Bug 1810244 - restrict use of dynamic thread names via moz_task r=application-update-reviewers,bytesized,emilio

Bug 1613440 added a checker to prevent a profusion of new threads.
Unfortunately, it operates directly on C++ source code, and there is no
equivalent for Rust code.

It _is_ possible to construct such an equivalent (see bug 1810242), but
it's nontrivial. For now, let's just prevent the use of dynamic thread
names, to minimize the profusion of uninterestingly-distinct thread
names in our `XPCOMSpinEventLoopStack` crash-report field.

Differential Revision: https://phabricator.services.mozilla.com/D166842

toolkit/components/bitsdownload/src/bits_interface/request.rs

@@ -139,7 +139,7 @@ impl BitsRequest {
     ) -> Result<RefPtr<BitsRequest>, BitsTaskError> {
         let _ = context;
         let action: Action = action.into();
-        let monitor_thread = create_thread(&format!("BitsMonitor {}", id)).map_err(|rv| {
+        let monitor_thread = create_thread("BitsMonitor").map_err(|rv| {
             BitsTaskError::from_nsresult(FailedToStartThread, action, MainThread, rv)
         })?;
 

xpcom/rust/moz_task/src/lib.rs

@@ -66,7 +66,10 @@ pub fn is_main_thread() -> bool {
     unsafe { NS_IsMainThread() }
 }
 
-pub fn create_thread(name: &str) -> Result<RefPtr<nsIThread>, nsresult> {
+// There's no OS requirement that thread names be static, but dynamic thread
+// names tend to conceal more than they reveal when processing large numbers of
+// crash reports.
+pub fn create_thread(name: &'static str) -> Result<RefPtr<nsIThread>, nsresult> {
     getter_addrefs(|p| unsafe {
         NS_NewNamedThreadWithDefaultStackSize(&*nsCString::from(name), p, ptr::null())
     })