In other words, given two or more methods on the same class decorated with the attribute, only one of them will be able to execute at a time and the one executing will block all calls by other threads to itself or to any other method in the class with the same decoration Furthermore, since the synchronization is on this (or even worse, on the type), it suffers the same detriments as lock(this) (or worse, for the static) discussed in the previous section As a result, it is a best practice to avoid the attribute altogether Declaring Fields as volatile On occasion, the compiler and/or CPU may optimize code in such a way that the instructions do not occur in the exact order they are coded, or some instructions are optimized out Such optimizations are innocuous when code executes on one thread However, with multiple threads, such optimizations may have unintended consequences because the optimizations may
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Synchronization
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change the order of execution of a field s read or write operations relative to an alternate thread s access to the same field One way to stabilize this is to declare fields using the volatile keyword This keyword forces all reads and writes to the volatile field to occur at the exact location the code identifies instead of at some other location that the optimization produces The volatile modifier identifies that the field is susceptible to modification by the hardware, operating system, or another thread As such, the data is volatile, and the keyword instructs the compilers and runtime to handle it more exactly
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Using the SystemThreadingInterlocked Class The mutual exclusion pattern described so far provides the minimum of tools for handling synchronization within a process (application domain) However, synchronization with SystemThreadingMonitor is a relatively expensive operation, and an alternative solution that the processor supports directly targets specific synchronization patterns Listing 195 sets _Data to a new value as long as the preceding value was null As indicated by the method name, this pattern is the compare/ exchange pattern Instead of manually placing a lock around behaviorally equivalent compare and exchange code, the InterlockedCompareExchange() method provides a built-in method for a synchronous operation that does the same check for a value (null) and swaps the first two parameters if the value is equal Table 192 shows other synchronization methods supported by Interlocked
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Listing 195: Synchronization Using SystemThreadingInterlocked
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class SynchronizationUsingInterlocked { private static object _Data; // Initialize data if not yet assigned static void Initialize(object newValue) { // If _Data is null then set it to newValue InterlockedCompareExchange( ref _Data, newValue, null); } // }
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