Data race on `ctx->threadLimit` between `POOL_thread()` and `POOL_create_advanced()`

[guoyuqi020]

It seems that the ctx->threadLimit variable is updated in POOL_create_advanced() without being protected by the ctx->queueMutex. This can lead to a data race. Will this be a problem?

zstd/lib/common/pool.c

Lines 67 to 90 in bfd8ad8

	static void* POOL_thread(void* opaque) {
	POOL_ctx* const ctx = (POOL_ctx*)opaque;
	if (!ctx) { return NULL; }
	for (;;) {
	/* Lock the mutex and wait for a non-empty queue or until shutdown */
	ZSTD_pthread_mutex_lock(&ctx->queueMutex);
	while ( ctx->queueEmpty
	|| (ctx->numThreadsBusy >= ctx->threadLimit) ) {
	if (ctx->shutdown) {
	/* even if !queueEmpty, (possible if numThreadsBusy >= threadLimit),
	* a few threads will be shutdown while !queueEmpty,
	* but enough threads will remain active to finish the queue */
	ZSTD_pthread_mutex_unlock(&ctx->queueMutex);
	return opaque;
	}
	ZSTD_pthread_cond_wait(&ctx->queuePopCond, &ctx->queueMutex);
	}
	/* Pop a job off the queue */
	{ POOL_job const job = ctx->queue[ctx->queueHead];
	ctx->queueHead = (ctx->queueHead + 1) % ctx->queueSize;
	ctx->numThreadsBusy++;
	ctx->queueEmpty = (ctx->queueHead == ctx->queueTail);
	/* Unlock the mutex, signal a pusher, and run the job */

zstd/lib/common/pool.c

Lines 143 to 159 in bfd8ad8

	ctx->threads = (ZSTD_pthread_t*)ZSTD_customCalloc(numThreads * sizeof(ZSTD_pthread_t), customMem);
	ctx->threadCapacity = 0;
	ctx->customMem = customMem;
	/* Check for errors */
	if (!ctx->threads || !ctx->queue) { POOL_free(ctx); return NULL; }
	/* Initialize the threads */
	{ size_t i;
	for (i = 0; i < numThreads; ++i) {
	if (ZSTD_pthread_create(&ctx->threads[i], NULL, &POOL_thread, ctx)) {
	ctx->threadCapacity = i;
	POOL_free(ctx);
	return NULL;
	} }
	ctx->threadCapacity = numThreads;
	ctx->threadLimit = numThreads;
	}
	return ctx;