Bit-fields allow for a simple way to break portions of a struct into portions that only use up a certain may be used to declare struct members that use only a specified number of bits. If multiple threads are accessing or making modifications to different bit-fields, a race condition may be present because the architecture may not be able to modify only the bits to which the currently being modified member may refer. ThereforeAs a result, a mutex protecting all bit-fields at the same time must be used.
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In the following non-compliant code, two executing threads presumed to be running simultaneously access two separate members of a global struct.
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Although this appears to be harmless, it is possible (and likely) that the architecture that this is running on has aligned flag1 and flag2 on are stored in the same byte. If both assignments occur on a thread scheduling interleaving which ends with the both stores occurring after one another, it is possible that only one of the flags will be set as intended and the other flag will equal its previous value due to the fact that both of the . This is because both bit-fields fell on are represented by the same byte, which was is the smallest unit the processor could work on.
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Even though each thread is modifying a separate bit-field, they are both modifying the same location in memory. This is the same problem discussed in POS00-A. Avoid race conditions with multiple threads, but worse is harder to diagnose because it is not obvious at first glance that the same memory location is being modified.
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