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From: Jeff Hostetler <git@jeffhostetler.com>
To: Junio C Hamano <gitster@pobox.com>,
	Jeff Hostetler via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Jeff Hostetler <jeffhost@microsoft.com>
Subject: Re: [PATCH 2/9] trace2: convert tr2tls_thread_ctx.thread_name from strbuf to char*
Date: Wed, 22 Dec 2021 11:28:23 -0500	[thread overview]
Message-ID: <ea4eb7f2-863f-2439-d175-cd4e97ad63a6@jeffhostetler.com> (raw)
In-Reply-To: <xmqqsfumqv62.fsf@gitster.g>



On 12/21/21 2:22 AM, Junio C Hamano wrote:
> "Jeff Hostetler via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> From: Jeff Hostetler <jeffhost@microsoft.com>
>>
>> Use a 'char *' to hold the thread name rather than a 'struct strbuf'.
>> The thread name is set when the thread is created and should not be
>> be modified afterwards.  Replace the strbuf with an allocated pointer
>> to make that more clear.
> 
> Sounds good.  Use of strbuf is perfectly fine while you compute the
> final value of the string, but as a more permanent location to store
> the result, it often is unsuitable (and strbuf_split_buf() is a prime
> example of how *not* to design your API function around the type).
> 
>> diff --git a/trace2/tr2_tls.c b/trace2/tr2_tls.c
>> index 7da94aba522..cd8b9f2f0a0 100644
>> --- a/trace2/tr2_tls.c
>> +++ b/trace2/tr2_tls.c
>> @@ -35,6 +35,7 @@ struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name,
>>   					     uint64_t us_thread_start)
>>   {
>>   	struct tr2tls_thread_ctx *ctx = xcalloc(1, sizeof(*ctx));
>> +	struct strbuf buf_name = STRBUF_INIT;
>>   
>>   	/*
>>   	 * Implicitly "tr2tls_push_self()" to capture the thread's start
>> @@ -47,12 +48,13 @@ struct tr2tls_thread_ctx *tr2tls_create_self(const char *thread_name,
>>   
>>   	ctx->thread_id = tr2tls_locked_increment(&tr2_next_thread_id);
>>   
>> -	strbuf_init(&ctx->thread_name, 0);
>>   	if (ctx->thread_id)
>> -		strbuf_addf(&ctx->thread_name, "th%02d:", ctx->thread_id);
>> -	strbuf_addstr(&ctx->thread_name, thread_name);
>> -	if (ctx->thread_name.len > TR2_MAX_THREAD_NAME)
>> -		strbuf_setlen(&ctx->thread_name, TR2_MAX_THREAD_NAME);
>> +		strbuf_addf(&buf_name, "th%02d:", ctx->thread_id);
>> +	strbuf_addstr(&buf_name, thread_name);
>> +	if (buf_name.len > TR2_MAX_THREAD_NAME)
>> +		strbuf_setlen(&buf_name, TR2_MAX_THREAD_NAME);
>> +
>> +	ctx->thread_name = strbuf_detach(&buf_name, NULL);
> 
> This is not exactly a new problem, but if we use a mechanism to
> allow arbitrary long string (like composing with strbuf and
> detaching the resulting string as is), instead of having a fixed
> name[] array embedded in the ctx structure, I wonder if applying the
> maximum length this early makes sense.  Such a truncation would
> allow more than one ctx structures to share the same name, which
> somehow feels error prone, inviting a mistake to use .thread_name
> member as an identifier, when its only intended use is to give a
> human-readable and not necessarily unique label.  Of course, if the
> maximum is reasonably low, like a few dozen bytes, it may even make
> sense to embed an array of the fixed size and not worry about an
> extra pointer.
> 

I'll convert it to a flex-array at the bottom of the CTX structure
and then defer the truncation to the _perf target (which only does
that to keep the columns lined up).

That will simplify things considerably.

