support for dlopen within threads #1202
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…Task 3) When one thread calls dlopen(), all other running threads in the same cage now automatically get the library instantiated into their Wasm stores via a fire-and-forget epoch interrupt (EPOCH_DLOPEN = 0xd10ad). Runtime changes: - cage/signal: add epoch_dlopen_trigger_others() — sets EPOCH_DLOPEN on all other threads and sends SIGUSR2 to interrupt blocked syscalls - lind-multi-process/signal: add handle_dlopen_replay() — called from signal_handler for all non-main threads; pre-grows the table, calls module_with_child, and registers library symbols for dlsym - lind-boot/execute: drop got_guard before epoch_dlopen_trigger_others to avoid lock contention; call epoch_dlopen_trigger_others after append_module - lind-multi-process/lib: snapshot dlopen_modules at the same point as global_snapshots (before asyncify unwind) to eliminate a TOCTOU race in pthread_create_call - wasmtime/linker: skip apply_global_snapshots when snapshots is empty (the dlopen replay path; globals are set by attach_memory_base/attach_table_base) - lind-utils (LindGOT::new_entry): pre-fill duplicate GOT handlers from symbol_cache so replaying threads see correct function table indices Test (thread_dlopen_concurrent.c): Uses a two-barrier design — workers first signal via g_ready that they are registered, then main calls dlopen (EPOCH_DLOPEN fires on all workers), then main releases via g_go. The epoch check at pthread_barrier_wait's Wasm function entry delivers handle_dlopen_replay before any library call. lib.c: add add(int,int) export used by the new test.
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dlopen within threads: epoch-based cross-thread library replay (#1028 Task 3)
When one thread calls
dlopen()while other threads are already running, the newly-loaded library must be instantiated into every running thread's Wasm store. Previously this was unsupported (guarded with a panic).Mechanism (fire-and-forget)
epoch_dlopen_trigger_others()setsEPOCH_DLOPEN(0xd10ad) on all other registered threads and sendsSIGUSR2to interrupt any blocked syscallshandle_dlopen_replay()runs inside each thread's epoch callback: pre-grows the shared function table, instantiates the library viamodule_with_child, and pre-fills GOT cells fromsymbol_cacheso function indices are correct without a full GOT updateLindGOT::new_entrypre-fills duplicate GOT handlers from cache so replaying threads immediately see valid function table indiceshandle_dlopen_replaydlopen_modulesis snapshotted at the same point asglobal_snapshots(before asyncify unwind inpthread_create_call) to eliminate a TOCTOU raceLimitation
The epoch fires at Wasm function entries. Application code must ensure at least one function-call epoch checkpoint is reached between when dlopen fires and when worker threads first call into the newly-loaded library. The test enforces this with a two-barrier design: workers signal they are registered before main calls dlopen, then wait on a second barrier whose function-entry epoch check delivers the replay.
Test
thread_dlopen_concurrent.c— 4 workers block ong_ready(guaranteeing registration), main callsdlopen, then releases viag_go. Workers verify the library via both an inherited function pointer and an independentdlsymcall. Passes 15/15 runs consistently.