Fix Thread::start() and general_block_device test's thread allocation/deallocation #15059
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When a Thread object's stack memory is not provided, its `start()` member function dynamically allocates its stack from the heap. If allocation fails, there is no way to catch it because * `std::nothrow` is missing after the `new` keyword. As Mbed OS is built with `-fno-exceptions` (C++ exceptions disabled), failed allocation results in an unrecoverable fault. * The attempted `nullptr` check, which doesn't work anyway due to the first point, is an assertion instead of error returning. Assertions should be used as a development tool to ensure code behaves correctly. But out-of-memory is a completely valid runtime situation. This commit adds the missing `std::nothrow`, and makes `Thread::start()` return `osErrorNoMemory` if allocation fails so the caller can handle it. Note: A case when a thread should never fail due to lack of memory is the main thread. But the main thread's stack is a pre-allocated array in the static memory, passed to the `Thread()` constructor during thread creation, so it's not impacted by this change.
The test case for multithreaded erase/program/read allocates a few Thread objects from the heap and starts them. It has a few problems: * To check that there will be enough heap to start a new thread, the test case tries to allocate a dummy buffer of the thread's heap size and then frees it, before starting the thread. Then the thread will allocate its own stack. Such check is not reliable, because threads that are already running also perform additional allocation (when running `test_thread_job()`) and may take away the memory we just checked. * When deleting all threads in a loop, the loop boundary misses the last thread if the last thread object was allocated but not started (i.e. due to failed thread stack allocation check). To fix the issues * Start a thread without any allocation test. Following the preceding commit "rtos: Thread: Make stack allocation failure runtime catchable", `Thread::start()` now returns `osErrorNoMemory` if stack allocation fails which we can handle. * Store pointers to all threads in a zero-initialized array, and free all elements at the end of the test.
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Summary of changes
This issues were identified while working on QSPI flash support for CYW9P62S1_43012EVB_01 (#14989).
rtos::Threadclass: If a thread's stack memory is not preallocated,Thread::start()allocates its stack from the heap. Allocation is asserted to succeed and not runtime-catchable, and this assertion doesn't even work due to missingstd::nothrow. The system crashes in this case.test_thread_job()) and may take away the memory we just checked.To fix the issues above
rtos::Thread: Add missingstd::nothrowto stack allocation. If allocation returnsnullptr, makestart()returnosErrorNoMemoryosErrorNoMemoryreturn value fromThread::start().Impact of changes
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