Thanks
Jeff


  reply	other threads:[~2021-12-22 16:28 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-20 15:01 [PATCH 0/9] Trace2 stopwatch timers and global counters Jeff Hostetler via GitGitGadget
2021-12-20 15:01 ` [PATCH 1/9] trace2: use size_t alloc,nr_open_regions in tr2tls_thread_ctx Jeff Hostetler via GitGitGadget
2021-12-20 15:01 ` [PATCH 2/9] trace2: convert tr2tls_thread_ctx.thread_name from strbuf to char* Jeff Hostetler via GitGitGadget
2021-12-20 16:31   ` Ævar Arnfjörð Bjarmason
2021-12-20 19:07     ` Jeff Hostetler
2021-12-20 19:35       ` Ævar Arnfjörð Bjarmason
2021-12-22 16:32         ` Jeff Hostetler
2021-12-21  7:33     ` Junio C Hamano
2021-12-21  7:22   ` Junio C Hamano
2021-12-22 16:28     ` Jeff Hostetler [this message]
2021-12-22 19:57       ` Junio C Hamano
2021-12-20 15:01 ` [PATCH 3/9] trace2: defer free of TLS CTX until program exit Jeff Hostetler via GitGitGadget
2021-12-21  7:30   ` Junio C Hamano
2021-12-22 21:59     ` Jeff Hostetler
2021-12-22 22:56       ` Junio C Hamano
2021-12-22 23:04         ` Jeff Hostetler
2021-12-23  7:38         ` Johannes Sixt
2021-12-23 18:18           ` Junio C Hamano
2021-12-27 18:51             ` Jeff Hostetler
2021-12-20 15:01 ` [PATCH 4/9] trace2: add thread-name override to event target Jeff Hostetler via GitGitGadget
2021-12-20 15:01 ` [PATCH 5/9] trace2: add thread-name override to perf target Jeff Hostetler via GitGitGadget
2021-12-20 15:01 ` [PATCH 6/9] trace2: add timer events to perf and event target formats Jeff Hostetler via GitGitGadget
2021-12-20 16:39   ` Ævar Arnfjörð Bjarmason
2021-12-20 19:44     ` Jeff Hostetler
2021-12-21 14:20   ` Derrick Stolee
2021-12-20 15:01 ` [PATCH 7/9] trace2: add stopwatch timers Jeff Hostetler via GitGitGadget
2021-12-20 16:42   ` Ævar Arnfjörð Bjarmason
2021-12-22 21:38     ` Jeff Hostetler
2021-12-21 14:45   ` Derrick Stolee
2021-12-22 21:57     ` Jeff Hostetler
2021-12-20 15:01 ` [PATCH 8/9] trace2: add counter events to perf and event target formats Jeff Hostetler via GitGitGadget
2021-12-20 16:51   ` Ævar Arnfjörð Bjarmason
2021-12-22 22:56     ` Jeff Hostetler
2021-12-20 15:01 ` [PATCH 9/9] trace2: add global counters Jeff Hostetler via GitGitGadget
2021-12-20 17:14   ` Ævar Arnfjörð Bjarmason
2021-12-22 22:18     ` Jeff Hostetler
2021-12-21 14:51 ` [PATCH 0/9] Trace2 stopwatch timers and " Derrick Stolee
2021-12-21 23:27   ` Matheus Tavares
2021-12-28 19:36 ` [PATCH v2 " Jeff Hostetler via GitGitGadget
2021-12-28 19:36   ` [PATCH v2 1/9] trace2: use size_t alloc,nr_open_regions in tr2tls_thread_ctx Jeff Hostetler via GitGitGadget
2021-12-29  0:48     ` Ævar Arnfjörð Bjarmason
2021-12-28 19:36   ` [PATCH v2 2/9] trace2: convert tr2tls_thread_ctx.thread_name from strbuf to flex array Jeff Hostetler via GitGitGadget
2021-12-29  1:11     ` Ævar Arnfjörð Bjarmason
2021-12-29 16:46       ` Jeff Hostetler
2021-12-28 19:36   ` [PATCH v2 3/9] trace2: defer free of thread local storage until program exit Jeff Hostetler via GitGitGadget
2021-12-28 19:36   ` [PATCH v2 4/9] trace2: add thread-name override to event target Jeff Hostetler via GitGitGadget
2021-12-28 19:36   ` [PATCH v2 5/9] trace2: add thread-name override to perf target Jeff Hostetler via GitGitGadget
2021-12-29  1:48     ` Ævar Arnfjörð Bjarmason
2021-12-29 17:15       ` Jeff Hostetler
2021-12-28 19:36   ` [PATCH v2 6/9] trace2: add timer events to perf and event target formats Jeff Hostetler via GitGitGadget
2021-12-28 19:36   ` [PATCH v2 7/9] trace2: add stopwatch timers Jeff Hostetler via GitGitGadget
2021-12-28 19:36   ` [PATCH v2 8/9] trace2: add counter events to perf and event target formats Jeff Hostetler via GitGitGadget
2021-12-28 19:36   ` [PATCH v2 9/9] trace2: add global counters Jeff Hostetler via GitGitGadget
2021-12-29  1:54   ` [PATCH v2 0/9] Trace2 stopwatch timers and " Ævar Arnfjörð Bjarmason
2021-12-30 16:42     ` Jeff Hostetler

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